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METHODOLOGIES FOR ECOLOGICAL MONITORING IN BIOENERGY CROPS A review and recommendations ADAS Contract Report for the Department for Environment, Food and Rural Affairs Defra Project NF0408 Chris Britt August 2003 (Revised December 2003) CONTENTS CONTENTS .................................................................................................................................... 1 EXECUTIVE SUMMARY ................................................................................................................ 2 Objectives and scope ...................................................................................................................... 2 Biomass crop production ................................................................................................................. 2 Environmental impacts of biomass crops ....................................................................................... 2 Objectives of ecological surveys and monitoring ............................................................................ 2 1. 1.1 1.2 1.3 1.4 INTRODUCTION ................................................................................................................. 8 Objectives and scope .......................................................................................................... 8 Biomass crop production ..................................................................................................... 8 Environmental impacts of biomass crops ............................................................................ 9 Objectives of ecological surveys and monitoring .............................................................. 11 2. 2.1 2.2 ECOLOGICAL MONITORING .......................................................................................... 13 Practical considerations ..................................................................................................... 13 Ecological monitoring programmes and networks ............................................................. 13 3. 3.1 3.2 3.3 3.4 PLANTS............................................................................................................................. 15 Botanical species diversity in biomass crops .................................................................... 15 Standard botanical survey methods .................................................................................. 16 Botanical survey methods applied in studies of biomass crops ........................................ 19 Advantages and disadvantages of different methods in relation to surveys in biomass crops .................................................................................................................................. 21 4. 4.1 4.2 4.3 4.4 INVERTEBRATES ............................................................................................................ 23 Invertebrate species diversity in biomass crops ................................................................ 23 Standard invertebrate survey methods .............................................................................. 24 Invertebrate survey methods applied in studies of biomass crops .................................... 33 Advantages and disadvantages of different methods in relation to surveys in biomass crops .................................................................................................................................. 34 5. 5.1 5.2 5.3 5.4 BIRDS ................................................................................................................................ 36 Bird species diversity in biomass crops ............................................................................. 36 Standard bird survey methods ........................................................................................... 38 Bird survey methods applied in studies of biomass crops ................................................. 41 Advantages and disadvantages of different methods in relation to surveys in biomass crops .................................................................................................................................. 41 6. 6.1 6.2 6.3 6.4 MAMMALS ........................................................................................................................ 43 Mammal species diversity in biomass crops ..................................................................... 43 Standard mammal survey methods ................................................................................... 44 Mammal survey methods applied in studies of biomass crops ......................................... 47 Advantages and disadvantages of different methods in relation to surveys in biomass crops .................................................................................................................................. 48 7. 7.1 7.2 7.3 7.4 REPTILES AND AMPHIBIANS ........................................................................................ 50 Reptile and amphibian species diversity in biomass crops ............................................... 50 Standard reptile and amphibian survey methods .............................................................. 50 Reptile and amphibian survey methods applied in studies of biomass crops ................... 51 Advantages and disadvantages of different methods in relation to surveys in biomass crops .................................................................................................................................. 52 8. RECOMMENDATIONS ..................................................................................................... 53 9. ACKNOWLEDGEMENTS ................................................................................................. 55 10. REFERENCES .................................................................................................................. 56 1 EXECUTIVE SUMMARY Objectives and scope 1. The main objectives of the work described in this report were to review methodologies used for ecological monitoring in short rotation poplar and willow, and other biomass (bioenergy) crops, and to recommend standardised methods for future projects. 2. This report considers currently available information on the biodiversity of bioenergy crops and reviews the methods employed in previous research, survey and monitoring projects. It also summarises standard ecological monitoring methodologies for plants, invertebrates, birds, mammals, reptiles and amphibians – and evaluates the practical advantages and disadvantages of different techniques for studies of species diversity in bioenergy crops. 3. The report recommends that new projects for the ecological monitoring of bioenergy crops in the UK should be encouraged to adopt a standard suite of protocols, although this should not preclude originality or the inclusion of additional species or groups. 4. The report does not prescribe suitable protocols, but sets out 11 basic principles to be considered (see paragraph 48 below) and provides clear guidance on the likely suitability, or otherwise, of many commonly used ecological monitoring methods. Biomass crop production 5. Bioenergy crops, which include short rotation coppice (SRC) and energy grasses, are likely to make a major contribution to Government targets for increased use of renewable energy sources and reduced carbon dioxide emissions. 6. The main bioenergy crops likely to be grown in the UK are willow and poplars SRC, Miscanthus grass and whole crop cereals. Other potential candidates, for the longer-term, include other grass species such as reed canary grass (Phalaris arundinacea), switchgrass (Panicum virgatum) and giant reed (Arundo donax). Environmental impacts of biomass crops 7. Bioenergy crops provide several potential environmental benefits, including greenhouse gas reduction, reduced nutrient leaching, reduced soil erosion and phytoremediation of contaminated soils. 8. One very important consideration, before widespread planting of any new crop is actively encouraged, is the probable impacts on biodiversity. This aspect is only partially (in the case of SRC) or poorly (in the case of energy grasses) understood. However, in most cases, biodiversity is likely to be low in comparison with most semi-natural habitats – but will vary considerably, depending on factors such as management practices, plantation size and location. 9. Impacts on biodiversity should be considered on a landscape scale and viewed in the context of the crop or other land-use that it is replacing. Objectives of ecological surveys and monitoring 10. The objectives of any ecological survey or monitoring must be considered at the outset, as these will have an important influence on methodologies used. Objectives might include: describing the interest of sites, estimating population size, 2 monitoring population changes, determining the habitat requirements of a species, determining why species have declined, monitoring habitat management and studying population dynamics. Ecological monitoring 11. The methodologies used for ecological monitoring will be determined primarily by the scientific objectives, available resources and practical considerations. 12. Bioenergy crops are usually very densely planted and may be difficult to walk through, particularly when carrying bulky equipment. Their height and density will also restrict visibility through the crop for much of the year. Crop plants may impede the placement of quadrats. Relocation of ‘permanent’ quadrats or recording points may be difficult. 13. Previous ecological monitoring of bioenergy crops in the UK, almost exclusively in SRC, has focused primarily on plants, arboreal invertebrates and birds. More work is needed to broaden our understanding of the ecological function of SRC crops within the broader landscape. Studies on the ecology of Miscanthus and other energy grasses are urgently needed. Plants 14. The ground flora of SRC plantations on ex-agricultural sites tends to be dominated by a small number of competitive or ruderal weed species. In dense, well managed plantations, ground cover is sparse and shade-tolerant species relatively important. In less dense, poorly managed plantations (with inadequate weed control), percentage ground cover can be much higher and open-ground species predominant. Other factors affecting botanical composition include plantation age, previous land use and the proximity of woodland. 15. Species lists can be compiled for any site, or part of a site, but more useful data will be obtained from assessments of cover, biomass or frequency. Another alternative is vegetation mapping. Careful thought must be given to the choice of survey period and the possible need for surveys in more than one period each year. 16. Previous botanical surveys in SRC have used linear quadrats (e.g. 4 x 1 m or 10 x 1 m) and simple estimates of cover (e.g. DAFOR scale) and frequency. Plant frequency measurements using ‘nested’ quadrats were used in one study of UK poplar plantations. Classification of species present using primary ecological strategies, or plant communities using the National Vegetation Classification (NVC) system, have been used to aid analysis and interpretation of ground vegetation data. 17. Botanical monitoring in bioenergy crops should consider the practical difficulties of placing quadrats across crop rows, but also take account of the fact that surveys confined to inter-row areas may provide data that are not representative of plant species diversity across the whole site. For example, in SRC, different physical conditions within rows may create a microhabitat that supports communities that are distinct from those of the wider alleyways. 18. Large quadrats, or larger numbers of small quadrats, will be required in crops where ground vegetation is sparse or heterogeneous. The preferred option is probably more small quadrats, allowing more meaningful calculation of species frequencies. 19. Botanical methodologies must also take account of edge effects and other potential causes of transitional change in species composition across a cropped area. 3 20. Samples must be large enough, and suitably stratified, to calculate (or at least allow for) effects of geographical/climatic variation, crop species/varieties, crop density and layout, different management systems, plantation age and stage in the rotation, previous land-use and adjacent/nearby land-uses or habitat types. Invertebrates 21. Native willow species - which include common osier (Salix viminalis), a parent of most commercially available SRC willow varieties - support a great diversity of invertebrate species. 22. Most surveys and research in the UK have, however, focused on leaf beetle species that are significant pests of SRC crops. The blue willow beetle, in particular, is very widely distributed in willow SRC crops and is often present at very high densities. The brassy willow beetle and a sawfly species (Nematus melanaspis) are sometimes abundant In poplar SRC. 23. One survey, in the UK and Ireland, recorded invertebrates from 48 taxonomic groups on the foliage of SRC crops. Willows had a greater diversity of species and more individual invertebrates than poplars. 24. Another study, at five sites in southern England, recorded 21 species of conservation concern – including species of beetle, fly, spider, sawfly, alderfly, bee and wasp. Ground beetle (Carabidae) species diversity and total catches (in pitfall traps) declined as SRC plantations aged. Species assemblages for ground beetles, rove beetles (Staphylinidae) and spiders (Arachnidae) also showed a change from those of agricultural or ruderal habitats towards those more typical of less disturbed habitats. 25. Willow flowers may provide an important source of pollen for bumblebees and other insects in early spring. 26. Standard invertebrate survey methods suitable for use in bioenergy crops might include: soil sampling (soil-dwelling species e.g. earthworms), pitfall trapping (soil surface species e.g. adult beetles, spiders and ants), beating (species on crop foliage and stems e.g. spiders, true bugs, leaf beetles, butterfly and moth larvae), water traps (flying insects e.g. adult flies and sawflies) and direct searches (species under rocks, in leaf litter or at base of tree stems/stools). 27. Methods employed in previous surveys of SRC in the UK have included stem beating, pitfall trapping, direct searches of plant stems and foliage, and counts of earthworms by soil sampling or application of an irritant chemical to the soil surface. 28. The use of cumbersome equipment, such as a D-vac suction sampler, is likely to be very difficult in SRC and Miscanthus crops. Ground vegetation would be more easily sampled by sweep netting. 29. Although positioning of collection sheets will be restricted in SRC, stem beating is considered a good method for the sampling of many foliar invertebrate groups. It is, however, not considered feasible in Miscanthus crops. Leaf sampling from the upper canopy, for direct examination, will be more difficult when crops are taller than 2 m. 30. Digging large soil pits (e.g. for earthworms) may be restricted by dense root networks and dry soils. Installation of pitfall traps should, however, be readily achievable although re-location of traps and removal of trays of samples from plantations could be difficult, particularly in Miscanthus. 31. Water traps for flying insects (e.g. Diptera and Hymenoptera) may be more suitable than sticky traps. 4 Birds 32. The bird species present within bioenergy crops will vary according to the stage of growth. 33. Among the most commonly recorded species in willow SRC during the spring/summer are migrant warbler species (e.g. willow warbler , sedge warbler and garden warbler), reed bunting and pheasant; although in the early stages of crop development species such as corn bunting, skylark and linnet may be present. In winter, SRC is used by several species including pheasants and various thrushes, finches and tits. Several species of conservation concern have been recorded in SRC, in addition to those already mentioned. 34. Little is known about the use of Miscanthus by birds. It is likely to provide a much less important source of food for insectivorous species, but could provide a suitable nesting habitat for reed-bed species. 35. Standard bird survey methods include territory mapping (e.g. BTO’s Common Birds Census), point counts, line transects, mist netting and ringing (mark-releaserecapture). 36. Territory mapping, point counts and mist netting have all been used in surveys of UK SRC plantations. Adapted bird census methodologies have also been used to map the distribution of winter bird populations in SRC. US studies in poplar biomass crops have used a line transect method. Sand quadrats have been used to monitor the movement of gamebirds into and out of SRC plots. 37. Most of the standard bird survey techniques should be suitable for bioenergy crops, although severely restricted visibility (particularly in Miscanthus crops) in established plantations will increase the dependence on expert recognition of bird calls/song. Mist netting and ringing can only be employed by trained and licensed staff. Mammals 38. Although several mammal species have been recorded in willow and poplar biomass crops, only small mammals (mice, voles and shrews) have been properly surveyed in the UK. From the limited data available, SRC does not appear to provide a particularly good habitat for small mammals, although weedy plantations hold larger populations than relatively weed-free sites. 39. There have been no surveys of mammals in Miscanthus. 40. Standard methods for mammal surveys include total counts (e.g. deer or hares), counts of breeding sites (e.g. badgers, rabbits, foxes or squirrels), counting and mapping calls (e.g. bats), trapping (e.g. mice, voles and shrews), dung counts (e.g. rabbits, deer, foxes, otters) and feeding signs (e.g. dormice). 