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ADAS WORKSHOP Techniques for Re-establishing Dwarf Shrub Heath University of York 30th March 2000 Contents 1. Introduction 3 2. Presentations 3 2.1 Heathland Restoration Following Bracken Control 3 2.2 Re-creating Dwarf Shrub Heath Vegetation 4 2.3 Reversion of Arable Land to Dwarf Shrub Heath 5 3. Planning and carrying out dwarf shrub heath restoration 6 3.1 Defining objectives 6 3.2 Preliminary site survey 6 3.3 Planning the restoration 7 3.4 Plot trials of restoration techniques 7 3.5 Monitoring restoration success 8 3.6 Longer term management 8 4. Restoration techniques - problems and solutions 8 4.1 Abiotic site characteristics 8 4.2 Biotic factors 9 5. Gaps in the knowledge 14 6. Conclusions 15 7. Acknowledgements 15 8. Contacts 15 2 1. Introduction The workshop was held as part of the Association of Applied Biologists (AAB) conference on ‘Vegetation management in changing landscapes’ at the University of York, March 2000. The workshop forms part of a MAFF-funded contract to aid the dissemination of information on upland research. The aim of the workshop was to outline techniques and discuss their application and merits. Three key projects involving the restoration and re-creation of dwarf shrub heath were selected. These projects illustrated a number of approaches to heathland restoration, the problems encountered and the techniques used to address them. The projects presented were: Heathland restoration following bracken control - Mike Le Duc, University of Liverpool Re-creating dwarf shrub heath vegetation - David Collins, ADAS Preston Reversion of arable land to dwarf shrub heath - Anne Bhogal, ADAS Gleadethorpe Following the presentations, discussion groups of between 10-14 people were led by each of the three speakers and used to identify: common themes between different heathland re-establishment programmes the process of planning and carrying out restoration techniques used the appropriateness of techniques to different situations the problems encountered, and potential solutions gaps in the knowledge, with suggestions of how to address these. This report outlines the three presentations given, summarises the findings of the workshop discussion groups and subsequent conclusions. 2. Presentations 2.1 Heathland Restoration Following Bracken Control Mike Le Duc, Applied Vegetation Dynamics Laboratory, University of Liverpool Bracken is a common invasive species within heathland habitats, and requires some control. Consequently bracken control by various means is frequently carried out, including techniques such as cutting, crushing, burning and spraying with herbicide. Although attempts to control or eradicate the species may have only limited success. A series of heathland sites across England and Wales were selected to represent different stages of bracken invasion. The sites were sprayed and the vegetation that developed was monitored at different times after spraying. Analysis showed that there was a difference in species composition in relation to time after spraying, but there was also a great deal of regional variation due to other site factors, particularly altitude. 3 Further analysis showed that the heathland vegetation that establishes after bracken control appears to begin to show signs of degradation within a few years. This may be related to succession. Heathland is one stage within a natural succession process, and requires active management to prevent succession continuing toward scrub or woodland. Methods to control invasive bracken within heathland systems may promote these succession processes, so vegetation developing on heathland areas after bracken control appear to move toward scrub vegetation types more quickly. Management after bracken control on heathland areas needs to address this potential problem, and revert the succession back toward heathland vegetation. In a second experiment a combination of several different bracken control treatments were applied to trial plots. Primary treatments were cutting (June), cutting twice (June/Sept.), cutting (June) with herbicide application (Sept.), and herbicide application (Sept.). Secondary treatments were fencing or no fencing. Tertiary treatments were the addition of Calluna brash, Calluna litter or no Calluna seed application. Secondary treatments of fencing did not affect the restoration of heathland vegetation after bracken control. The treatment of cutting and spraying was effective at reducing bracken, with heathland species establishing, but there was some invasion of other weed species that competed with the heathland species. Cutting twice a year, and adding Calluna brash reduced the ingress of weed species. In the short term the treatments appeared to be effective in controlling bracken and re-establishing dwarf shrub heath, but after some years Calluna died back. This highlights the need for continual management after the initial establishment of heathland species, and emphasises the role of succession within heathland restoration. 