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© Ian D. Rotherham 2015
HABITAT MANAGEMENT CONCEPTS: ECOLOGICAL &
ENVIRONMENTAL CONTEXT: BIOGEOGRAPY, BIOMES,
KEY ENVIRONMENTAL FACTORS & LIMITING FACTORS
An Introduction to the British Environment and Biogeography in relation
to site management issues & context
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Warren, A. & French, J. R. (eds) (2001) Habitat Conservation: Managing the Physical Environment.
Wiley, London.
Sutherland, W.J. (ed. (2000) The Conservation Handbook. Blackwell Science, London.
Rotherham, I.D. (2013) Eco-history: An Introduction to Biodiversity and Conservation. The White
Horse Press, Cambridge.
Rotherham, I.D. (2008) Lessons from the past – a case study of how upland land-use has influenced the
environmental resource. Aspects of Applied Biology, 85, Shaping a vision for the uplands, 85-91.
Alexander, M. (2008) Management Planning for Nature Conservation: A Theoretical Basis and
Practical Guide. Springer, Netherlands.
Rotherham, I.D. (ed.) (2013) Cultural Severance and the Environment: The Ending of Traditional and
Customary Practice on Commons and Landscapes Managed in Common. Springer, Dordrecht.
Rotherham, I.D. (ed.) (2013) Trees, Forested Landscapes and Grazing Animals: A European
Perspective on Woodlands and Grazed Treescapes. EARTHSCAN, London. 412pp
Rotherham, I.D, Agnoletti, M., & Handley, C. (2014) The End of Tradition? Aspects of Commons and
Cultural Severance in the Landscape. Part 1 & 2, Wildtrack Publishing, Sheffield, 427 pp.
Wheater, C.P., Bell, J.R. & Cook, P.A. (2011) Practical Field Ecology: A Project Guide. John Wiley &
Sons Ltd, London.
Emery, M. (1989) Creating Urban Habitats: Promoting Nature in Cities and Towns. Croom Helm,
London.
THE ENVIRONMENT
1. The physical, chemical and biological conditions surrounding an organism.
2. Factors that have an effect on the life of an organism during some stage of its
development are called environmental factors.
3. The plants and animals forming the biotic part of an ecosystem will be those that can
tolerate the prevailing environmental conditions.
4. No organism exists in isolation. Each must be considered in the context of its
environment as this determines the conditions for life.
© Ian D. Rotherham 2015
TYPES OF ENVIRONMENTAL FACTORS
Environmental factors can be placed in 4 groups:
a) Climatic Factors: Including light, temperature, water availability, wind.
b) Edaphic Factors: Soil characteristics such as nutrients, acidity, moisture content.
c) Topographic Factors: Including terrain factors such as slope angle, slope aspect,
altitude.
d) Biotic Factors: Interactions of living organisms such as competition, grazing,
shading, predation, parasitism, disease.
When studying ecosystems, it is obvious that these four groups of environmental factors are
interrelated. It is therefore very difficult to isolate the influence of individual environmental
factors.
e.g. Topography and climate influence soil development; climate and soil influence the
pattern of biotic factors by determining which species can inhabit an area.
Environmental factors include both Biotic (or Biological) and Abiotic (or Physical)
However, the fundamental characteristics of any ecosystem will be governed by its abiotic or
physical components. The effects of these factors may be modified by the plants and animals
of the system, for example, trees creating shelter from strong wind. The extent of this
modification is limited.
All these environmental factors vary through time and space. Living organisms exhibit
definite responses to this variation, producing distinct relationships between the
environmental factors and the specific communities within an ecosystem. These relationships
are often very intricate, with complex interactions between the organisms and their
environments, and amongst the organisms themselves.
Historic factors (especially history of use, exploitation, and management) may also be very
important. These may be recent or long-term.
Try to recognise and identify key factors or influences. In particular, look for Limiting
Factors, Trends and Directions.
© Ian D. Rotherham 2015
MAIN ENVIRONMENTAL FACTORS:
1) BIOLOGICAL
(See later notes on competition, predation etc)
2) PHYSICAL
KEY PHYSICAL ENVIRONMENTAL FACTORS
a.
GEOLOGY (solid / drift) & TOPOGRAPHY (landform)
b.
LOCATION & CLIMATE
c.
LOCAL FACTORS (Micro-climate, altitude, aspect, slope drainage regime, landuse etc)
These influence key characteristics of the ecosystems particularly energy flow and available
nutrients, and seasonality.