41. A few surveys of small mammals in SRC have been conducted in the UK. These have all used Longworth box traps, or similar, to capture live mice, voles and shrews. US studies in hybrid poplar plantations have used baited ‘snap traps’ that kill trapped animals. Bats have been surveyed using a tuneable, heterodyne bat detector. 42. Small mammal trapping, using grids or transects of live traps, will be appropriate for surveys of bioenergy crops – but must be repeated over several years, to allow for annual fluctuations in population size. Trap number and the duration of trapping periods should be sufficient to ensure meaningful data. Trapping in spring/early summer and autumn is preferred. 5 43. The abundance of canopy invertebrates may make SRC an important food source for bats, and surveys using acoustic methods (tuneable bat detector) should be encouraged. Reptiles and amphibians 44. There have been no formal surveys of reptiles or amphibians in bioenergy crops, but species observed in or near SRC plantations have included common toad (Bufo bufo), common frog (Rana temporaria) and common newt (Triturus cristatus). Most bioenergy crops are, however, unlikely to provide good habitat for amphibians. Similarly, these crops will not be suitable for most reptiles, but woodland edge/scrub species such as slow worm (Anguis fragilis) and smooth snake (Coronella austriaca) may possibly occur in and around the edges of some SRC plantations. 45. Standard survey methods for amphibian species include night-time, torchlight searches (preferably in wet weather); measurement of area/volume of frog spawn; pitfall trapping, with ring-fences or drift fences, if required; and netting or bottletrapping newts. Standard methods for reptiles include direct searches and use of refugia traps (‘tinning’). 46. The potential use of bioenergy crops by amphibians, perhaps migrating to a nearby pond, could be confirmed by night-time torchlight searches or (if it can be justified) by installing pitfall traps with drift fences. Probably more usefully, ‘tinning’ (refugia trapping) could be operated to ascertain the presence and distribution of reptile species. ‘Tinning’ should be carried out between late April and late June or between late August and late September. Recommendations 47. This review of methodologies for ecological monitoring in bioenergy crops has led to recommendations for a basic framework of techniques for future surveys and monitoring in the UK. 48. It is recommended that new UK monitoring projects in energy crops should be encouraged to adopt a standard suite of protocols (although this should not preclude originality or inclusion of additional species), and to follow 11 basic principles: i. Surveys/monitoring should, wherever possible, include a few ‘core groups’ considered indicative of overall biodiversity. These should include ground flora species, ground beetles, arboreal insects, breeding birds and small mammals. The list of core groups should be short, but a secondary list should be published, for measurement where resources allow. This list should include soil fauna and might also include butterflies, moths, bats and deer. ii. Surveys must not focus solely on groups for which bioenergy crops are known to provide valuable habitats. An ‘independent’ and wide-ranging approach is necessary, although it is important to monitor usage of energy crops by species of conservation concern e.g. Biodiversity Action Plan species. iii. Methodologies should be based upon widely accepted techniques - preferably those ‘tried and tested’ in surveys of bioenergy crops. For the core groups suggested above, plant frequency counts, pitfall trapping, stem beating, bird censuses and live-trapping in Longworth box traps are considered suitable. iv. Methods used must fully consider the practicalities of sampling/recording within the bioenergy crop concerned. Protocols must allow for row spacings when specifying the location of recording/sampling positions, and should consider 6 restrictions on access and movement, limited visibility in spring and summer and potential difficulties in digging soil pits. v. Surveys should be designed to facilitate valid and dependable statistical analyses. This will require care in selection of sample sites and levels of stratification, and consideration of the use of ‘controls’ - as well as robust field methodologies. Samples should be representative and take account of important influences such as climate, altitude, soil type, adjacent land-uses and plantation size. vi. New surveys should make full use of any opportunities for comparisons with ‘baseline data’ – either newly collected or already available. vii. Methodologies should, where applicable, be compatible with those used by national surveys or national environmental monitoring networks. viii. Surveys should, wherever possible, allow direct comparisons between the biodiversity of energy crop plantations and other habitats within the local landscape – particularly the land-use that it has replaced. ix. Survey plots must incorporate field margins and field boundaries. Grassy headlands might provide much of the site’s biodiversity. One important impact of bioenergy crops may result from removal of the negative effects of agrochemicals and livestock on hedgerows and watercourses. x. Surveys should also consider the wider, landscape-scale impacts of biomass crops on farmland ecology – taking account of adjoining and nearby habitats, and linkages with semi-natural habitats, and potential species movements across the landscape. xi. One-off surveys have a value, but it is always desirable to repeat surveys over at least three years, to allow for temporal changes. Populations of many species change dramatically from year-to-year, as a result of climatic factors, food availability, predator-prey interactions, etc. 7 1. INTRODUCTION 1.1 Objectives and scope The main objectives of the project documented in this report were: To review methodologies used for ecological monitoring in short rotation poplar and willow, and other biomass crops. To recommend standardised methods for future projects. Consideration of suitable methodologies for ecological surveys in biomass, or bioenergy, crops requires not just a knowledge of methods used in previous studies but also a comprehensive overview of standard assessment methodologies and a detailed understanding of the habitats concerned and the plant and animal communities within them. These aspects are, therefore, also fully reviewed. Although other bioenergy crops are mentioned within the report, the focus of the review is on short rotation coppice (SRC) and Miscanthus. Other crops are either of relatively minor importance as potential sources of renewable energy in the UK or are, as in the case of whole-crop cereals, conventional agricultural crops grown under a slightly modified production system. 1.2 Biomass crop production Concerns about the effects of global warming have led to international agreements to reduce consumption of fossil fuels and the resultant emissions of carbon dioxide – one of the most important of the ‘greenhouse gases’. Renewable energy technologies, including the use of biomass crops to fuel heat and electricity generators, are a vital component of strategies to achieve these reductions. Crop residues, such as cereal straw and forest thinnings, may provide important sources of fuel, but dedicated biomass crops will also be necessary. Although the renewable energy industry in Europe is still in a relatively early stage of development, the most important biomass (or bioenergy) crops at present are short rotation coppice willow (Salix spp.) or poplar (Populus spp.); Miscanthus grass; and whole-crop cereals. Other potential crops include energy grasses such as reed canary grass (Phalaris arundinacea), switchgrass (Panicum virgatum) and giant reed (Arundo donax). The agronomy of SRC, or arable energy coppice, has been described in detail by Britt et al. (1995) and several other authors. However, as the physical structure of bioenergy crops, the composition and density of associated vegetation, and the frequency and timing of harvesting and other management operations all have a major influence on the diversity and ecology of species within these crops, a short description of crop agronomy is considered appropriate. 8 1.2.1 Agronomy of short rotation coppice SRC crops are usually mixtures of 3-6 varieties (clones) of high yielding willows (Salix viminalis or S. viminalis x schwerinii hybrids) or poplars (Populus trichocarpa, or P. trichocarpa x deltoides or P. deltoides x nigra hybrids). They are mechanically planted in March or April, as unrooted cuttings. Willows are usually planted at densities of 12-20,000 cuttings per ha and poplars 10-12,000 per ha – in double rows, that can be straddled by a large mechanical harvester. Spacing between rows is usually 0.8 to 1.5 m. Weeds are controlled by pre-planting cultivations, pre-and post-planting herbicides and by the competition and shading from the dense crop. Crops are mechanically harvested, using heavy adapted forage harvesters, in the winter months, every three years (occasionally two or four year rotations are used). Well managed SRC crops may be over one metre tall by June in the planting year, and two to three metres tall by October. In subsequent years, after cut-back or harvest, growth can be even more rapid. At harvest, crops may be 5-7 m tall. The effects of residual herbicides and the dry, shady conditions beneath SRC crops result in a sparse and species-poor ground flora in most crops. 1.2.2 Agronomy of Miscanthus Miscanthus crops are planted as rhizome pieces, or occasionally as micropropagated plants. As for SRC, crops are planted into weed-free cultivated soil in early spring. The densely planted crops grow very vigorously and rapidly cover the ground, suppressing ground vegetation. Like SRC, Miscanthus crops are perennial, but one important difference is that Miscanthus crops are harvested annually. Crops are mechanically cut in the winter months, after the onset of dormancy and desiccation of the foliage. In spring, plants quickly re-grow from the crowns – reaching heights of 3-4 m by autumn. 1.3 Environmental impacts of biomass crops 1.3.1 Greenhouse gases The substitution of renewable biomass crops for fossil fuels in the generation of heat or electricity, if undertaken on a major scale, will bring important, and fairly obvious, environmental benefits. For example, it has been calculated that every hectare of short rotation woody energy crops, grown as a direct substitute for coal, could displace 5.2 tonnes of fossil carbon in CO2 per annum (Graham et al., 1992), as well as reducing air pollution from SOx and NOx emissions (Graham et al., 1995; Muskett, 1996). There are also other, more direct, effects on greenhouse gas emissions when bioenergy crops are grown on agricultural land. For example, Börjesson (1999) stated that “greenhouse gas emissions from arable land can be reduced in three different ways when annual crops are replaced by perennial energy crops, through 9 (i) accumulation of soil carbon in mineral soils, (ii) reduced carbon dioxide emissions from organic soils, and (iii) reduced nitrous oxide emission caused by the use of fertilisers.” If livestock numbers were to be reduced, to accommodate an increased area of bioenergy crops on grassland, then methane and ammonia emissions would also be reduced. However, the picture is not always clear. Zemanek & Reinhardt (1999) used ‘life cycle assessments’ to compare biofuels and fossil fuels, and to make comparisons between the relative values of certain biofuels. For example, their comparison of short rotation forestry (SRF) woodchip with fuel oil in a heating plant led them to conclude that SRF use saved ‘finite primary energy’ and reduced the ‘greenhouse effect’ (emission of fewer CO2 equivalents); whereas fuel oil produced fewer emissions of NOx, SO2 equivalents (responsible for acidification) and total N (responsible for eutrophication). Use of a system of weighting of factors for ecological significance, produced a final assessment in favour of the biofuels. Comparisons between biofuels led Zemanek & Reinhardt (1999) to the conclusion that cultivated solid biofuels were best if the main objective is to reduce emissions of greenhouse gases, or to reduce primary energy consumption. Furthermore, they rated SRF woodchip as “clearly the best” among cultivated biofuels. Liquid biofuels were considered to compare badly to solid biofuels. 1.3.2 Ecological impacts Their physical structure, rapid growth rates and the way that they are grown (i.e. at close spacings, with chemical weed control, fertiliser applications and regular harvests) mean that the habitat within bioenergy crop plantations is not generally favourable for plant and animal diversity (Beaumont, 1993; Britt et al., 1995). However, as these crops usually replace species-poor agricultural monocrops, of cereals or perennial ryegrass (Lolium perenne), provide a contrasting habitat, and are managed with relatively low pesticide inputs (Sage, 1998), they can increase biodiversity at the landscape scale (Beaumont, 1993; Paine et al., 1996; Perttu, 1999). The structure of SRC crops is similar to that of young traditional coppice plantations (Sage & Robertson, 1994), which frequently support large and diverse bird populations. There may also be opportunities to enhance the biodiversity of bioenergy crops through the introduction of woodland ground flora species (Tucker et al., 1997), although the additional costs and probable incompatibility with routine management are likely to severely restrict such practices. In many cases, even though biodiversity within SRC and energy grass crops is limited, the wide grass headlands (usually 6 m and 12 m) may have greater wildlife value. With appropriate management for botanical and invertebrate species diversity, these headlands could potentially provide a useful habitat for a number of vertebrate species, including several declining farmland birds. There are numerous willow species native to the UK, including the common osier, Salix viminalis, which is a parent species of most commercial SRC willow varieties. Two poplar species are also native. Black poplar (Populus nigra ssp. betulifolia) occurs naturally across most of England and Wales, and aspen (Populus tremula) throughout the British Isles (Stace, 1991). Several poplar hybrids and basket willow clones have also been cultivated here for many years. 10 Most willows support a large number of invertebrate species (Kennedy & Southwood, 1984), including many actual or potential pest species (Sage, 1994). Populations of invertebrates in SRC canopies can also be relatively large and diverse, resulting in a habitat that is attractive to insectivorous birds and, possibly, bats (although there is currently no direct evidence to support this assumption). In contrast to SRC, Miscanthus species are recent introductions from Asia and very few invertebrate species feed on this crop. Similarly, some other non-native ‘energy grasses’ being considered for cultivation in the UK (e.g. switchgrass, Panicum virgatum, and giant reed, Arundo donax) are likely to support relatively few phytophagous invertebrate species. The location of biomass crops relative to other habitat types and land uses can also strongly influence biodiversity within those crops - and their contribution to biodiversity on a landscape scale (Christian et al., 1994; Graham et al., 1996). Woody energy crops such as willow or poplar SRC, if planted adjacent to existing woodland or forest, can increase the extent of the ‘forest habitat’ and may provide corridors between fragmented woodland patches in agricultural landscapes (Graham et al., 1996). On the other hand, any ecological benefits of planting biomass crops must be weighed against the negative impacts e.g. destruction of existing habitat, removal of food resources, etc. Agronomic methods and the intensity of management will heavily influence biodiversity within biomass crops (Perttu, 1999), with less intensively managed, weedy crops generally having more plant and animal species and larger populations. Any major deviation from the ‘standard’ systems of crop agronomy, as briefly outlined in Section 1.1 of this report, is likely to have significant impacts on biodiversity value. For example, McLaughlin & Walsh (1998) have pointed out that cutting switchgrass crops twice per year, instead of annually, could have negative impacts on nesting birds. 1.3.3 Other environmental impacts Börjesson (1999) has summarised a number of other potential environmental gains when willow SRC crops replace annual arable crops. These include reduced nutrient leaching, reduced soil erosion (by water and wind), uptake of heavy metals and increased soil organic matter. Börjesson (1999) also reviewed the potential use of SRC in the treatment of municipal wastes – waste-water, sewage sludge and landfill leachate. 1.4 Objectives of ecological surveys and monitoring The objectives of any ecological survey or monitoring may vary in different situations, but it is vitally important that these are clearly determined at the outset and that appropriate sampling procedures and methodologies are selected. KovacsLang & Simpson (2000), discussing reasons for ecological monitoring, stated that “Monitoring systems provide users with information about the state of… biological resources; trends of natural changes; and effects of human interventions on 11 populations, communities and landscape mosaics. Data from monitoring can be used to assess priorities for conservation, for land use, for environmental impact assessments, and for informing policy-makers and the general public on the state of biodiversity and the environment.” Sutherland (1996a) sets out a number of general objectives that might apply to ecological studies: 1. Describing the interest of sites e.g. for the identification of those sites within an area that have the greatest biodiversity or conservation value. 