2.2 Re-creating Dwarf Shrub Heath Vegetation David Collins, ADAS Preston Re-establishment of dwarf shrub heath on former open-cast coal sites presents significant problems, and many of these problems can be site specific. To address these problems small scale plot trials are tested prior to any field scale restoration plans being developed. This directs restoration toward the potentially most successful and most cost effective restoration programme. Prior to open cast mining the land may have been under high grazing pressure, with dwarf shrub heath plants being suppressed, resulting in limited flowering and seed production. The seed bank is, therefore, likely to be very poor, containing seed that is perhaps 20 or more years old, and the quantity of viable seed will be low. The process of open cast mining requires the removal and storage the top soil and the peat substrate. Storage over a long period reduces the viability of seed in the seed bank, and removal/storage mixes the peat profile, diluting the viable seed in the upper layers by mixing these layers throughout the peat. All these factors result in natural regeneration from a seed bank being highly unlikely once the peat substrate is replaced. To overcome this propagules need to be introduced for restoration. Stored peat soils can become depleted in nutrients, particularly nitrogen that converts to ammonium under anaerobic conditions during storage, and is leached from the peat 4 once it is replaced on site. Therefore, nutrients can limit vegetation re-establishment, and careful application of fertiliser can be help to over come this problem. Again, plot trials are essential in establishing soil nutrient status. Soil pH may also need to be addressed, if land has previously been under agriculture for many years the repeated addition of lime may have raised the pH. Elemental sulphur can be added to reduce pH. Calluna seedlings require a particular microclimate in which to germinate and establish. They can be particularly susceptible to drought during their first few years. Nurse crops can be effective in encouraging Calluna establishment. Grasses are often used, with tuft grasses rather than creeping species being preferred. Seed for these can be gathered locally using a seed gatherer, and nurse crops may need to be sown at high density in order to increase establishment rates. Surface scarification can also increase moisture retention and encourage seedling establishment. As natural regeneration is unlikely, seed must be added to the area to restore vegetation cover. The innoculum can include heather brash (the top 10cm of the heather plant), heather seed capsules cut by a capsule stripper, or by cutting mature heather to collect seeds. Collection of heather seed needs to be correctly timed to ensure seed is ripe, in January or February. Using heather brash is bulky with a low seed to bulk ratio, which can facilitate spreading. Heather seed capsules give a higher seed content. The seed can be spread directly using intact seed capsules, or the seed can be cleaned and/or treated. Cutting older heather requires the material to be collected up using a hoover, which will also collect seed of other heathland species. Heather seed can be spread using a conventional muck spreader or lime spreader (which will require finer material) and spread at around 3 to 4 g/ha. The timing of the restoration steps can be critical. If the peat substrate is replaced but not immediately re-vegetated the bare peat can begin to erode as the replaced peat has lost its structure and is vulnerable to the abiotic environment. Undesirable species may also quickly invade. Clover can readily establish on nutrient-poor bare substrates, and out-compete heathland seedlings. The leafy clover plants also harbour herbivores, such as slugs, that will attack emerging seedling of more desirable species. If grass nurse crops are sown before heathland species the grasses can become establish and actually compete with the heathland species they are there to support. Long term management is also a consideration. Introducing management such as grazing, at the right time can be crucial to long term success of the heathland vegetation. 2.3 Reversion of Arable Land to Dwarf Shrub Heath 1 Anne Bhogal, 1Brian Chambers & 2Richard Pywell, 1ADAS Gleadethorpe; 2ITE Monks Wood In order to successfully re-create heathland on farmland it is important to understand the constraints imposed by past agricultural inputs and management. Arable soils typically have a higher soil nutrient status and pH than heathland soils, due to the application of inorganic fertilisers, organic manures and lime. Soil pH can be reduced using elemental sulphur (as powder). Fertility can be reduced using continuous cropping, deep ploughing to bury the nutrient rich top soil, and stripping off top soil. Long-term agricultural management reduces heathland seedbanks, and residual 5 fertility on ex-arable land can favour competitive non-heathland species. Natural regeneration of heathland on ex-arable land is unlikely and there is a need a need to introduce heathland species propagules. An on-going MAFF-funded project in the Brecklands ESA evaluates a number of techniques to revert arable land to heathland. Treatments included +/- nurse crop, +/sulphur, top soil removal, natural regeneration, and broadcast of Calluna seeds/litter. Sulphur application was effective at reducing soil pH to extremely low levels, but over three years pH levels increased and long term effects may not be sustainable. Acidifying soils usually results in a decrease of available P, K, and Mg. In these trials P tended to increase as pH decreased, showing the opposite trend. Removing top soil had no effect on pH, a limited effect on reducing available P, K and Mg, and was successful at reducing available N. Assessing the different allocation of N between NH4, NO3 and plant N showed that increased sulphur application increased the proportion on NH4-N. Heather established on acidified plots only, but there was a slow establishment rate with much bare soil for the first few years. Few other species competed/invaded into the bare soil areas - possibly because pH was too low. Long term competition from invading species may become a problem with slow heather establishment, and pH levels becoming less acidic over time. Future work is concentrating on management to control competition from non-sown species. 