These combine as below:
GEOLOGY
TOPOGRAPHY / CLIMATE
(In the Sheffield area)
BUNTER SANDSTONE
ALTITUDE
*COAL MEASURES
(*Includes Sandstone, Shale, +/- Coal)
MILLSTONE GRIT
ASPECT
SLOPE
MAGNESIAN LIMESTONE
DRAINAGE REGIME
CARBONIFEROUS LIMESTONE
RAINFALL
(& LOESS, BOULDER CLAY)
VOLCANICS etc)
TEMPERATURE REGIME
© Ian D. Rotherham 2015
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Influence
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SOIL, NUTRIENTS, MOISTURE
SOIL MOISTURE, SOIL DEPTH,
DECOMPOSITION RATES,
TEMPERATURE
FAUNA, FLORA
NUTRIENTS, TC, RAINFALL
STABILITY, EXPOSURE
SUNLIGHT, GROWING SEASON
THESE INTERACT TO FORM AN
ENVIRONMENTAL COMPLEX
Species experience this environmental complex and respond according to their
‘ecological niche’.
© Ian D. Rotherham 2015
LIMITING FACTORS
Five major groups of factors control the success (productivity) and occurrence (abundance
and distribution) of plants and animals:
1
2
3
4
5
Climatic factors, e.g. solar radiation, temperature, humidity, precipitation, wind,
exposure;
Edaphic factors e.g. soil physical properties, moisture and water relationships, soil
chemistry and nutrient status;
Biotic factors, e.g. the effects of grazing, dunging and trampling by animals; and
burning, cutting, harvesting or transportation by people;
Geological and evolutionary factors, e.g. global tectonics and continental drift, longterm climatic change;
Internal biological factors, e.g. species’ strategies and competitive mechanisms,
successional processes, health, age, condition, genetically based variations in
tolerance or productivity.
Some or all of these factors determine the distribution of a species across the surface of the
earth. Many species have very wide distributions in terms of their tolerance of climatic,
edaphic or biotic controls - such species are said to be eurytypic in their distribution. Others
are very narrow in their range and may only be found in much localised areas with the
particularly favourable conditions in which they thrive. These are said to be stenotypic. If
one factor, such as soil moisture, is taken, then plotting the response of a species along this
environmental gradient in terms of its productivity or abundance will usually result in a
normal distribution or Gaussian curve (Figure 1). The species of plant or animal will be most
abundant, or the individual most productive where soil moisture conditions are at the
optimum. The relative abundance tails off in the areas of increasing stress on either side of
the optimum value. The points in Figure 1 where the species can no longer survive are
termed the upper and lower limits of tolerance.
Figure 1
Similar curves can be drawn for the response of a species to any factor within the tolerance
range of the species with regard to all factors at that site. If any one factor is beyond the limit
of tolerance of that species, then the species will not be able to survive. That factor is known
© Ian D. Rotherham 2015
as the Master Limiting Factor. This is an important concept because often only the one
factor needs to be limiting in order to prevent the growth and establishment of a species.
EXPLAINING DISTRIBUTIONS
Since the study of species distributions is central to biogeography, it is useful to have a model
in which explanation proceeds in an orderly fashion. One such procedure, suggested by
Macan (1963) is illustrated in Figure 2. To explain the absence of a species from an area, we
enter the top of the diagram and proceed down the chain. This was developed specifically for
aquatic species but the principles hold good for a wider interpretation.
Figure 2. Macan’s method for explaining species distributions. (Modified and redrawn from
Macan 1963)
Species in their environments
Animals and plants respond to their environment in different ways. However, many of the
interactions with environmental factors fall into recognisable ‘types’. One way of considering
these, and grouping them into broad categories with similar characteristics is using
‘Resource Allocation Models’.
RESOURCE ALLOCATION MODELS
Although in recent decades this approach has lost favour, it still helps in the basic
understanding of species occurrence and abundance.
© Ian D. Rotherham 2015
In order to complete their life cycles successfully, organisms have evolved general budgeting
mechanisms for the utilisation of energy and available resources. For example, in plants, the
amount of photosynthetic energy allocated to roots, leaves, and reproductive organs, and the
amount of time spent in dormancy, growth, and maintenance, are important attributes that
govern success. Different resource-allocation strategies are applicable in different habitats, and
form a major part in the competitive performance of a species. There is a spectrum of
strategies, two ends of which are called r selection and K selection (Table 2). The letters r and
capital K refer to parameters in the logistic equation for population growth
The r-selected species, also called r-strategist, are species whose populations are governed by
their biotic potential (maximum reproductive capacity, r). Such species make up one of the two
generalized life-history strategies proposed by American ecologist Robert MacArthur and
American biologist Edward O. Wilson. K-selected species - that is, species whose population
sizes fluctuate at or near their carrying capacity (K) - make up the second strategy.