2. Estimating population size e.g. to estimate the numbers of a given species within an area, or even to estimate the total population size. 3. Monitoring population changes e.g. for the determination of annual changes in the population of a particular species. 4. Determining the habitat requirements of a species e.g. comparisons between various attributes of habitats with and without the species of interest, to determine particular characteristics associated with success of that species. 5. Determining why species have declined e.g. comparisons between sites where a species still occurs and sites where it is known to have disappeared; estimation of fecundity, seedling/juvenile or adult survival; measurement of limiting factors. 6. Monitoring habitat management e.g. use of experimental designs (including replication, randomisation and use of control treatments) to measure the impacts of management practices. 7. Population dynamics e.g. annual counts to allow estimation of the population size. If estimates of population size are combined with measurements of key ‘life history parameters’ then the causes of fluctuations in population size might be deduced. All of these objectives may be applicable to studies within, or incorporating bioenergy crop sites. Describing the interest of sites is, however, probably most applicable to surveys that aim to describe the relative importance of SRC and Miscanthus crops within the wider agricultural landscape, and to compare their biodiversity with that of other farm crops and with semi-natural habitats. 12 2. ECOLOGICAL MONITORING 2.1 Practical considerations The methodology and sampling strategy will be largely determined by the scientific objectives of the research, survey or monitoring programme and will also be constrained by resource availability. There will also be important practical considerations, with certain ecological monitoring methodologies being generally unsuitable for use in biomass crops, because of difficult access, movement or vision. Biomass crops such as willow and poplar SRC and Miscanthus are usually very densely planted crops. They may quickly become difficult to walk through and some may be almost impenetrable by late summer. Certainly, in SRC, movement across rows can be severely impeded. Their rapid rates of growth mean that biomass crops commonly attain heights above the sight line of most surveyors (1.51.8 m) quite early in the growing season. These restrictions on visibility and movement make some ecological assessment methods impractical. Transects through crops may be difficult or impossible to walk, particularly if they cross crop rows. Visual detection and accurate identification of animals on either side of the transect may not be possible, particularly when surveying small, highly mobile species in very dense biomass crops during the summer months. The placing of quadrats may be very difficult for vegetation recording. If they are to be used, careful consideration needs to be given to quadrat size, positioning and whether they need to have a frame that can easily assembled and dismantled in the field. Random positioning is unlikely to be feasible. Fixed markers (e.g. for the ends of transects, or corners of quadrats or grids) may prove difficult to relocate. Horizontal measurements, by whatever method (e.g. pacing, tape measure, pedometer, hodometer) are likely to be very difficult and, consequently, inaccurate. However, as most biomass crops will have been mechanically planted at fairly accurate spacings, distances along lines running parallel to crop rows, or at 90o across rows, may be reliably estimated by counting the number of stools/crowns passed or rows crossed, respectively. It will be difficult to move through biomass crops carrying heavy and bulky equipment. This may restrict or prevent use of equipment such as D-vac suction samplers. Vehicular access beyond crop headlands will not be possible, except in the first few weeks after planting and in the period between crop harvest (during winter) and early May. 2.2 Ecological monitoring programmes and networks Ecological monitoring in energy crops has focused almost exclusively on SRC and primarily on three biological groups: plants, arboreal invertebrates and birds. UK studies undertaken by the Game Conservancy Trust, ERM (Environmental Resources Management), CSL (Central Science Laboratory) and other 13 organisations, have employed a range of methods – largely based upon standard techniques, described by Southwood (1978) and Sutherland (1996a). These techniques have included the use of quadrats for the estimation of plant species frequency and % cover in the ground vegetation; beating of stems for collection of invertebrates in the crop canopy; and census and point count methods for assessment of breeding and over-wintering bird populations. Other animal groups have been studied to a lesser degree. These include small mammals, surveyed using standard live-trapping, mark-recapture methods; and bats, monitored using acoustic methods (tuneable bat detector). Occasionally, researchers have developed novel techniques for monitoring of animal activity in and around energy crops. One example of this is the use of sand quadrats for the recording of partridge and pheasant footprints, on the edges of coppice plantations. Previous studies have provided a good insight into the ecology of SRC, but more work is required to broaden our understanding of SRC habitat use – and the ecological function of SRC crops within the broader landscape. Studies on the ecology of Miscanthus crops are also urgently needed. In the longer term, if research suggests that other grasses might be potentially viable bioenergy crops, then the impacts of planting crops such as Phalaris, Phragmites and Arundo on farmland biodiversity will also require full evaluation. Studies of the ecological effects of modified cereal management for biomass production (‘whole crop’ cereals), for example potential reductions in fertiliser and agrochemical inputs, would be useful – although much can probably be deduced from the many agricultural research projects on a similar theme. 14 3. PLANTS 3.1 Botanical species diversity in biomass crops The ground flora of SRC plantations established on ex-agricultural sites tends to be dominated by a small number of competitive or ruderal weed species, such as those typical of disturbed ground. In dense, well-managed plantations, ground cover will be sparse and shade-tolerant species relatively important. In poorly managed plantations, where early weed control has been deficient, cover can be very high and open-ground species predominant. Few species of significant conservation value are likely to be found, although rare or declining arable plants may persist (Coates & Say, 1999). Surveys of 29 SRC plantations across the UK and Ireland in 1993 (Sage et al., 1994), and a re-survey of 21 of the same sites in 1996 (Sage & Tucker, 1998a), indicated that the composition of the ground flora was largely dependent upon factors such as age of plantation, previous land use, crop management and the proximity of existing woodland. The ground flora of most SRC plantations were classified as either tall herb or ruderal communities, although there was a marked increase in the proportion classified as woodland communities in 1996 (Sage & Tucker, 1998a). The most frequently recorded species was common nettle (Urtica dioica); followed by creeping buttercup (Ranunculus repens), creeping thistle (Cirsium arvense), cleavers (Galium aparine), broad-leaved willowherb (Epilobium montanum), broad-leaved dock (Rumex obtusifolius), bramble (Rubus fruticosus agg.), rough meadow-grass (Poa trivialis), spear thistle (Cirsium vulgare), rosebay willowherb (Chamaenerion angustifolium), annual meadow-grass (Poa annua), dandelion (Taraxacum officinale agg.), groundsel (Senecio vulgaris), Yorkshire fog (Holcus lanatus), curled dock (Rumex crispus), fat hen (Chenopodium album), soft rush (Juncus effusus) and prickly sow-thistle (Sonchus asper). In the three year interval between surveys, there was a sharp decline in the frequency of rosebay willowherb and perennial rye-grass and increases in some ruderal species, such as wavy bittercress (Cardamine flexuosa) and scentless mayweed (Tripleurospermum inodorum). There were also apparent increases in the frequency of ivy (Hedera helix) and elder (Sambucus nigra) and grasses such as annual meadow grass, creeping bent (Agrostis stolonifera), common bent (A. tenuis), creeping soft-grass (Holcus mollis), couch (Elytrigia repens) and tufted hair-grass (Deschampsia flexuosa) – although most of these species were still recorded at only a small number of sites. Sage & Tucker (1998a) also reported that plant species more characteristic of woodland or woodland edge habitats were more frequently recorded in western SRC sites, where landscapes were generally more wooded. Coates & Say (1999), in a survey of five young SRC plantations in England, found that the ground flora was dominated by semi-ruderal species. The extent of ground cover varied greatly, from 0-15% where the crop canopy was closed to 100% in very sparse, open crops. In the more open crops, docks (Rumex spp), thistles (Cirsium spp.) and common couch tended to dominate. Where crop cover was more comprehensive, common nettle and rough meadow-grass were the most frequently recorded species. Shade-tolerant willowherbs (Epilobium spp.) were a 15 constant and locally dominant feature of the ground vegetation. Over the first six years of the cropping cycle, there was a sharp decrease in annual ruderals and a tendency for woodland and marsh species to increase. Surveys in Swedish willow SRC plantations have recorded 125 vascular plant species and 18 mosses (Gustavsson, 1987; cited by Börjesson, 1999). This compares with a typical 50 weed species in Swedish cereal crops, of which about 30 occur only sporadically (Börjesson, 1999). The results of surveys in England (Coates & Say, 1999) and Sweden (Börjesson, 1999), clearly illustrate the influences of site management and previous and adjacent land uses on ground flora composition – and demonstrate the importance of carefully documenting such factors. Coates & Say’s results were undoubtedly affected by inconsistent management regimes and the fact that several plots remained unharvested throughout the survey period. Significantly, one site (in Oxfordshire) was adjacent to the River Thames and had two nearby ponds and another (in Cornwall) had woodland on three sides of the plantation, with several nearby ancient semi-natural woodland sites (including an SSSI). These two SRC sites accounted for much of the recorded increase in marsh and woodland species respectively, within the sample of sites as a whole. Neither was managed according to normal guidelines. For example, neither site received fertilisers and the Oxfordshire site was not sprayed with herbicides. The Cornish site, which was predominantly poplar, was planted at a relatively low density. Both of these sites were cut back after the first year, but neither was subsequently harvested (although the Cornish site was partially thinned with a chainsaw). The surveys mentioned previously have all focused on botanical diversity within bioenergy crops. For various reasons, already described, the ground flora beneath SRC or energy grasses is usually of limited ecological value. In many instances, the relatively wide grassy headlands maintained around bioenergy crops will be significantly more diverse. Consequently, it is important that botanical monitoring also includes crop edges and headlands. 3.2 Standard botanical survey methods Plant species diversity may be simply measured by compiling a list of all species found across a site, or within one or more sample plots. Although this information can be interesting and provide a good indication of a habitat’s ‘conservation importance’ relative to other habitats, it is usually necessary to collect data that provide a measure of the relative prominence of individual species within the sampled vegetation. This is usually achieved through assessments of cover, biomass or frequency (Bullock, 1996). Although the sedentary nature of most plants makes them easier to observe than most animal species, it is important to remember that most are very different in appearance, size and visibility at different times of year. Careful thought must be applied to the choice of survey period and repeat surveys at different times of year are frequently advisable (e.g. surveys in May and August). At certain times of year, 16 some species will be difficult to identify reliably. Other species have no aboveground organs for part of the year. Estimates of cover Cover is usually defined as the percentage of an area covered by the above-ground parts of a plant if viewed directly from above. As the foliage of plants overlaps, the total percentage cover can, and very often does, total more than 100. The proportion of ground covered by individual plant species within frame quadrats or across the whole site can be visually estimated. An estimate of percentage cover can be assigned to each species present, or some sort of scale (either existing or devised specifically for the task in hand) might be used. Percentage cover can also be assessed using point quadrats, which are particularly useful for assessments in grasslands and other short vegetation types. These provide a more objective measure of percentage cover, as only the species that are in direct contact with the vertical metal pin (or other ‘point’) are recorded, with no requirement for visual estimates of relative cover percentages. However, the use of point quadrats is very time consuming because a very large number of points is needed to obtain an accurate record of infrequent species. The simplest scale in frequent use is the DAFOR scale. Using the DAFOR system, plant species are subjectively classified as ‘dominant’, ‘abundant’, ‘frequent’, ‘occasional’ or ‘rare’ – although each class has no strict definition, or associated range of percentage cover values, and depends on each surveyor’s interpretation. Alternatively, researchers can devise their own percentage classes or use widely accepted systems such as the Domin or Braun-Blanquet scales (Table 1). The main advantage of visual estimates of cover is speed. However, there are several disadvantages, including subjectivity and difficulties in accurately estimating cover percentages – particularly for tall vegetation that you cannot look down on from above. The most reliable estimates can be obtained when low vegetation within a quadrat is viewed directly from above. In most instances, the use of very narrow ranges of percentage cover (e.g. 5% or less) probably cannot be justified by the achievable accuracy of the recorder’s estimates. Although the Domin scale has often been used in surveys, it is of very limited use in scientific studies. It is a quick technique, for use in the field when available time is very limited, but data collected are non-linear and difficult to analyse. It is possible to convert Domin scales to percentage cover values, but there are advantages in simply estimating cover in the first instance. Data from plant cover estimates of this type are scores and should only be analysed using non-parametric statistical techniques (Bullock, 1996). The accuracy of cover estimates for ground flora can be increased by training staff and by providing calibrated ‘templates’ for standard amounts of cover (i.e. small sub-quadrats representing a known proportion of the total quadrat area). As visual cover estimates are, however, subjective it is also important to maintain consistency, both between assessors and between different occasions e.g. repeat 17 surveys. Wherever possible, repeat surveys should be undertaken by the same individuals involved in the previous survey. Teams of assessors should mutually calibrate at regular intervals (e.g. once every two or three days for lengthy surveys), by assessing one or two quadrats jointly, to ensure continued consistency between them. Table 1. Domin and Braun-Blanquet scales for visual estimates of plant cover (from Bullock, 1996) Value + 1 2 3 4 5 6 7 8 9 10 % cover or other description Braun-Blanquet Domin < 1% 1-5% 6-25% 26-50% 51-75% 76-100% 1 individual, with no measurable cover < 4%, with few individuals < 4%, with several individuals < 4%, with many individuals 4-10% 11-25% 26-33% 34-50% 51-75% 76-90% 91-100% Biomass The above-ground biomass of plants can be readily calculated by harvesting (cut flush with, or close to, the soil surface) and weighing. Normally, this involves cutting the base of all plants within a quadrat, putting the cut plants into polythene bags (to conserve moisture) and returning them to the laboratory for weighing. If necessary, plants can be oven dried, for the determination of dry weight as well as fresh weight. Dry weights are always preferable (Bullock, 1996). Samples can be weighed whole – to calculate the total plant fresh/dry weight per unit area – or subdivided first (before drying) into species or species groups (e.g. grasses and forbs). Sorting harvested material can, however, be very difficult, particularly if plants fall apart after cutting. Large samples may be weighed whole and sub-sampled in the field, and the subsamples taken to the laboratory for botanical separation and/or dry weight percentage determination. Attempts to measure the biomass of roots and other underground organs are made much less often in ecological studies and are more usually restricted to studies of plant physiology. Measurements of biomass involve destructive sampling and should not normally be used in areas of high conservation value – unless the scale of sampling is really of no consequence. This is unlikely to be an issue, however, in bioenergy crops. 