3. Planning and carrying out dwarf shrub heath restoration 3.1 Defining objectives Developing clear and precise objectives is seen as fundamental to planning restoration projects. The objectives of dwarf shrub heath restoration can be very different depending on the site, but three main themes can be identified; (1) where restoration begins with a highly disturbed site with little or no vegetation (e.g. after open cast mining or industrial peat extraction), (2) restoring heath from another land use type (e.g. reversion of arable land or afforested areas), (3) restoring degraded heathland vegetation with remnant vegetation (e.g. controlling invasive species such as bracken or competitive grasses, reducing grazing). Possible objectives identified for heathland restoration are: re-instating areas with semi-natural vegetation after industrial use providing or increasing amenity use providing or increasing wildlife value meeting nature conservation objectives for heathland habitats and species protecting habitats and species 3.2 Preliminary site survey Although three main themes of heath restoration were identified, it is acknowledged that restoration is usually very site specific, with each site showing a unique 6 combination of biotic and abiotic constraints. Once the main restoration objectives have been identified, a thorough site survey is essential. Final objectives may need to be re-assessed in the light of survey findings, and flexibility is often key to successful restoration. Site surveys should address some key areas. These include abiotic factors such as soil characteristics, hydrological conditions, altitude, topography; and biotic factors such as the viable seed bank, local seed source and the presence of invasive species. The main biotic and abiotic factors to consider including in a survey are presented in Table 1. Table 1. The main abiotic and biotic factors to consider in a preliminary site survey prior to planning a restoration project. Abiotic Factors Biotic Factors altitude seed bank viability climate/exposure local seed sources topography local vegetation types substrate type invasive, undesirable species pH competitive species nutrients/fertility associated fauna soil compaction/erosion long term management moisture/drainage herbivory contaminants/heavy metals 3.3 Planning the restoration Once the survey has identified the site’s characteristics and constraints, the results can be divided into characteristics that (1) cannot be altered and must be worked with, (2) need no amelioration, and (3) require some action to enable heathland restoration. Those characteristics that require action should be prioritised according to the objectives for the site, and then a programme of techniques assigned to address them. A step-wise plan of the restoration project should be developed, with an indication of time-scales. 3.4 Plot trials of restoration techniques The success of different techniques can be highly variable, and if time and resources allow, techniques should be trialed on a small area of the site. This is particularly important for large scale restoration projects where time, effort and money may be wasted by starting with inappropriate techniques. Some techniques that are successful on a small plot may still encounter problems when scaled up, and monitoring should highlight if this does occur. 7 3.5 Monitoring restoration success A comprehensive monitoring strategy should be planned and put in place to assess the success of the restoration project. Measures of success should be clearly identified early on in the project and be related to the initial objectives of the restoration. For example, if the restoration objective is to establish a range of heathland vegetation types, then the establishment and cover of key heathland plant species can be targeted. Alternatively, if the objective is to control an invasive species, then this species should be targeted for monitoring to assess its decline in cover and density. It is usually advisable to routinely monitor abiotic characteristics that have required some amelioration, such as soil pH and water tables, to ensure they are still at the appropriate levels. The monitoring should also be able to quickly highlight any problems that develop, so counter measures can be taken to address these. Targeting what to monitor and where to monitor can be very site specific, but concentrating effort on the more vulnerable areas most likely to show change, and any areas that are likely to be of high nature conservation interest, can be more cost effective. Monitoring methods also need to be robust, easily carried out and readily interpreted. 