The production of numerous small offspring followed by exponential population growth is the
defining characteristic of r-selected species. They require short gestation periods, mature
quickly (and thus require little or no parental care), and possess short life spans. Unlike Kselected species, members of this group are capable of reproduction at a relatively young age;
however, many offspring die before they reach reproductive age.
In addition, r-selected species thrive in disturbed habitats, such as freshly burned grasslands or
forests characterized by canopies that open abruptly, such as when a forest’s tallest trees have
been knocked down by a windstorm. Temporary environments, such as vernal ponds and
carrion, also harbour r-selected species. Under such conditions, those organisms respond
opportunistically, becoming the first ones to stake their claims to unused resources, such
as nutrients, sunlight, and living space. Although their numbers may soar initially after an
unpredictable event disturbed a habitat in which they reside or can easily colonize, this effect is
often temporary. When other, more-competitive species move in or when the effects of
overcrowding set in, the population will often decline rapidly.
Population growth in r-selected species behaves according to the exponential growth equation:
In this equation, N is the number of individuals in the population and t is time. The factor (1–
[N/K]) is often added to the equation to place an upper limit on population growth by
accounting for environmental resistance.
In ecology, r/K selection theory relates to the selection of combinations of traits in a species
that inversely relate parental investment and the quantity and quality of offspring. Each
selection seems to promote success in different environments.
The r-selection species spread parental investment across many offspring whereas K-selected
species focus theirs on a few. Neither mode of propagation is intrinsically superior. They can
© Ian D. Rotherham 2015
coexist in the same habitat; e.g. rodents and elephants. The r/K selection theory aids the study
of the progression of ecological and historical differences between subspecies for example of
the African honey bee, A. m. scutellata, and the Italian bee, A. m. ligustica.
The theory was popular in the 1970s and 1980s, when it was used as a heuristic device, but lost
importance in the early 1990s, when several empirical studies criticized it. However, more
recently, a ‘life-history paradigm’ replaced the ‘r/K selection paradigm’ and incorporates many
of its important themes.
The ecologists / biologists Robert MacArthur and E.O. Wilson based on their work on island
biogeography coined the terminology of r/K-selection. The concept of the evolution of life
history strategies has a longer history.
In ecology, r/K selection theory, selective pressures are suggested to drive evolution in one of
two generalized directions: r- or K-selection. These terms, r and K, are so drawn from standard
ecological algebra as illustrated in the simplified Verhulst model of population dynamics:
Here, r is the maximum growth rate of the population (N), and K is the carrying capacity of its
local environmental setting, and the notation dN/dt stands for the derivative of N with respect
to t (time). The equation relates the rate of population change to the current population size and
expresses the effect of the two parameters. As the name implies, so r-selected species
emphasize high growth rate, typically exploit less-crowded ecological niches, and produce
many offspring, each of which will likely die ere adulthood (i.e. high r, low K). K, the rate of
population increase, in other words how quickly the initial part of the growth curve climbs, and
K is a ceiling on the population and can be thought of a s the level at which the curve flattens
out. Since K-selected species live in stable environments and exhibit density dependent
mortality, K is considered the ‘Carrying Capacity’ of an environment,
K-selected species display traits associated with living at densities close to carrying capacity,
typically are strong competitors in crowded niches, and invest more heavily in fewer offspring,
each of which will likely mature (i.e., low r, high K). In scientific literature, r-selected species
are sometimes referred to as ‘opportunistic’ whereas K-selected species are described as
‘equilibrium’ ones.
r-selection
Environmental instability or unpredictability favours quick reproduction and renders useless
competitive adaptations. Among the traits that are thought to characterize r-selection are
high fecundity, small body size, early maturity, short generation time, and wide offspring
dispersion.
© Ian D. Rotherham 2015
Organisms whose life history is subject to r-selection, are often referred to as r-strategists or rselected. Organisms that exhibit r-selected traits can range from bacteria and diatoms,
to insects and weeds, to various mammals, particularly small rodents which respond
dramatically and speedily to ecological opportunities.