18 Frequency The frequency of occurrence of any plant species can most simply be measured as the percentage of quadrats in which that species was recorded. Quadrats might be distributed across the survey area in either a random or non-random fashion (e.g. on a grid or along transects). One alternative is to use quadrats that have been subdivided into smaller squares and, for each species present within the quadrat, to record the number of smaller squares in which that species was present. For example, a 0.5 x 0.5 m quadrat might be sub-divided into 25 squares of 10 x 10 cm. A development of this approach involves the use of ‘nested’ quadrats, each nest containing a series of cells of increasing size (Hodgson et al., 1993). Each species present is recorded against the cell number in which it first occurs, with the higher numbers representing the largest cells. Consequently, dominant species will tend to have a high proportion of 1 and 2 scores. This approach has been further developed into the ADAS Plot Method (Critchley & Poulton, 1998; Burke & Critchley, 1999; Critchley et al., 2002) which has been widely used in the monitoring of the impacts of UK agri-environment schemes. This method uses a number of nested quadrats placed together at a site in a single block or ‘plot’. A location for the plot is chosen as representative of the site as a whole. Data are analysed in a way that combines objectivity with a high level of sensitivity for detecting vegetation change. Use of nested quadrats per se effectively minimises variation between recorders, a very important consideration in national surveys or monitoring programmes involving several ecologists. However, one disadvantage of the ADAS Plot Method is that its complexity and intensity of measurement mean that it can be relatively costly to implement. Vegetation mapping This involves the classification and mapping of vegetation communities, either into broad categories based on simple characteristics observed in the field or by statistical ordination of species data. One widely used system of vegetation mapping using broad habitat categories is English Nature’s Phase 1 Habitat Survey. An example of the more complex type of vegetation classification is the National Vegetation Classification (NVC) e.g. Rodwell (1991 & 1992). 3.3 Botanical survey methods applied in studies of biomass crops The Game Conservancy Trust’s surveys of SRC sites in the UK and Ireland (Sage et al., 1994; Sage, 1995; Sage & Tucker, 1998a) used linear quadrats for assessments of the abundance of all higher plants within each quadrat. In each surveyed SRC plot, five 10 x 1 m quadrats were randomly positioned in the alleyways between crop rows. These relatively large quadrats were used to ensure that all of the more frequently occurring species were recorded – even in plots where the ground vegetation was very sparse. Linear quadrats were used to avoid the need to position quadrats and record vegetation across tree rows, which would be more difficult and time consuming. Another concession to time/cost restrictions was the omission of bryophytes from the species recorded. All plants recorded were assigned an abundance ‘score’, based on a slightly adapted DAFOR system 19 (see Section 3.2), with the addition of a ‘V’ category for very rare species that were estimated to cover less than 1% of the total quadrat area. ‘Rare’ species covered 15% of the quadrat, ‘occasional’ species 5-10%, ‘frequent’ species 10-25%, ‘abundant’ species 25-50% and ‘dominant’ species 50-100%. Data were analysed using TABLEFIT (Hill, 1996), to assign plant communities to NVC types, and DECORANA (detrended correspondence analysis) (Hill, 1994) programmes. DECORANA allowed the vegetation communities of different sites to be plotted on a single scatter graph (ordination diagram), and the similarities between different sites to be viewed pictorially – those with strong similarities being plotted close together. Sage & Tucker (1998a) also classified ground vegetation at different sites according to the primary ecological strategies of the dominant species present. The ecological strategies of individual plant species were determined as ‘competitor’, ‘ruderal’ or ‘stress-tolerator’ (or an intermediate category) according to the system devised by Grime et al. (1988). In their studies of five SRC sites in southern England, ERM (Coates & Say, 1999) also used linear quadrats. The main differences from the methods used by Sage et al. (1994) were that quadrats were smaller (4 x 1 m); located permanently on a grid, rather than randomly, so that the same quadrats could be assessed annually for six years; and located in adjacent field edge, hedgerow and farmland habitats, as well as SRC. Noticeable differences in botanical species composition can be expected along a gradient from the crop edge towards the centre. This will be due to decreasing light levels and wind exposure - and probably also soil moisture – along this gradient, combined with increasing distance from adjacent habitats that may provide sources of incoming propagules. This effect has been extensively documented in woodland and forests (as well as many other habitats, including arable fields and set-aside) and many botanical surveys have utilised methodologies that were designed to measure the effects of distance from the field or woodland edge. For example, Buckley et al. (1997) placed 1 x 1 m quadrats at intervals along transects that ran from a woodland ride into the woodland, spanning all of the expected vegetation zones. A survey of hybrid poplar plantations in four countries (Britt, 1999; Weih et al., 2003) also used quadrats spaced at pre-determined distances along transects running from the woodland edge into the plantation. Similar transects ran from the edges of adjacent or nearby agricultural fields, to collect comparative data on the floral composition of fields that had not been planted with poplars. Plant frequencies were assessed using nested quadrats. A 0.25 m2 (0.5 x 0.5 m) frame quadrat was sub-divided to allow each species within it to be assigned a score of 14, where 1 was allocated to the species (or other cover variable e.g. leaf litter) directly beneath a point in one corner of the quadrat. Scores of 2, 3 or 4 were then given to all additional species that first occurred within the 10 x 10 cm, 25 x 25 cm or 50 x 50 cm sub-divisions of the quadrat. 20 3.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops Any methodologies used for surveys of the flora within biomass crops must take full account of the physical difficulties of placing quadrats across crop rows and the distribution of ground vegetation – as well as the scientific objectives of the research and the proposed methods of statistical analysis. The use of large quadrats, or a large number of smaller quadrats, may be required in biomass crops where ground vegetation is sparse or particularly heterogeneous. The relatively large, rectangular quadrats (10 x 1 m) used by the Game Conservancy Trust (Sage et al., 1994; Sage, 1995; Sage & Tucker, 1998a) allow ready placement between pairs of rows in SRC crops and ensure inclusion of a representative range of species, even in very sparse vegetation. Such large quadrats are, however, quite difficult to work with and accuracy of recording can be lower than when working with smaller quadrats. The smaller, rectangular quadrats (4 x 1 m) employed by Coates & Say (1999) probably offer a better compromise between the advantages of many small quadrats and the need for larger quadrats when surveying low density ground vegetation. Both of the above, however, lend themselves primarily to the compilation of species lists and subjective estimates of percentage ground cover and relative species abundance scores (e.g. DAFOR, Domin or Braun-Blanquet). The use of nested quadrats and their placement at pre-determined intervals along transects running from the headland or crop edge into the biomass crop, as used by Britt (1999) and Weih et al. (2003), provides more objective data for analysis of relative species frequencies and allows measurement of edge effects, which can be very important. To ascertain the true floral diversity of a biomass crop, measurements should not be confined to the most easily accessible areas e.g. between twin-rows of SRC. Surveys restricted to the larger alleyways (often 1.5 m wide) between pairs of rows are relatively simple, and therefore relatively quick and cheap. However, there is a danger in this approach in that some species prevalent in areas adjacent to tree stems/stools might be under-represented or omitted from the survey sample. It seems likely that plant communities in areas closer to crop plants will differ from those in the wider alleyways – due to reduced disturbance and, possibly, to lower light, soil moisture and nutrient levels – although there is currently no evidence to support this assumption. It is also very possible that certain species (e.g. some bryophytes) may be present only within the microhabitat provided by tree stem bases. Large quadrats can incorporate intra-row, as well as inter-row, ground vegetation, but they would have to be of a type that can be easily constructed in the field, around crop plants. For all situations where taller, or woody, vegetation is likely to seriously impede quadrat positioning, fixed frame quadrats will be unsuitable. Alternatives to be considered will include a quadrat with only three fixed sides, which is slid into position around or beneath the obstructing vegetation, or pegs and string. 21 Surveys of vegetation within SRC must take account of variation between sites, by including several contrasting sites in the sample. The effects of vegetation succession, as a plantation ages, and the effects on the ground flora of rapidly changing conditions after crop harvests must also be accounted for – by repeating assessments over at least three years. Repeat assessments should be performed within quadrats placed in permanently marked positions. 22 4. INVERTEBRATES 4.1 Invertebrate species diversity in biomass crops Native willows are known to support a great diversity of invertebrate species, but most studies of the invertebrate fauna of SRC crops have focussed on pest species, particularly three species of leaf beetle (Coleoptera: Chrysomelidae): the blue (Phratora vulgatissima), brassy (P. vitellinae) and brown (Galerucella lineola) willow beetles (e.g. Kendall & Wiltshire, 1998; Sage & Tucker, 1998a & 1998b; Sage et al., 1999). Research has included detailed studies of the life cycles and ecology of leaf beetles (Kendall & Wiltshire, 1998; Sage et al., 1999) and their preferences for different species and clones (Augustin et al., 1993; Kendall et al., 1996; Orians et al., 1997). A review of the status of a wider range of actual and potential insect pests of willows and poplars was published by Sage (1994). Sage & Tucker (1997) surveyed the invertebrate fauna in the canopies of 21 SRC crops across Britain and Ireland. They recorded animals from 48 taxonomic groups, with a greater diversity of groups in willow plots than in poplars. Leaf beetles were, by far, the most abundant canopy invertebrates in poplar and willow plots – although not all invertebrate groups present were efficiently sampled by the beating method employed. Blue willow beetle was recorded in most willow plots surveyed, but not in poplar plots. Brown willow beetle was recorded on a few of the willow plots. Brassy willow beetle was recorded only in poplar plots. The total number of leaf beetles was sometimes very high – greater than 20 per m2 of crop (equivalent to 200,000 per ha) on some plots. Larvae of a sawfly species, Nematus melanaspis (Hymenoptera: Symphyta) were also abundant at one poplar site. Sage & Tucker (1997) found significantly higher numbers of individual Diptera and Heteroptera insects in willow plots. Discounting the main pest species, leaf beetles and sawfly larvae, willow plots also had a higher total number of individual invertebrates than did poplars. Male willow plants can provide a useful source of pollen for bumblebees, and other pollinating insects, in early spring (Börjesson, 1999; Reddersen, 2001); so assessment of these species will often be worthwhile. Coates & Say (1999) examined the ground-dwelling invertebrate fauna of five willow and poplar SRC sites in southern England. They trapped and identified species of ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae) and spiders (Arachnidae). There was a general decrease in species diversity and total numbers of ground beetles as plantations aged. Changes in the species diversity and total numbers of rove beetles and spiders showed no clear pattern. Species assemblages for all three groups indicated a change away from communities typical of agricultural or ruderal habitats, towards those more typical of less disturbed habitats. For example, the ground beetle Pterostichus melanarius, which is commonly present in high numbers in arable fields, rapidly declined or disappeared after SRC establishment. Coates & Say recorded a total of 21 species 23 of beetle, fly, spider, sawfly, alderfly, bee and wasp of conservation importance (i.e. Red Data Book or Nationally Scarce). Baxter (1996), in a one-year survey of three SRC sites, recorded 30 species of ground beetle and 22 rove beetles (7 unidentified). However, the actual number of species present was probably higher than this, as several were identified only to the level of genus. Slater et al. (1997) found that the ground-dwelling invertebrate assemblage in a willow SRC site in mid-Wales generally reflected that of the preceding land use (rough pasture). In some instances, populations of earthworms appear to decline when SRC is planted on agricultural land (Sage & Tucker, 1998a; Coates & Say, 1999). Comparisons of the biomass of larger invertebrates (>2 mm in length) in soil samples from SRC, rushy pasture and improved pasture (at a farm in Devon) showed that there was a significantly lower total biomass in SRC – with smaller weights of earthworms, beetle larvae (Coleoptera) and leatherjackets (Tipulidae) (Sage & Tucker, 1998a). However, in contrast to these findings, research in Sweden has suggested that the diversity and abundance of soil organisms, especially decomposers such as earthworms, wood-lice and harvestmen, are generally higher in SRC than in arable fields (Börjesson, 1999). It might be presumed that soil-dwelling invertebrates, in general, are adversely affected by drier soil conditions in SRC crops, which are known to have very high rates of water use. In their study, Sage & Tucker (1998a) demonstrated that soils under SRC had a lower penetrability than nearby rush pasture and improved pasture. These negative factors may be counter-balanced by the positive effects of reduced soil tillage, reduced agrochemical inputs and increased leaf litter/organic matter (Börjesson, 1999). 4.2 Standard invertebrate survey methods Of the many methods listed by Ausden (1996) and Consult-Eco (2000), those most widely used for invertebrate groups likely to be of major interest to researchers investigating the ecology of biomass crops are listed in Table 2 and described in more detail later in this section. If the objective of a study is to measure the invertebrate diversity at a site, or within a specific habitat – perhaps relative to another, adjacent site or habitat – then it will be important to incorporate as wide a range of methods, sampling positions and sampling times/dates as resources allow. If the aim is to confirm the presence of, or estimate the population size of, a specific species or species group, then it will be important to fully understand the specific microhabitat requirements and life cycle of the target organism(s) before a sampling methodology is confirmed. 