3.6 Longer term management Initial site restoration and the establishment of heathland vegetation can be challenging, and the need to restore sustainable heathland habitats may be overlooked in the process. Restoring a heathland system that requires continual high maintenance is costly in the long term, and less likely to succeed. Some management will always be required over the long term to prevent vegetation being invaded by shrub and tree species or to keep heather at different age stages, even if all other aspects of the restoration are successful. Long term management should be explored in the initial stages of the project development, including issues such as introducing grazing, rotational heather burning or cutting, and the long term control of invasive species such as bracken or soft rush. 4. Restoration techniques - problems and solutions Once it is decided to restore an area to dwarf shrub heath there are some site characteristics that may need to be addressed, and problems that may need to be solved. These problems can be divided into abiotic and biotic characteristics, and are discussed in turn. Some of these site characteristics and techniques to address the problems are presented in Table 2. 4.1 Abiotic site characteristics High pH values (more alkaline soils) can restrict dwarf shrub heath re-establishment. This may be a particular problem where the area has been under another land use for many years, particularly agricultural land use (or set aside) where lime may have been regularly added in the past. Soil pH can be reduced by adding elemental sulphur in either powdered or pelleted form. Pelleted form is easier to apply, but both forms are costly. Pulverised pyritic waste material may be a potential cheaper source of acidification material. There may be potential for other acidic waste materials, such as a mulch of bracken litter, to reduce pH, but little is known about the effectiveness 8 of these techniques. High nutrients can also restrict heath establishment and increase the competitiveness of undesirable species, particularly some grasses. Again, this is an issue on former arable areas, but high N-deposition on degraded heathland can also present problems. On areas with no remnant heathland vegetation top soil stripping can effectively remove nutrients, particularly nitrogen, but disposal of the stripped soil can be a problem. Deep ploughing the nutrient-rich top soil has limited effect as eventually the nutrients are brought to the surface, or plant roots (particularly of the vigorous competitive species) reach them. Ploughing may also bring up sub-surface soils that are higher in nutrients than the surface soils, and disturb soil structure leaving it more vulnerable to erosion. Removing nutrients using a temporary crop of high nutrient-demanding plant can be effective, as long as the plant is cropped and removed to take nutrients off the site. The crop plant should be carefully selected to ensure it doesn’t become an invasive species, and cropped before it sets seed. The rate of growth of the crop plant can be an issue. Where time is limiting fast growing herbs are more useful, perhaps using several sowings. Slower growing woody species could be considered in some long term restoration programmes. One potential problem may be that if scrub and trees were established to remove nutrients, when they come to be harvested there may be public concern about felling trees, as this vegetation could be viewed as the desirable restoration end point. Conversely, low nutrients can be an issue on severely disturbed sites. If soils are removed, stored and replaced for restoration, they can lose nutrients during storage. Nitrate converts to ammonium under anaerobic storage conditions, to be readily leached from the soils once they are replaced on site. Some limited addition of fertilisers can promote seedling establishment, but should not be continued over a prolonged period or more competitive species may begin to dominate at the expense of dwarf shrub heath species. Site hydrology may require management, although this will depend on the type of heath vegetation that is being restored. On areas where extensive drainage has occurred, these drains may need to be blocked to raise the water table. If dry conditions are the result of a freely draining substrate, mulches or other inert material can improve moisture retention. Introducing some organic matter into the soil can improve moisture retaining properties, but may also increase nutrient availability and therefore may not be acceptable. Where flooding is a problem improving drainage by careful installation of drains can be helpful, although the possibility of encouraging erosion may make drainage less desirable. Maintaining drains may also be costly, and thought needs to include where the extra water will be drained to, to prevent causing problems elsewhere. 