24 Table 2. Potentially appropriate sampling/survey methods for some important terrestrial invertebrate groups (from Ausden, 1996). Species group Stage Method Direct searching Ants Bees and wasps Beetles Adults Larvae Separation from soil Water traps Light traps Soil sampling Adults Larvae Adults Earthworms Flies Adults Larvae Lacewings, ant-lion, etc Adults Moths Adults Larvae Suction sampling Adults Spiders & harvestmen Springtails Slugs and snails Woodlice & other terrestrial crustaceans Sweep netting Grasshoppers & crickets Sawflies & parasitic wasps Flight interception traps Centipedes, millipedes, etc Dragonflies & damselflies Beating Bugs Butterflies Pitfall traps 25 26 A survey of invertebrate species diversity within a biomass crop might, for example, incorporate: Soil sampling – to identify soil-dwelling species e.g. earthworms (Annelida), beetle (Coleoptera) and fly (Diptera) larvae. Pitfall trapping – to trap soil-surface species e.g. adult ground and rove beetles (Coleoptera: Carabidae and Staphylinidae); spiders (Arachnida: Araneae), harvestmen (Opiliones); ants (Hymenoptera: Formicidae) and true bugs (Hemiptera). Beating – to capture species living on plant stems and foliage e.g. spiders, harvestmen, true bugs, leaf beetles (Coleoptera: Chrysomelidae), lacewings (Neuroptera: Planipennia), caterpillars of butterflies and moths (Lepidoptera) and sawfly larvae (Hymenoptera: Symphyta). Water traps – to trap flying insects e.g. adult flies and sawflies (Hymenoptera: Symphyta). Direct searches – to find invertebrates in favoured microhabitats that might otherwise remain unsearched e.g. under rocks, in leaf litter, at base of tree stems/stools, under the bark of any dead and decaying branches. As well as for those groups shown in Table 2, direct searching can also be used for dayflying moths. The period of trapping (duration, time of day and time of year) will have a very important influence on the species and numbers of any invertebrate group captured. Many species hibernate throughout the winter months – so even if they are present, they will be inactive and will not enter traps. Many invertebrates may utilise biomass crops during one part of their lifecycle, but occupy another habitat during other parts. Even if present in the biomass crop throughout their lives, they may occupy different sub-habitats at different times e.g. larvae might be present in the soil or leaf litter, whilst adults feed in the crop canopy. Most survey methods are measures of species activity, as well as abundance. Activity is frequently very heavily dependent on factors such as air temperature, solar radiation levels, wind strength, humidity and soil moisture. Weather conditions (recent, as well as present) will also influence the location of many invertebrate species, and their likelihood of being observed or captured. For example, in wet weather, earthworms will be nearer the soil surface and molluscs are more likely to be grazing on taller vegetation; and on warm, calm and sunny days butterflies are more likely to be found in open positions feeding on flowering plants. Many standard methodologies (e.g. ‘Pollard Walk’ for butterfly surveys) take account of this by requiring that surveys are undertaken only in specified weather conditions. It is important that weather conditions during survey periods are recorded and, if it is not possible to record different sites simultaneously, that sites between which comparisons are subsequently to be made are recorded in similar conditions. Many invertebrate species are diurnal, whilst others are nocturnal. Levels of activity might be higher at dawn or dusk. Survey periods should either be extended 27 across a period of at least 24 hours, and preferably over several days, or be timed to ensure that the target species/groups are trapped or monitored during peak periods of activity. Survey methods A brief summary of each of the important invertebrate survey methodologies listed in Table 2 is given below. Direct searching Targeted searches of suitable habitats. Particularly useful for locating species that are not widely distributed across a site and are unlikely to be detected by methods that utilise random sampling, transects or trapping grids. Targeting sampling of dead wood, leaf litter, mammal dung and carrion may be the optimum method for the collection of many specialist saprophagous species. Many species, particularly those that are most susceptible to dehydration (e.g. slugs), may be found congregated under rocks, logs or dense masses of vegetation - particularly on warm, dry days. Tussocky grasses can hold large numbers of hibernating invertebrates during winter months. Large flying insects such as butterflies, dragonflies and damselflies may be identified in the field or collected using nets. Smaller insects and spiders uncovered during targeted searches may be collected using a ‘pooter’ (a simple piece of equipment for safely sucking invertebrates up through a piece of plastic or rubber tubing into a collection bottle - see Ausden, 1996) or a fine, moistened paintbrush. Grass tussocks can be cut off at ground level, taken inside and shaken onto a white surface for subsequent identification of invertebrates present. Direct searching can be standardised in some situations to obtain relative population estimates (Ausden, 1996). Examples include: Determination of the numbers of specified insects or galls on a pre-determined number, area or weight of leaves (or a number of whole plants). Data on the distribution and frequency of leaves or plants can then be used to estimate the total population of a species or group per plant or per unit area. Counts of individuals per unit area. May be performed across a defined area (e.g. a pond) or using quadrats within a selected habitat or microhabitat. Most useful for large conspicuous species (e.g. dragonflies) or relatively immobile species such as molluscs. More mobile taxa, such as grasshoppers and crickets, can be more reliably counted by placing a quadrat and then returning to it later, or by using ‘box quadrats’ with high sides to reduce lateral movement (Ausden, 1996). Counting invertebrates along transects. Useful for the estimation of the relative sizes of butterfly, dragonfly or damselfly populations through, or along the perimeters of different habitats. The effects of weather conditions on numbers of flying insects make it essential for transects to be walked in similar conditions, if comparisons are to be made between them. The best known example is the ‘Pollard Walk’ (Pollard, 1977) method, used across Britain in the Centre for Ecology and Hydrology’s Butterfly Monitoring Scheme (BMS) (Hall, 1981; Pollard et al., 1986; Sykes & Lane, 1996). The BMS methodology specifies that surveys, completed between 1 April and 29 28 September, should always be completed between 10.45 and 15.45 British Summer Time and only when the air temperature is at least 13oC and it is not raining. If the temperature is 13-17oC (or 13-15oC at northern, upland sites), then there must be no more than 40% cloud cover. At higher temperatures, the extent of cloud cover is irrelevant. Separation from soil, leaf litter or other debris Invertebrates may be separated from samples of soil, leaf litter or other debris using a variety of methods, including: Dry sieving through progressively smaller sieves (Ausden, 1996, suggests working down from a 3-4 mm to a 0.5 mm mesh sieve) onto a white cloth, under a strong light. Wet sieving with running water. Stirring the sample in a bucket of water and collecting the invertebrates that float to the surface. Beetles float readily in tap water, but the proportion of other invertebrate groups collected will be increased if the specific gravity of the water is increased by adding sugar or salt (Ausden, 1996). Small invertebrates are collected using a pipette or paintbrush. Tullgren funnel. This is a ‘desiccation funnel’ used to extract invertebrates that favour cool, damp or shady conditions from loose, large-particled substrates e.g. leaf litter (Ausden, 1996). A funnel, ‘plugged’ with a gauze mesh to prevent the substrate from falling through is filled with leaf litter or other suitable sample material. A collection bottle, containing moistened filter paper (for live specimens) or a preservative, is placed beneath the funnel and a strong light source above it. Invertebrates move downwards, away from the light source (and the warm, dry conditions that it creates), and fall into the collection bottle. Water traps Coloured bowls filled with water can be used to trap flying insects. The range of species captured will be heavily influenced by the colour of the bowl and the height at which it is placed (Ausden, 1996). Yellow plastic bowls are widely used, which are strongly attractive to flies (Diptera) and wasps (Hymenoptera). White bowls also attract Diptera, but strongly repel Hymenoptera species. ‘Neutral’ colours such as brown, grey or blue have little attractant or repellent effect on insects, reducing the selectivity of samples. The largest catches are usually obtained from water traps placed just above the height of surrounding vegetation. If comparisons are to be made between sites, then traps should be positioned at a standard height at all sites. However, if the objective is to get as broad a view as possible of the flying insect diversity at a site, traps should be located at a range of heights and locations across the site. Insects that land in the water and get trapped there should be removed at least once per week (by pouring through muslin), and transferred to sample bottles with 70% alcohol, before subsequent identifications. Alternatively, weekly samples could be oven dried and the total flying invertebrate biomass (dry weights) of different habitats compared. 29 Efforts must be made to prevent traps from overflowing with rainwater or drying out. Water traps are prone to disturbance by birds (which may eat the trapped invertebrates), cattle (which use them as drinking bowls) and, because they are so conspicuous, even humans. Light traps These depend upon the attraction of bright lights to moths and some other groups of night-flying insects (Ausden, 1996). Various types of light trap can be used, from a simple light bulb hung beside a white sheet to purpose built, mains-powered traps with mercury vapour bulbs, automatic timer-switches and integral killing jars. Traps can be set for just a few hours on one night, or remain in situ for trapping every night over a period of several years. Moths are either identified in the field, trapped alive for subsequent identification or killed with a chemical such as tetrachloroethane. Other insect groups, notably crane flies (Diptera: Tipulidae), may also be captured in significant numbers in light traps. A network of permanent moth traps is operated by the Rothamsted Light Trap Network (Rothamsted Research, Harpenden). This network includes the 12 UK Environmental Change Network (ECN) sites and the methodology used is described by Sykes & Lane (1996). Soil sampling Soil sampling is frequently used for counts of large soil-dwelling invertebrates such as earthworms, fly larvae (e.g. Tipulidae) and beetle larvae (Ausden, 1996). A known volume of soil is either dug with a spade or lifted using a soil corer. Soil samples collected are broken up by hand to reveal the invertebrate species being sought, for example earthworms or leatherjackets (larvae of Tipula spp). Alternatively, leatherjackets may be extracted from soil cores using a ‘Blasdale extractor’ (or similar equipment), which uses a heat source to force live larvae downwards into a tray of water (i.e. applying a similar principle to that used by the Tullgren funnel). This significantly reduces labour inputs when large volumes of soil have to be sorted. Smaller, more difficult to observe species can be retrieved from soil samples using a ‘wet sieve’ technique, which involves washing soil through a 2 mm sieve (Ausden, 1996). Counts of the number of organisms in a known volume of soil will allow estimation of the total number in larger soil volumes or per unit area of land on that site e.g. the number of leatherjackets per hectare of grassland. Pitfall traps Pitfall traps are small, smooth-sided traps (usually plastic cups) placed into holes in the ground for ground-dwelling invertebrates to fall into (Luff, 1975; Ausden, 1996; Sykes & Lane, 1996). Seven to 10 mm diameter cups, usually set out according to a grid or at intervals along a transect, are placed vertically in the soil, so that the rim of the cup is approximately level with the soil surface. A small 30 quantity of anti-freeze is placed in the cup, to prevent captured invertebrates from eating each other and to slow decomposition (Ausden, 1996). Anti-freeze is preferred to alcohol, because it evaporates much less readily. Invertebrates such as ground beetles, rove beetles and money spiders (Linyphiidae) moving across the soil surface fall into the trap and cannot escape. Traps are commonly left ‘open’ (i.e. without lids) in the field for periods of one or two weeks. It is important to note that the numbers of invertebrates captured in pitfall traps reflect levels of activity, as well as population size. Relatively large catches during one particular trapping period do not necessarily indicate increased abundance. Flooding of pitfall traps can be a problem during periods of heavy rainfall. This problem can be effectively eliminated by positioning a plastic plant pot saucer, on a simple wire frame, a few centimetres above the trap. Accidental trapping of small mammals and amphibians can be reduced by positioning wire mesh (e.g. ‘chicken wire’) over the top of the cup and/or as a cone placed in the bottom of the cup. Pitfall traps may also act as water traps for flying insects (e.g. Diptera and Hymenoptera), but should not be used to count numbers of these groups as catches will be heavily influenced by the colour and visibility of the traps. Beating A simple method for the collection of a wide range of invertebrates from the foliage of plants (Ausden, 1996). It is particularly useful for the collection of relatively loosely attached phytophagous (plant-eating) and predatory species - including caterpillars (of moth, butterflies and sawflies), leaf beetles and ladybirds - from branches of shrubs and small trees. It is less suitable for species that readily fly off when disturbed, although a variation on the beating method involves striking a branch and then netting the insects that fly away (Ausden, 1996). Under the standard method, a branch is struck sharply with a rod or stick, to dislodge invertebrates. These invertebrates are then collected on a cloth or ‘beating tray’ positioned on the ground, directly beneath the branch. They are then picked up using a pooter and transferred to sample bottles. Beating trays, which can either be purchased or home-made, comprise a cloth-covered tray, sloping towards the centre (Ausden, 1996). Standardisation of the methodology used - in particular the number and strength of strikes on branches, the number of branches hit and the size of the cloth or beating tray – will allow relative estimates of invertebrate numbers (Ausden, 1996). Beating is easier in young stands. In dense, older stands, it can be difficult to get a clear aim at a tree, and hitting thick stems may fail to dislodge insects in the uppermost foliage. Selecting the number of branches to hit can also be more difficult when they are growing close together. 31 Flight interception traps These involve screens of fine black netting (e.g. Dacron or Terylene) stretched across insect flight paths, to intercept flying insects. Insects that fly into the netting drop into trays of water (with a few drops of detergent, to reduce surface tension) placed immediately beneath the netting. Flight interception traps are frequently placed along woodland rides, woodland edges or hedgerows – where numbers of flying insects tend to be high. These traps are conspicuous and, consequently, prone to disturbance. Their size, and relative complexity, make replication more difficult. One variation of the flight interception trap is the Malaise trap. In these traps, the netting is used to channel insects upwards into a collecting bottle. These traps are more expensive, but are more efficient at catching smaller, more agile flying insects that are not caught in large numbers by the simpler type of flight interception trap described above (which catch larger proportions of large beetles, etc). Sweep netting This method involves passing a sweep net (which must have a metal rim) through vegetation, using alternate forehand and backhand strokes (Ausden, 1996). Vegetation should be at least 15 cm tall, dry and neither trampled nor flattened by wind or rain. As with beating, invertebrate groups that attach themselves firmly to foliage, and those that fly off when disturbed, will be under-represented in samples collected. The number, length, speed, depth and angle of sweeps through the vegetation will all influence the size and composition of invertebrate catches. Consequently, all have to be standardised and, preferably, implemented by the same surveyor if any comparisons between sites/habitats are to be made. Ausden (1996) suggests a series of net sweeps approximately 1 m in length, taken every other pace while walking at a consistent speed through the vegetation. Sweep netting may be difficult in very dense crops, if there is insufficient space to freely move the net from side to side. Suction sampling Invertebrates in low vegetation may be more effectively sampled using a suctionsampler, such as the D-vac. The D-vac is a large and heavy piece of equipment, carried on the back of the operator, which uses a vacuum to suck air into the mouth of the machine – drawing invertebrates into a fine netting or muslin sample bag secured at the inlet point. Normally, the collecting nozzle of the sampler will be held down on the vegetation (or soil surface) for a given length of time and on a pre-determined number of occasions. As the area of the collecting nozzle is known, total catches might be used to give estimates of the population of the target species or group per unit area (e.g. Collembola m-2). 32 After returning from the field, invertebrate samples can either be killed in a killing jar or stored in a deep freeze, for later sorting and identification. As for sweep netting, suction sampling is not suitable for use on damp vegetation. In contrast to sweep netting, however, it is most suitable for use on very low vegetation (height less that 15 cm) and can even be used effectively on bare soil. Suction sampling with a D-vac can be very problematic. The machines are heavy and cumbersome, so carrying them across rough terrain, over longer distances or for long periods can be very uncomfortable and may be unpopular with staff. During operation, they are also noisy and cause significant vibration. They must be regularly refuelled with a petrol/oil mixture. They are prone to mechanical breakdowns, but replacement machines are expensive. Ausden (1996) suggests that garden leaf collection machines offer a smaller, lighter alternative to purpose-built D-vac equipment. No direct comparisons between the efficiency of the two types of machine have been made. Suction samplers may under-record large species that can effectively shelter from the D-vac or which attach themselves firmly to the vegetation and those that live low down in taller areas of vegetation (Ausden, 1996). 4.3 Invertebrate survey methods applied in studies of biomass crops Many of the published studies of invertebrates in SRC crops have focussed primarily on species in the crop canopy – in particular the leaf beetles (Chrysomelidae), which include some important pest species. For example, Sage & Tucker (1997, 1998a & 1998b) employed a beating method to knock leaf beetles, and other invertebrates, from stems and foliage onto a 2 m2 sheet laid out beneath the target willows. Invertebrates on the sheet were then collected with a pooter for immediate identification or temporary storage in a sample bottle. Sage & Tucker (1998a & 1998b) also conducted stem searches, to count colonies of aphids (Hemiptera: Aphidae) and some other invertebrate species that were likely to be missed, or under-represented, in samples collected by stem beating. Pitfall trapping has been extensively used for the study of ground beetles (Carabidae), rove beetles (Staphylinidae) and spiders in arable fields and many other habitats. Pitfall traps were used in SRC crops by Baxter (1996), Slater et al. (1997) and Coates & Say (1999). Earthworms were sampled by Coates & Say (1999) using an irritant chemical applied to the soil surface. The irritant caused worms to rise to the surface, where they were counted, washed and returned. Sage & Tucker (1998a) sampled earthworms and other, relatively large (>2 mm) soil-dwelling invertebrates, by collecting 25 soil samples, each approximately 15 x 15 x 12 cm deep (2.7 litre), from an SRC plantation and two nearby pastures. 33 4.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops Most of the standard invertebrate sampling methods described in 4.2 are likely to be feasible for use in SRC, although there may be some practical difficulties, that make sampling more time consuming (and more expensive) than in other habitat types. For example, methods used to sample invertebrates in SRC or Miscanthus crops should allow for the relative difficulty of movement (for recorders) and the difficulty of digging in dry soils with dense networks of roots or rhizomes. The nature of Miscanthus crops will make several standard methods impractical for use. Cumbersome equipment, such as a D-vac suction sampler, may not be a desirable option for use in such dense crops. In SRC, sampling of invertebrates on the stems and foliage of the crop is probably best achieved by stem beating and, if required, direct examination of leaf samples. Even these methods have some associated problems, however. For example, leaves cannot easily be collected from throughout the canopy when crops are taller than 2-2.5 m (although the flexibility of stems does allow some sampling at heights above normal reach) – so species predominant in the upper canopy may be under-represented or missed. In twin-row SRC plantations, collection sheets positioned on one or both sides of a double row will not collect all invertebrates dislodged when the plants are beaten – as many will fall directly downwards into the area between the crop rows. As the size and positioning of sheets, and the frequency and strength of stem beating, is standardised at all locations this may not be of great significance, although it is possible that some species, perhaps the heavier ones, may consequently be underrepresented. Invertebrates on the foliage of ground vegetation can be sampled by sweep-netting, if the vegetation is of an adequate height and ground cover is sufficient to justify sampling. In Miscanthus crops, beating is unlikely to be feasible, because of insufficient bare ground on which to position collection sheets. Sweep-netting and direct searches of leaf samples may be the only feasible options for foliar invertebrate sampling in Miscanthus. Beating, sweep-netting and D-vac sampling are all best performed when vegetation is dry, reducing suitable sampling opportunities. Digging soil pits, to extract large soil samples can be severely restricted by dry soils and dense networks of roots or rhizomes. Even the extraction of relatively large soil cores may be slightly difficult in established crops. These factors may restrict the sampling of earthworms, and slow the rate of sampling for other large soil invertebrates, such as cranefly larvae (Tipulidae) or beetle larvae (Coleoptera). Digging holes for insertion of pitfall traps may also be more difficult than in most habitats, but should still be readily achievable. In particularly difficult locations (e.g. long established willow or poplar crops with many large, woody roots near the soil surface), one option might be to use relatively small volume cups as pitfall traps. Traps are less likely to fill with water, the most frequent problem encountered when smaller volume cups are used in open habitats, because of the high degree of rainfall interception by the crop canopy. If traps are to be changed relatively infrequently (e.g. intervals of two weeks or more), trap flooding may still 34 be a problem. In these cases, plant pot saucers supported by wire (as described earlier) can be used to exclude rainwater. Note that restricted movement through SRC and Miscanthus will make the carrying of large trays of pitfall traps relatively difficult. Pitfall traps may be very hard to locate in dense Miscanthus crops, so careful and appropriate marking of trap locations will be essential. Water traps should be an appropriate method for sampling true flies (Diptera) and some other groups of flying insects in biomass crops. Theft and vandalism, which can be a problem for these highly visible traps (particularly when located in publicly accessible areas), are likely to occur less often within tall energy crops, where visibility is reduced. Sticky traps, another method of trapping flying insects, may be less suitable in these crops, due to the close proximity of vegetation to which traps may stick during movement on windier days. Direct searching of stems (as used by Sage & Tucker, 1998a, for counts of aphids and some other groups) and coppice stools may be a suitable technique for surveys of invertebrate species that are difficult to sample by other methods. Methodologies can readily be developed to provide quantifiable data suitable for statistical analysis. 35 5. BIRDS 5.1 Bird species diversity in biomass crops 5.1.1 Spring/summer The most common breeding birds in SRC are those species most commonly associated with scrub and hedgerows, although the predominant species will be heavily dependent upon rotation stage/crop height (Sage, 1998). Other species will predominantly utilise crop edges and the wide grass headlands around SRC crops. As has been previously demonstrated in traditional coppice stands, different bird species have strong preferences for different stages of growth (Fuller & Moreton, 1987; Fuller et al., 1989; Fuller, 1992; Fuller & Green, 1998). Fuller & Green (1998), reporting results of a 10-year study of breeding bird populations in a coppiced lime (Tilia cordata) plantation in Worcestershire, found that overall densities of birds were generally highest in recently coppiced plots. Warblers (Silviidae) were much more abundant in recent coppice, and almost absent from old coppice – with warbler populations collapsing after 11-12 years of re-growth. A four-year bird survey at a site in Northern Ireland (Sage & Tucker, 1998a) recorded a total of 32 species that used the SRC crop, and a further 12 species on farmland that apparently never used the SRC. Of 22 breeding species at the site, pheasant (Phasianus colchicus) and reed bunting (Emberiza schoeniclus) always incorporated SRC within their territories. Dunnock (Prunella modularis), sedge warbler (Acrocephalus schoenobaenus), garden warbler (Sylvia borin), blackbird (Turdus merula), song thrush (Turdus philomelos), bullfinch (Pyrrhula pyrrhula) and lapwing (Vanellus vanellus) all included SRC in almost all territories (85% or more). The four most common species at the site – willow warbler (Phylloscopus trochilus), wren (Troglodytes troglodytes), robin (Erithacus rubecula) and chaffinch (Fringilla coelebs) – all used SRC to a significant, though lesser, extent. However, three other regularly breeding species never included SRC in their territories: blackcap (Sylvia atricapilla), chiffchaff (Phylloscopus collybita) and goldcrest (Regulus regulus). Coates & Say (1999), in an intensive study of five SRC sites in southern England, recorded 39 breeding species (predominantly songbirds) whose territories included SRC. Twenty-seven of these species held territories contained within SRC and the other 12 had territories that extended into SRC plantations. An additional 23 bird species were recorded in SRC but did not hold territories that included SRC. As SRC plantations aged, the species composition changed and density of breeding birds increased. Coates & Say (1999) recorded six species of conservation concern (Red List species), most of which were strongly associated with a specific age class of coppice. The early stages were favoured by corn bunting (Emberiza calandra) (years 0-1) and skylark (Alauda arvensis) (years 0-2), linnets (Acanthis cannabina) were most abundant in year 2 and bullfinches in year 5. Song thrushes and reed buntings appeared to have less clear preferences (years 1-5). It should be noted most SRC crops would be harvested by year 3, and the absence of any harvest at most of Coates & Say’s sites during their study should be regarded as atypical. 36 Migrant insectivorous species, such as willow warbler, are particularly common in two and three-year-old willow SRC (Singleton & Bowes, 1991; Sage et al., 1994; Sage & Robertson, 1996). Poplar appears to support lower densities of songbirds, especially warblers and buntings (Sage et al., 1994; Sage & Robertson, 1996). Slater et al. (1997) recorded several warbler species within willow SRC plots in the SW Midlands and in Mid-Wales: willow warbler, sedge warbler and garden warbler at both sites, and chiffchaff at the site in Wales. They also recorded some evidence of whitethroat (Sylvia communis), dunnock and reed bunting breeding within SRC. Several other species were regularly observed around the plantation edges, including wren, robin and chaffinch. Christian et al. (1997) and Collins et al. (1999) surveyed bird populations in hybrid poplar plantations (2.7-4.0 ha) and surrounding land, in the USA. All poplars had been planted as experimental, biomass energy crops, at a spacing of 2.5 x 2.5 m wider than SRC crops in the UK. Surveys were conducted in the breeding season (June-July) and during the period of autumn migration (August-October). They found that avian abundance and species richness were consistently higher in poplar plantations than in surrounding arable fields. However, abundance and diversity were lower in poplar stands than in forests or non-wooded ‘wildlands’ (e.g. old or conservation scheme grassland). Poplars appeared to be more attractive to birds in agricultural landscapes than in forest landscapes. Similar results were reported by Schiller & Tolbert (1996). They also found that bird species in poplar biomass plantations in the USA, although lower in number than in natural forest, were a mixture of ‘openland’ and forest species. Little is currently known about the use of Miscanthus by breeding birds. However, the relative scarcity of invertebrates on the crop will mean that it is a less valuable habitat for foraging insectivorous birds. The similarity of the crop to reeds might, however, make it a suitable alternative nesting habitat for reed-bed species – if surrounding habitats provide sufficient food resources. Beyea et al. (1995) found that switchgrass crops, in Iowa (USA), provided significant habitat for several declining species of specialist prairie grassland birds. 5.1.2 Winter Bird surveys undertaken by Sage & Tucker (1998a) in the winter of 1996-97 (November to March), at seven willow and poplar SRC sites in southern England, recorded 29 species. The total number of species recorded at any one site, in five visits, ranged from 9 to 19. Those present at all sites were blackbird (Turdus merula), robin, wren, dunnock, blue tit (Parus caeruleus), chaffinch and pheasant. Pheasants were the most abundant birds, although there were release pens of pheasants and partridges in the vicinity of all sites and local distributions of these species were not considered to be representative of wild populations. Long-tailed tit (Aegithalos caudatus), the most abundant species after pheasant, and song thrush (Turdus philomelus) were both recorded at six sites. Although very few species were recorded in large groups, Sage & Tucker reported that flocks of larks and finches had been recorded in previous years. The mean density of over-wintering birds in SRC was 3.9 per ha. Bird densities were significantly lower in larger SRC 37 plantations, indicating the relative importance of plantation edges. The wide headlands of SRC crops were utilised by species such as yellowhammers (Emberiza citrinella) and finches. Skylarks and meadow pipits (Anthus pratensis) were most frequently observed in areas of recently harvested SRC. Coates & Say (1999), in a five-year study of sites in southern England, recorded 51 species in SRC. The overall density of over-wintering birds was high in the planting year (year 0), decreased over years 1-3, then increased again in years 4 and 5. At two sites where the crop was harvested four years after planting, bird densities fell in the following winter and then began to rise again. Numbers of buntings, finches, skylark and snipe (Gallinago gallinago) declined as the coppice aged, while numbers of pheasant, blackbird, long-tailed tit and blue tit increased. Sage & Tucker (1998a) recorded several species of conservation concern, including the Red List species reed bunting, song thrush, skylark and linnet. Coates & Say (1999), in their winter surveys, recorded 13 species of conservation concern in SRC, including grey partridge, snipe, woodlark, song thrush, linnet, bullfinch and reed bunting. Radio-tracking of snipe, at a site in Devon, has produced some evidence that SRC provides suitable day-time roosting sites for this species, which then feed by night in nearby pastures (Sage & Tucker, 1998a). 5.2 Standard bird survey methods The various techniques for surveying bird populations have been described by several authors, including Bibby et al. (1992), Buckland et al. (1993) and Gibbons et al. (1996). Gibbons et al. (1996) state that there are broadly two types of bird census – those for species that are evenly distributed across the landscape (i.e. territorial species) and those for species that are highly clumped during the breeding season (e.g. grey herons, rooks, black grouse, sea birds). In SRC and Miscanthus, those methods applicable to clumped species will rarely be useful (as bioenergy crops are unlikely to provide suitable habitat for these colonial breeders), so only the main methods applicable to surveys of evenly distributed species will be considered here. Territory mapping The aim of territory mapping is to estimate the boundaries of breeding bird territories and, thus, the numbers of breeding pairs of each species within the survey plot. Territory mapping techniques require fairly intensive fieldwork, at regular intervals throughout the breeding season. Gibbons et al. (1996) recommend that census plots, which should not be linear, need to be at least 15-20 ha in temperate woodland, or 60-80 ha in more open habitats, such as farmland, moorland or grassland. Although open habitats require larger census plots, as few as five visits per year may be adequate, compared with a minimum of ten required for areas of woodland with higher densities of breeding birds (Gibbons et al., 1996). 38 The British Trust for Ornithology (BTO) have operated a national census of breeding birds that has, until recently, been based on a territory mapping methodology known as the Common Birds Census (Marchant, 1983; Sykes & Lane, 1996). This methodology has also been widely used in other surveys. It requires ten census visits between mid-March and late June. Visits should be fairly evenly spaced throughout this period, ensuring that early and late breeding species are recorded. Eight visits are completed in the morning (starting before 09.00 and finishing before 12.00) and two in the evening. The positions of all birds observed or heard are recorded on a map, using species codes. Bird activities such as calling, singing and displaying are also recorded using a standardised notation. After all visits have been completed, all records for each individual species are combined on a single map (one per species) – from which the number and position of breeding territories can be estimated. Territory mapping is only really suitable for surveys of territorial species during the breeding season. However, the methodology used to produce maps of breeding territories does allow a straightforward calculation of bird densities and provides a good picture of bird distribution across a site at any time of year, which may be useful for the analysis of bird-habitat associations (Gibbons et al., 1996). Consequently, a simplified common bird census methodology might also be used for autumn and winter bird surveys. Modified territory mapping techniques have been used in many studies, in a range of habitats, including traditional coppice and woodland. For example, Fuller & Green (1998), in a study of breeding bird populations in coppiced lime stands, made three survey visits each year, in mid-May. Bellamy et al. (1996), in a survey of small woods, visited each site four times between mid-March and early August. Point counts This method involves bird observations from a number of fixed positions for a short, pre-determined period. Point counts are best suited to recording highly visible or vocal species (e.g. songbirds) in a wide variety of habitats (Gibbons et al., 1996). Point counts will provide estimates of the relative abundance, or absolute densities, of different species at any chosen time of year. Point-count stations are laid out systematically (according to a grid) or randomly. The sample may be stratified, if appropriate. Gibbons et al. (1996) recommend that there should be more than 20 stations at any site, and that these should be at least 200 m apart, to minimise the chances of recording the same birds at different points. They also suggest that the site should be visited at least twice and that the duration of counts at each station should be between three and ten minutes, with five minutes probably being adequate in most habitats. Counts should not begin immediately after the recorder’s arrival at the station, but a few minutes should be allowed for the birds to settle after the initial disturbance. Point counts can be made over an unlimited distance or within a pre-determined band. Donald et al. (1998), for example, recording breeding birds in coniferous and broadleaved woodland, counted only those birds observed within 50 m of their three point count stations. Each station was visited twice and each count continued for 10 minutes. 