4.2 Biotic factors Areas that have been under a different land use for some time, that were previously heavily grazed with limited flowering/seed production, or have been highly disturbed, are likely to have a depleted viable seed bank. Areas may also suffer from a lack of local heathland vegetation from which seed rain can arrive. Natural revegetation is, therefore, highly unlikely. To overcome this, seed will need to be brought into the 9 area either in the form of heather brash, heather litter, heather seed capsules or cleaned seed. As dwarf shrub heath restoration requires a mix of heathland species, rather than heather alone, collecting litter from established heathland areas will introduce a variety of species. Cleaned seed from typical heathland species can also be sown. Collecting seed or brash/litter should be done sensitively so as not to damage the ‘donor’ heathland site. Alternatively, use can be made of cut material taken from fire breaks or from general management on other sites. Local seed sources are considered best, as they are likely to have species that will grow best for that region. Importing propagules can also import undesirable species such as ticks, heather beetle or invasive plants, and care should be taken to avoid collection of propagules from areas known to have these problem species. If seedlings do not appear to establish well on bare ground there may be several possible causes. One is that conditions such as pH, nutrients or moisture are not correct and these should be monitored regularly. Many dwarf shrub species, including heather, require associated mycorrhiza to establish well. Introducing propagules using cleaned seed may reduce mycorrhizal associations, particularly if there are no remnant heathland species at the site from which mycorrhizal associations could develop. Introducing seed via brash and litter may counteract this, but there is little information on this aspect of heathland restoration. Seedlings of all species can be susceptible to drought in the early stages of establishment. This may be due to a poorly developed root system encouraged by an over-supply of nutrients, or due to environmental conditions. Several remedial actions are available. A vegetated surface can be scarified before seed is broadcast to create depressions that retain water better. On bare areas a nurse crop can be sown alongside the heathland species. The species of nurse crop should be carefully selected so as not to invade or compete with the heathland species, and native heathland grass species are preferable as they are likely to form a permanent part of the sward. Possible nurse crops are chewings fescue (Festuca rubra subsp. commutata), sheep’s fescue (Festuca ovina agg.) and wavy-hair grass (Deschampsia flexuosa). Nurse crops should be sown at the same time as heathland species or they may gain a competitive advantage and limit other vegetation establishment. A mulch can also act to retain moisture, and should also be poor in nutrients and sterile so as not to introduce unwanted plant species. A nurse crop, mulch or scarification may also help protect against frost damage on young seedlings. Competition between dwarf shrub heath species and introduced species (either invasive plants or nurse crops that become too vigorous) can be a problem in establishing vegetation on site. In addition, some desirable heathland species may become invasive and competitive if conditions favour their establishment at the expense of desirable species. Invasion by soft rush (Juncus effusus) can be a problem on some wetter sites, particularly if there is ground disturbance. If soft rush is likely to be a problem, which can be determined either by looking at local vegetation or by germinating peat cores in the greenhouse to assess the viable seed bank, then reestablishing a vegetation cover quickly is important. This can be done by sowing seed immediately, or by keeping turfs of the stripped vegetation and replacing them once the site is restored. Seed bank studies are also a good way to assess for any other potentially problematic species. The invasion of undesirable species such as bracken or clover, may can be contained by herbicide spraying. For well established competitors within a degraded heathland system, such as grasses or bracken, spraying 10 may need to be repeated to retain control. The long term sustainability of repeated herbicide application, and long term effects on the heathland system are not well researched. 11 Table 2. Issues arising from dwarf shrub heath restoration, and the possible management options available. Issue Management Option Other Considerations high pH addition of pelleted/powder elemental sulphur addition of crushed pyritic waste costly, hazardous to apply potential success unknown high nutrients remove top soil deplete by continuous cropping deep ploughing damaging, disposal of top soil costly requires careful selection of crop species, slow to have an effect damaging, nutrients can resurface low nutrients add fertilizer requires careful application to ensure correct amounts are added too dry block drains/outflow reduce water inputs downstream improve soil texture/moisture retention with a mulch guard against introducing nutrients or undesirable species or organic matter too wet improve drainage guard against erosion erosion improve soil stability by re-contouring Impossible on highly disturbed sites no viable seed bank or introduce propagules using heather seed, brash or local seed rain seed capsules Guard against introducing unwanted species such as ticks, invasive plants seedlings fail to establish on bare ground Select species carefully, and sow with the heathland species Ensure it is weed free and low in nutrients use untreated seed or brash use local seed sources, or seed for similar climate/environmental conditions use nurse crop species use a mulch micorrhizal inoculation wrong provenance 12 Issue Management Option pH/nutrients seedlings fail to establish on vegetated ground competition from non-sown species scarify surface to improve microclimate seed at higher density use a mulch micorrhizal inoculation wrong provenance Other Considerations check these are still appropriate pH/nutrients ensure it is weed free and low in nutrients use untreated seed or brash use local seed sources, or seed for similar climate/environmental conditions check these are still appropriate pH/nutrients spot herbicide application cutting/crushing check these are still appropriate can harm desirable plants may need to be repeated 13 5. Gaps in the knowledge During the workshop discussions several areas were identified where information was lacking, or difficult to access. For each point raised there was also a discussion on how to remedy the problem, and a possible suggestion on how to take this forward. These are presented below. There is a need for a more integrated approach to habitat restoration as a whole, enabling the most appropriate habitat to be restored to a site on the basis of site limitations, regional/local variation, historical land use. This would require better communication between the various organisations involved in habitat restoration projects, co-ordinated by an overseeing body. Guidelines and information on the practical management options, techniques to overcome specific problems, where to obtain materials, etc. are needed. The publication of information leaflets would be useful. There is a need to increase our knowledge of the processes important in heathland systems to be able to better predict the outcome of restoration, and reduce the time/effort/expense involved. Processes to focus on might be nutrient cycling, the role of mycorrhiza, competitive interactions between plant species, and successional processes. Research programmes could address these. Further monitoring of the long term effects of some potentially more harmful management techniques, such as repeated herbicide application, on the restored heathland system and adjacent habitats is needed. Research could address this issue. Monitoring of the long term effects of removing heather seed/brash from the ‘donor’ heathland sites should be carried out. Possible areas for concern could be effects on the vegetation structure, competitive interactions and biodiversity. This could be incorporated into the ‘donor’ site’s management plan. Guidance is needed on when to best introduce additional management after heathland species are established to prevent site degradation after restoration, e.g. introducing grazing, shepherding, repeat herbicide spraying. This may require additional research, and adequate dissemination of results in the form of leaflets or guidance notes. There is a significant need for greater integration of the initial restoration programme into a long term management plan for each site - we need to know more about the long term sustainability of the systems we restore, and their benefit to biodiversity. This could be addressed through carefully planned, long term monitoring of restored sites. The current wealth of expertise and knowledge is not always readily available, or easy to access. There is an immediate need for greater access to information perhaps by setting up a body who are proactive in gathering information on heathland restoration projects, and making it available through newsletters/internet/advice line/email/working group. 14 6. Conclusions From the workshop discussions a common point is the need for clear objectives to the restoration programme before starting. This includes the need to keep within the limitations imposed by the site that cannot be altered, or are perhaps too costly to be tackled. In addition there is a need to be sympathetic to the regional and local situation, and to put the restoration in a wider context to ensure limited resources are best allocated. There is also a need for clearer guidance on what techniques were suitable to different situations, and how to monitor restoration success effectively, particularly in the longer term. One important point raised is the wealth of knowledge and expertise that is potentially available, but often difficult to access. There is a feeling that similar problems are being encountered in many restoration projects, and a forum to share gained experience and learn from this would be beneficial, could reduce time, effort and associated restoration costs while increasing success. It is also highlighted that some areas need more research, including long term strategies for bracken/rush control, integrating restoration with grazing management, and restoring sustainable heathland systems that contribute to landscape, amenity and wildlife value. 7. Acknowledgements The organisers would like to extend a warm thanks to the three speakers and workshop participants. Thanks also to the Association of Applied Biologists for enabling us to hold the workshop in association with their conference, and particularly to Carol Millman (AAB Conference Manager) for all her help. Many thanks to Sarah Gardner for comments on the report. The workshop was held as part of a MAFFfunded contract on ‘communication of work on moorland management to land managers, policy advisors and the research community’ (Project BD1217). 8. Contacts For further information, please contact: Sarah Ross, ADAS Redesdale, Rochester, Otterburn, Newcastle-upon-Tyne, NE15 1SB, tel: (01823) 520 608; fax. (01830) 510 451; email [email protected] Sarah Hetherington, ADAS Pwllpeiran, Cwmystwyth, Aberystwyth, Dyfed, SY23 4AB; tel: (01974) 282229; fax: (01974) 282302; email: [email protected] 15