39 Such a methodology can provide relative indices of abundance, but a slightly more complex approach is necessary for estimates of density. Density estimates require birds to be counted in two or more distance bands. The simplest method is to record those birds in a band up to a fixed distance from the surveyor (e.g. 25 m in dense woodland and 50 m in more open habitats), and to record all those seen or heard beyond that distance separately (Gibbons et al., 1996). Standard formulae are then used to calculate the density of each species. Counts can be heavily influenced by time of day and weather conditions. Line transects This method involves recording birds along, or on either side of, a fixed transect (normally a straight line). Transects must be of a fixed length and randomly allocated. They must not be selected to follow footpaths, hedgerows, streams or other linear features – as this might heavily bias the results. Line transects are best suited to recording birds in extensive, open and fairly homogeneous habitats e.g. moorland (Gibbons et al., 1996). In the UK, the BTO have adopted a line transect methodology to replace the more labour-intensive territory mapping methodology used until recently. The Breeding Bird Survey (BTO, 1995; Sykes & Lane, 1996) requires surveyors to walk two straight line transects across a 1 km square. These transects are walked twice each year - ‘early’ and ‘late’ in the breeding season. Methods for estimating density are similar to those described for point counts. Catch per unit effort (mist netting) Catch per unit effort methods (mist netting) can be used, by qualified and licensed ringers only, to monitor changes in bird populations, productivity and survival (Gibbons et al., 1996). To allow such assessments, there must be standardisation of mist net locations, net size (height and length), net type, timing and duration of netting period and weather conditions during netting. This type of methodology – used in several established, long-term studies, including the BTO’s Constant Effort Sites (CES) Scheme (Peach et al., 1998) allows more than just the estimation of annual or longer-term changes in bird populations, but also gives an indication of the extent to which changes may be due to reduced/increased productivity or survival. Mist netting is usually considered to be most suitable for recording birds in woodland or scrub, although many of the CES Scheme sites are also in reed-beds. Birds that are caught in the mist nets are usually identified to species, aged and sexed before being ringed (if not already ringed). Mark-release-recapture (ringing) Mark and release methods for bird surveys, involves initial capture of birds by qualified and licensed ringers, and fitting of coloured leg rings (most widely used), wing tags, neck collars or radio transmitters. The use of highly visible, or otherwise readily detectable, rings or tags will usually make recapture unnecessary. 40 In practice, mark-release-recapture methods are infrequently used for population estimates in bird species, and are more commonly used for research on aspects of migration, survival/longevity, feeding patterns, habitat usage, etc. 5.3 Bird survey methods applied in studies of biomass crops Bird territory mapping, with repeated visits during the spring and summer, was used to survey breeding bird populations in SRC by Kavanagh (1990), Slater et al. (1997), Sage & Tucker (1998a) and by Coates & Say (1999). Similar methods, without the final analysis of territories, were used by Sage & Tucker (1998a) and Coates & Say (1999) to map the distribution of winter bird populations. Sage et al. (1994) and Sage & Robertson (1996) used point count surveys, recording all birds seen or heard within 50 m semi-circles. Mist netting was employed by Singleton & Bowes (1991) in their study of birds in an SRC plantation in North Yorkshire, trapping birds on 10 occasions between June and October. The study of US poplar biomass sites by Christian et al. (1997) and Collins et al. (1999) involved walking line transects through the centre of each poplar plantation (or other adjacent crops or semi-natural habitats) and around their perimeters. A novel method for the monitoring of pheasant and partridge movement into and out of SRC was developed by Baxter et al. (1996). A line of 0.25 m2 (0.5 x 0.5 m) quadrats filled with sand was laid along one edge of each SRC plantation. Regular inspections were made to count footprints of the two gamebird species being studied. 5.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops The use of skilled and suitably experienced ornithologists is essential for the accurate identification of birds in any field survey. Spring and summer surveys also require personnel capable of identifying bird calls and songs. Although species identification is much easier if birds are captured, for example by mist netting, such techniques can only be employed by suitably trained and licensed staff. Movement through SRC crops can be difficult, although pathways between pairs of tree rows can usually be fairly readily walked along at any time. Visibility through plantations is restricted at all times (other than shortly after planting, cut-back or harvest), but particularly so when tall crops are in leaf. This makes the need for highly competent ornithologists, with the skills to identify birds by sight or sound, even more critical. 41 Sand quadrats are potentially useful for surveying game bird usage of SRC, but regular inspections, and levelling of sand after rain, are essential. Despite the difficulties, territory mapping (or adaptations of territory mapping methodologies for winter counts) or point counts will be suitable in most surveys of birds in SRC. This will provide some compatibility with previous UK surveys. Bird surveys in established Miscanthus crops will be more difficult, because of the greater restrictions on movement and visibility. Territory mapping or point counts (at the edge of crops) should still provide useful data, but more intensive methods such as mist netting might be considered. 42 6. MAMMALS 6.1 Mammal species diversity in biomass crops Coates & Say (1999) in their study of five SRC sites in southern England, trapped four species of small mammal: common shrew (Sorex araneus), bank vole (Clethrionomys glareolus), wood mouse (Apodemus sylvaticus) and harvest mouse (Micromys minutus). However, only one site had all four species present – although the method used resulted in small sample sizes, which probably underrepresented the true diversity of small mammals present (see Sections 6.3 and 6.4). Slater et al. (1997) also trapped only low numbers of small mammals during five short trapping periods at a newly established willow SRC site in Mid-Wales. Three species were captured within the SRC: wood mouse (mainly), yellow-necked mouse (Apodemus flavicollis) and field vole (Microtus agrestis). Field voles, which were relatively abundant in adjacent rough pasture, were not captured in SRC until the final trapping period, in early October. Christian et al. (1997) and Collins et al. (1999) surveyed small mammal (Blarys, Clethrionomys, Microtus, Peromyscus, Sorex and Zapus spp.) populations in hybrid poplar plantations and surrounding land, in the USA. They found that small mammal abundance and diversity in poplar plantations were similar to those of adjacent or nearby arable crops. Small mammal diversity and abundance were, however, significantly higher in surrounding forests and scrub than in poplar plantations. There were no consistent differences between animals’ body mass or breeding activity in the habitats studied. Bodnor (1995; cited in Sage & Tucker, 1998a) found that populations of small mammals, such as the wood mouse, in SRC were affected by management intensity, with weedy SRC holding larger numbers than relatively weed free plantations. Sage & Tucker (1998a) recorded sightings, or other clear evidence, of at least nine species of mammal in SRC sites across Britain and Ireland, although they did not undertake any formal mammal survey. Among the most frequently observed were rabbit (Oryctolagus cuniculus), brown hare (Lepus capensis) and roe deer (Capreolus capreolus). The other species recorded were common shrew, wood mouse, bank vole, mole (Talpa europaea), red fox (Vulpes vulpes), badger (Meles meles) and stoat (Mustela erminea). Sage & Tucker (1998a) also suggested that additional species (e.g. hedgehog), not observed during their site visits, would be expected to utilise energy crops to some degree. Coates & Say (1999) recorded two species of bat in SRC – serotine (Vespertilio serotinus) and both the 45 kHz and 55 kHz sub-species of pipistrelle (Pipistrellus pipistrellus) – and hedgehogs, moles, rabbits, brown hares, brown rats, badgers and roe deer. Between three and 11 mammal species were recorded within the SRC at any single site. Rabbits were common at all five survey sites. Moles and brown hares were common at two sites. 43 Christian (1997) recorded tracks of deer and several ‘medium-sized’ mammal species in small hybrid poplar plantations (2.5 x 2.5 m spacing), in Minnesota, Wisconsin and South Dakota. From his results, he concluded that most mammal species normally associated with forests (e.g. squirrels, rabbits and hares) showed extremely limited use of the poplar plantations. Deer and carnivores (e.g. red foxes and coyotes) tended to travel through plantations, rather than make concentrated use of them. He suggested that the poplar plantations were functioning more as ‘openland’ habitats, rather than forest. 6.2 Standard mammal survey methods The relatively highly conspicuous, larger mammal species can be counted – although methods must take proper account of the likelihood of missing animals or double-counting. However, several mammal species that are of conservation concern are both secretive and occur at low densities. This makes them very difficult to observe and, therefore, to count. Methodologies for surveys of mammal species may, consequently, rely on counts of dung or footprints or the recording of evidence of feeding. Such ‘indirect’ methods usually provide indices of abundance, rather than measures of density (Sutherland, 1996b). Total (visual) counts Areas are divided into blocks and the number of individuals of the target species recorded in each. This method is particularly useful for large, conspicuous mammals in open areas. Movement of animals between blocks can result in double-counting and over-recording. Total counts can be used for deer or hare surveys. However, visibility restrictions in established SRC and Miscanthus crops are likely to make accurate counts difficult. Poor visibility is very likely to lead to underestimates of animal populations, as some animals present will not be seen. Counting breeding sites This method is useful for surveys of mammals that build obvious breeding/nesting sites, or those that live in underground lairs with relatively large and conspicuous entrance holes (Sutherland, 1996b). Counts of breeding sites are potentially useful for surveys of badgers (Meles meles), rabbits (Oryctolagus cuniculus), foxes (Vulpes vulpes) and squirrels (Sciurus vulgaris and Neosciurus carolinensis), but breeding sites may be misidentified (e.g. squirrel dreys mistaken for bird nests, or vice versa) and abandoned sites erroneously counted. Evidence of recent digging; fresh hairs, dung, bedding or tracks; and strong animal scents (usually readily detectable from fox earths and badger setts) all indicate that a breeding site is still in use. Recording and mapping of breeding sites over a period of several years can give a good indication of declining or expanding populations. If reliable estimates of the average number of individuals using each site can be determined, then counts of breeding sites can also be used for density estimates. 44 This type of survey is generally not invasive and is, therefore, not likely to require a licence from English Nature – as would be needed for research involving trapping badgers or disturbing their setts. Counting and mapping calls The standard method for assessing the relative abundance of bat species (Chiroptera) in different habitats/sites is to record their echolocation calls using a portable bat detector, which converts their ultrasonic sounds into a wavelength that is audible to the human ear (Sutherland, 1996b). One system commonly employed in the UK is to set the bat detector to a frequency of 45kHz, and to record the number and location of ‘bat passes’ using a map (Sutherland, 1996b; Sykes & Lane, 1996). One variation on this type of ‘fixed frequency’ recording is to locate two or more detectors at various locations, each pre-tuned to a different frequency (e.g. Grindal & Brigham, 1998). An alternative is to use a broad-band method, with an acoustic bat detector tuned to ‘frequency division’ – allowing the continuous recording of all frequencies (Vaughan et al., 1997). Different bat species can be identified fairly reliably from the wavelength of their ultrasonic calls. This can be determined by tuning the bat detector through a range of frequencies, to detect the wavelength of the strongest signal. The calls of different bat species also have other characteristic differences that can assist identification. Bat detectors can be directly connected to tape recorders, if required. Calls can then be subsequently identified, with the assistance of pre-recorded tapes or CDs (e.g. ‘The Bat Detective’). Sound analysis software (e.g. BatSound v3.31) is also available, for use with modern frequency division and time expansion detectors, to record and analyse calls and very accurately identify bat species. It is important to note that the use of these techniques for bat surveys does have certain limitations, for example: Detector surveys are biased to loud, abundant species such as pipistrelles (Pipistrellus pipistrellus). Quieter species, such as the brown long-eared bat (Plecotus auritus), will be more difficult to detect. Separation of the calls of many Myotis species (e.g. whiskered bat, Myotis mystacinus; Brandt’s bat, M. brandtii; Natterer’s bat, M. nattereri; and Daubenton’s bat, M. daubentonii) can be difficult or impossible using most tuneable bat detectors. Seasonality is very important. Surveys can only be conducted between late spring and early autumn. Ideally, several surveys should be completed between mid-June and early September. Timing, over the course of the night, is vital as bats are most active shortly after sunset and shortly before sunrise – although this varies between species. Weather conditions are also important. Surveys should not be carried out when rain is heavier than a light drizzle or when there are strong winds, because bats may not be flying in these conditions (Sykes & Lane, 1996). 45 More information on bat detectors can be found on various websites e.g. The Bat Conservation Trust (www.bats.org.uk/batinfo/batdets.htm), the University of Leeds (www.biology.leeds.ac.uk/staff/dawa/bats/Detector.htm), Stag Electronics Ltd. (www.batbox.com) and Alana Ecology Ltd. (www.alanaecology.com). Trapping Small terrestrial mammals, including mice (Rodentia: Muridae), voles (Rodentia: Microtidae) and shrews (Insectivora: Soricidae) are generally difficult to observe but can be quite readily trapped. Consequently, trapping is the preferred method for surveying most small mammal species. Traps are usually some form of metal box, with an entrance door at one end which closes when an animal either moves a lever or presses down on a treddle, whilst entering the trap. They are then unable to get out. Food is put in the trap, partly as a lure and partly as a source of food to ensure the survival of the trapped mammal. In the UK, the most frequently used trapping method for small mammals is the Longworth trap (Sutherland, 1996b; Fitzgibbon, 1997). These small, two-part aluminium traps are placed in pairs or groups of three, along transects or on a grid. Bedding material, usually hay, and food for both herbivorous and insectivorous mammals is placed in each. Normally, this would be cereal grain for mice and voles and insect pupae (fly castors from an angling shop) for shrews. Traps are checked twice a day (morning and late afternoon) over a period of 3-5 days. For example, traps may be set on a Monday afternoon, then checked twice a day up until, and including, Friday morning (i.e. over seven trapping periods – three days and four nights). Any eaten food, wet bedding, etc. is replaced. All trapped animals are identified to species, sexed, aged (adult or juvenile), weighed and given a unique mark (by clipping fur). Marking animals allows subsequent new captures to be distinguished from previously caught animals. This is then a mark-releaserecapture method that can provide an estimate of population size. Some animals tend to be ‘trap-happy’ and are caught repeatedly, whilst others tend to avoid traps. Weather conditions will have an influence on numbers of small mammals trapped, as they tend to be most active on dark, warm and dry nights (Sutherland, 1996b). In some studies, researchers have preferred to use ‘snap-traps’, which kill the small mammals that are attracted to them. These traps are simple mouse or rat traps, as commonly used to kill rodent pests in and around homes and offices. Snap-traps are very widely used in small mammal surveys in the USA, but live traps are preferred in Europe. Dung counts Location of the dung/faecal pellets of some mammals may be easier than observing the animals themselves. Dung counts, therefore, provide a useful technique for estimating the relative abundance of several species, including rabbits, deer, foxes and otters. It has been successfully used to assess differential use of a variety of habitat types within a species’ population range (Doney, 1998a). 46 Frequently used methods involve clearing all dung/droppings from transects of a pre-determined length and width, then to return and count all new dung deposited along those transects perhaps 14 days later (e.g. Sykes & Lane, 1996). Doney (1998a), using a computer model, evaluated four dung sampling methods for the evaluation of deer densities. He concluded that the methodology recommended by the UK Forestry Commission (eight 7 m x 7 m square plots laid out on alternate sides along alternate sides of a ground survey line) had the highest potential accuracy, and was not significantly slower than the other methods tested. Doney (1998b), however, has demonstrated that the rate of pellet decay (for fallow deer, Dama dama) is affected by factors such as air temperature, wind speed and (in some instances) crop/vegetation cover. Detailed information on deer survey techniques has been published by Mayle et al. (1999). The success of this method depends on reliable identification of dung deposited by different species. Useful information is provided by Bang & Dahlstrom (1974) and in other field guides. Feeding signs Some mammal species, particularly herbivores, leave very clear and recognisable signs of their feeding activity (Bang & Dahlstrom, 1974). For example, the presence of dormice in a woodland or hedgerow can be detected from characteristically holed hazelnut shells. Other methods Other methods for surveys of the distribution and abundance of mammal species include radio-tracking and thermal imaging (Gill et al., 1997). 6.3 Mammal survey methods applied in studies of biomass crops Small mammals Coates & Say (1999), in their intensive study of five SRC sites in southern England, included short periods of small mammal trapping, annually over a fiveyear period. They used plastic, ‘Longworth-type’ traps to capture mice, voles and shrews. Traps were set during May or June and checked every 2-3 hours, over a 24-hour period. Trapping, at all five sites, was initially undertaken in SRC plots, adjacent agricultural crops and adjacent non-agricultural habitats (e.g. hedgerows or scrub). Traps were positioned at 10 m intervals along transects running from near the edge of the coppice or agricultural field towards the centre. Traps were baited with cereal grain and either blowfly larvae or a mixture of commercial rodent feed and dog meat. Slater et al. (1997) set Longworth traps in willow SRC and surrounding rough pasture. Traps were set for two-night periods in February (pasture only), April, June, August and October. Relatively few mammals were caught. In one US study, Collins et al. (1999) trapped small mammals in hybrid poplar plantations, and surrounding habitats, using ‘snap-traps’. 47 Bats Coates & Say (1999) used a tuneable, heterodyne bat detector (Batbox III) at two SRC sites, walking the perimeter of the coppice and transects through it – between dusk and 1.00 am. Hedgerows and other nearby habitats were also walked. Other mammals Sage & Tucker (1998a) and Coates & Say (1999) made casual observations of mammals in SRC plots and recorded other evidence of the presence of mammal species. Christian (1997) recorded tracks of deer (Odocoileus virginianus), lagomorphs (rabbits and hares), carnivores (red foxes and coyotes, Canis latrans) and squirrels crossing 170 m long transects in hybrid poplar plantations and other nearby landuse types. Transects were walked 3-7 days after snowfall. 6.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops Longworth traps are generally accepted as the best method of assessing small mammal populations in a broad range of habitats, and are suitable for use in SRC, Miscanthus and other biomass crops. Staff should, however, be suitably trained and approved to operate these traps. The methodology used by Coates & Say (1999) would, however, need significant modification to enable a more complete picture of small mammal use of biomass crops to be obtained. Although sampling over a five-year period should allow for annual fluctuations in mammal populations, Coates & Say’s survey did not capture enough individuals to facilitate valid statistical analysis of their data. Sample size could readily be increased by extending the trapping period from one day to four or five, and by adding a second trapping period in the autumn (October). Previous studies have shown that small mammal populations in hedgerows and woodlands are much higher during autumn than in spring/summer, and this is also likely to be the case in biomass crops. Live trapping could also be used for some larger mammals, including Mustelids such as weasels, stoats and polecats. ‘Snap-traps’ that kill small mammals should not be used. Deliberate killing of shrews is illegal. Bat surveys should operate standard methodologies, using tuneable bat detectors. Transects should be walked along crop margins and, where possible, through the crop. Winter weather conditions in the UK would not permit the use of snow-tracking techniques, as used for mammal surveys in the USA by Christian (1997). Larger mammal species could be more efficiently surveyed using dung counts and, perhaps, counts of breeding sites. Total counts of deer or hares should also be feasible and might be considered, where sufficient numbers of staff are available to 48 ‘drive’ animals through the crop, with recorders positioned to count those that emerge onto the headland at the far side. Total counts obtained from driving mammals from crops will, however, be difficult in some situations e.g. where plantations are large, irregularly shaped and/or divided into compartments by hedgerows and ditches. More intensive autecological studies of larger mammals, perhaps to quantify their use of bioenergy crops relative to other habitat types, could be performed using radio-tracking techniques. 49 7. REPTILES AND AMPHIBIANS 7.1 Reptile and amphibian species diversity in biomass crops There have been no formal surveys of reptiles or amphibians in SRC, Miscanthus or other biomass crops. Sage & Tucker (1998a) did, however, report observations of common toads (Bufo bufo) and common frogs (Rana temporaria) in areas of damp grass in the headlands and rides of wetter SRC sites, and newts (Triturus sp.) at the edge of one willow plot. They also recorded one grass snake within an SRC crop in southern England. The relatively dry conditions found within most biomass crops are, however, likely to make them unsuitable habitats for amphibians and, similarly, the shady conditions will be generally unsuitable for most reptiles (Sage & Tucker, 1998a). It is possible, however, that some biomass crop sites (or at least the crop margins and headlands) might provide suitable habitat for slow worms (Anguis fragilis), which occurs on woodland edges, hedgerows and scrub (Arnold & Burton, 1978). Bioenergy crops might even provide potential habitat for smooth snakes (Coronella austriaca), although this species is currently restricted to southern counties of England, mainly in dry heathland (with mature heather, dwarf gorse and Molinia tussocks). 7.2 Standard reptile and amphibian survey methods Various methods are used for surveys of reptiles and amphibians. Commonly used methods for surveying amphibians include measurement of area/volumes of frog spawn, netting or bottle trapping of great-crested newts (Triturus cristatus). More intensive research projects may employ methods such as ring-fencing ponds, to direct breeding frogs or newts into large pitfall traps, where they can be regularly counted. Mainly nocturnal amphibian species can be searched for by torch or lamplight, preferably on nights when soil and vegetation is damp after a period of rainfall. Diurnal reptile species can be most readily observed on warm, sunny days – particularly in the mornings and late afternoons, when they are most active. At other times they may be found by overturning large rocks or logs. The relative abundance and distribution of snakes and lizards (including slow worms) can be assessed by the use of ‘tinning’/‘reptile mats’/refugia trapping. This involves placing squares (e.g. 75 x 75 cm) of corrugated metal sheeting, wood, plastic, carpet or other flat or corrugated material across the site, for reptiles to hide under. These ‘tins’ are best placed in sunny areas, most attractive to reptiles. Tins/refugia are then regularly checked and animals beneath may, if necessary, be captured by hand. Catching reptiles may, however, be difficult, potentially damaging (particularly to legged lizards) and must take account of any possible legal implications. Refugia traps provide useful comparative data on the relative usage of different sites or habitat types, but will not normally provide data to facilitate accurate estimates of population densities. 50 Further details on reptile trapping methods can be found in Foster & Gent (1996), Foster & Barr (1998) and Gent & Gibson (1998). Further information on amphibian surveys can be found in Foster & Barr (1998), Gent & Gibson (1998) and Biota (2003). Seasonality is particularly important in surveys of reptiles and amphibians. In Britain, all species hibernate throughout the winter months. Reptiles are most easily caught, and therefore best surveyed, between late April and late June or between late August and late September (HGBI, 1998). Amphibians breed communally, and are most readily observed in ponds during spring. April and May are usually the preferred months for surveys of breeding amphibians in breeding ponds (Biota, 2003). However, if frog spawn counts are to be undertaken, these should be done between late February and late April, with earlier starts in the south. Great-crested newts, for example, overwinter on land between October/November and February/March (HGBI, 1998). A proportion of the adults move to the breeding pond as temperatures begin to rise in February or March, with numbers peaking there around mid-April. At any one time, less than one third of newts might be expected to be in the water (HGBI, 1998). Newts also move between ponds and do not always stay in the water for the whole of the springtime breeding season. Young newts only occasionally enter the water and may occur up to 500 m from their pond (HGBI, 1998). Ring-fencing a pond between early February and mid-May, and placing pitfall traps in gaps, may result in almost 100% of adult great-crested newts entering the pond for breeding being caught. Alternatively, this method can be used to catch adults and juveniles leaving a pond between early June and late October (HGBI, 1998). Surveys for great-crested newts can only be undertaken by a suitably licensed worker. Licences are obtained from English Nature, Scottish Natural Heritage or the Countryside Council for Wales. Bioenergy crops, however, are not usually adjacent to ponds or other freshwater habitats. Confirmation of their use by dispersed or migrating amphibians will, therefore, require alternative methods. Direct searching is possible, beneath movable objects such as logs and rocks, but amphibians on dry land can be very difficult to locate – particularly during dry periods (HGBI, 1998). Best results are likely to be obtained through torch-light searches on wet nights. If a torch-light search shows that amphibians are present, then more quantitative data can be obtained by setting pitfall traps, with 5-10 m drift fences to direct animals into the traps (HGBI, 1998). 7.3 Reptile and amphibian survey methods applied in studies of biomass crops No evidence was found of any reptile or amphibian surveys in biomass crops, other than the observations noted in Section 7.1. 51 7.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops Most established amphibian survey methods are only appropriate for use in ponds or other freshwater habitats. Direct searches, either at night-time using torches or under rocks during the day, may provide evidence of reptiles and amphibians within and around biomass crops, but provide no comparable measure of abundance. Placement of refugia/tins for reptile species, may be appropriate – but may need to be situated in relatively open, sunny positions to maximise the probability of their use by the target species. The use of pitfall traps is possible, but drift fences may be very difficult to erect in dense crops. 52 8. RECOMMENDATIONS This comprehensive review of methodologies used in ecological monitoring in energy crops, and consideration of the applicability and practicality of using alternative ‘standard’ methods in SRC and Miscanthus, allows recommendations to be made for a basic framework of techniques for future ecological monitoring in energy crops. It is recommended that new UK ecological monitoring projects in energy crops should be encouraged to adopt a standard suite of protocols, although this should not preclude any originality or the inclusion of additional species or groups – where additional funding permits. Standard protocols and survey designs should follow 11 basic principles: 1. Surveys should, wherever possible, be designed to incorporate monitoring of a few ‘core groups’ which can be considered to be indicative of overall biodiversity in the plantation. These groups should include: ground flora species; ground beetles (Carabidae); some arboreal insects (e.g. leaf beetles, Chrysomelidae; and Lepidoptera larvae); breeding birds; small mammals (mice, voles and shrews). The list of core groups should be kept small, to allow for projects with limited funding; but a secondary list of ‘priority additional groups’ should be published – for measurement where resources allow. This secondary list should include representatives of the soil fauna, such as springtails (Collembola). It might also include butterflies (on and around crop margins), moths, bats and deer. 2. Surveys must not focus solely on groups for which SRC or energy grasses are known to provide valuable habitats. An ‘independent’ and wide-ranging approach is necessary to avoid any accusations of a bias in a survey’s conclusions. However, it is important to monitor the usage of energy crops by species of particular regional or national conservation concern e.g. Biodiversity Action Plan species, such as the brown hare (Lepus capensis) (UK Biodiversity Steering Group, 1995) and Red Data Book species (e.g. Palmer et al., 1997). 3. Methodologies should be based upon widely accepted techniques, which are appropriate for the target organisms in that particular study – preferably those which have been previously ‘tried and tested’ in surveys of energy crop plantations. For the groups mentioned in 1 above, plant frequency counts using nested quadrats, pitfall trapping, stem beating, bird censuses and live-trapping in Longworth box traps are considered to be suitable. 4. Methods used must fully consider the practicalities of sampling/recording within the energy crop concerned. For example, protocols must allow for the row spacing of SRC crops when specifying the location of quadrats for vegetation recording, or sampling positions for soil cores (e.g. if sampling for springtails or mites). Other important practical difficulties would include 53 severely restricted access to Miscanthus crops in summer; limited visibility within short rotation coppice (SRC) and Miscanthus during spring and summer and a dense mat of woody roots that inhibit digging (e.g. to extract earthworms). 5. Surveys should always be designed to facilitate valid and dependable statistical analyses of the data recorded. This will involve care in the selection of sample sites and levels of stratification, and consideration of the use of ‘controls’ - as well as robust field methodologies. Samples should be representative and take account of the important influences of factors such as climate, altitude, soil type, adjacent land-uses and plantation size on biodiversity within plantations. The factors considered in sampling design will, however, depend upon the specific questions being addressed – rather than simply being applied in accordance with any fixed suite of variables.. 6. New surveys should make full use of any opportunities for comparisons with ‘baseline data’ – either newly collected (i.e. from monitoring commencing prior to energy crop establishment) or already available (e.g. from research sites with biological databases dating from previous studies in the same fields). 7. Methodologies should, where applicable, be compatible with those used by national surveys - e.g. BTO breeding bird survey, Butterfly Monitoring Scheme or Rothamsted light survey (moths) – or national environmental monitoring networks - e.g. UK Environmental Change Network (Sykes & Lane, 1996). 8. Surveys should, wherever possible, allow direct comparisons between the biodiversity of energy crop plantations and other habitats within the local landscape – particularly the land-use that it has replaced (e.g. arable or grassland fields in agricultural landscapes). 9. Survey plots must incorporate field margins (i.e. crop edges and, the potentially important, grass headlands) and field boundaries (e.g. hedgerows). Grassy headlands might, in the longer-term, provide much of the site’s biodiversity, and one important positive impact of biomass crops may result from the removal of the negative effects of agrochemical inputs and livestock grazing from hedgerows and watercourses. 10. Surveys should also consider the wider, landscape-scale impacts of biomass crops on farmland ecology. Studies should take account of adjoining and nearby habitats, and consider linkages with semi-natural habitats, and potential species movements across the landscape. 11. One-off surveys have a value, but it is always desirable to repeat surveys over at least three years, to allow for temporal changes. Populations of many species change dramatically from year-to-year, as a result of climatic factors (e.g. summer rainfall, winter temperatures, and soil moisture), food availability, predator-prey interactions, etc. Repeat sampling will reduce the chances of missing a species, or underestimating its mean population size. The 54 precise number of surveys to make should, however, depend upon the objectives of the study. 9. ACKNOWLEDGEMENTS This review was funded by the UK Department for Environment, Food and Rural Affairs (Defra). Work was completed as part of the project Poplars: a multiple-use crop for European arable farmers (PAMUCEAF), which was funded by Defra (Project NF0408) and the European Commission (FAIR6 CT98-4193). Francis Kirkham, ADAS, provided helpful comments on the draft report. 55 10. REFERENCES Arnold, E N & Burton, J A (1978). 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