K-selection
In stable or predictable environments, K-selection predominates as the ability
to compete successfully for limited resources is crucial and populations of K-selected
organisms typically are very constant and close to the maximum that the environment can
bear (unlike r-selected populations, where population sizes can change much more rapidly).
Traits that are thought to be characteristic of K-selection include large body size, long life
expectancy, and the production of fewer offspring, which often require extensive parental care
until they mature. Organisms whose life history is subject to K-selection are often referred to as
K-strategists or K-selected. Organisms with K-selected traits include large organisms such
as elephants, primates and whales, but also smaller, long-lived organisms for example, such
as Arctic Terns.
Continuous spectrum
Although some organisms are identified as primarily r- or K-strategists, the majority of
organisms do not follow this pattern. For instance, trees have traits such as longevity and
strong competitiveness that characterise them as K-strategists. However, in reproduction, trees
typically produce thousands of offspring and disperse them widely, traits characteristic of rstrategists. In other words, the strategy adopted may vary during the species’ lifecycle.
Similarly, reptiles such as sea turtles display both r- and K-traits: although sea turtles are large
organisms with long lifespans (provided they reach adulthood), they produce large numbers of
un-nurtured offspring. Mammalian males tend to be r-type reproducers, whereas females tend
to have K characteristics.
The r/K dichotomy can be re-expressed as a continuous spectrum using the economic concept
of discounted future returns. In this context, r-selection corresponds to large discount rates and
K-selection corresponds to small discount rates.
Ecological succession
In areas of major ecological disruption or sterilisation (such as after a major volcanic eruption,
as at Krakatoa or Mount Saint Helens), r- and K-strategists play distinct roles in the ecological
succession that regenerates the ecosystem. Because of their higher reproductive rates and
ecological opportunism, primary colonisers typically are r-strategists and they are followed by
a succession of increasingly competitive plant and animal species. The ability of an
environment to increase energetic content, through photosynthetic capture of solar energy,
© Ian D. Rotherham 2015
increases with the increase in complex biodiversity as r species proliferate to reach a peak
possible with K strategies.
Eventually a new equilibrium is approached (sometimes referred to as a climax community),
with r-strategists gradually being replaced by K-strategists, which are more competitive and
better, adapted to the emerging micro-environmental characteristics of the landscape.
Traditionally, biodiversity was considered to reach its maximum at this stage, with
introductions of new species resulting in the replacement and local extinction of endemic
species. However, the Intermediate Disturbance Hypothesis posits that intermediate levels of
disturbance in a landscape create patches at different levels of succession, promoting
coexistence of colonizers and competitors at the regional scale.
Status
Although r/K selection theory became widely used during the 1970s, it also began to attract
more critical attention. In particular, a review by the ecologist Stephen C. Stearns drew
attention to gaps in the theory, and to ambiguities in the interpretation of empirical data for
testing it.
In 1981, a review of the r/K selection literature by Parry demonstrated that there was no
agreement among researchers using the theory about the definition of r and K selection, which
led him to question whether the assumption of a relation between reproductive expenditure and
packaging of offspring was justified. A 1982 study by Templeton & Johnson showed that in a
population of Drosophila mercatorum under K selection the population actually produced a
higher frequency of traits typically associated with r selection. Several other studies
contradicting the predictions of r/K selection theory were also published between 1977 and
1994.
When Stearns reviewed the status of the theory in 1992, he noted that from 1977 to 1982, there
was an average of forty-two references to the theory per year in the BIOSIS literature search
service, but from 1984 to 1989, the average dropped to sixteen per year and continued to
decline. He concluded that r/K theory was a once useful heuristic that no longer serves a
purpose in life history theory.
More recently, the panarchy theories of adaptive capacity and resilience promoted by C.S.
Holling & Lance Gunderson have revived interest in the theory, and use it as a way of
integrating social systems, economics and ecology.
In 2002, Reznick and colleagues reviewed the controversy regarding r/K selection theory and
wrote that ‘The distinguishing feature of the r- and K-selection paradigm was the focus on
density-dependent selection as the important agent of selection on organisms’ life histories.
This paradigm was challenged as it became clear that other factors, such as age-specific
mortality, could provide a more mechanistic causative link between an environment and an
optimal life history (Wilbur et al., 1974; Stearns 1976, 1977). The r- and K-selection paradigm
© Ian D. Rotherham 2015
was replaced by new paradigm that focused on age-specific mortality (Stearns, 1976;
Charlesworth, 1980). This new life-history paradigm has matured into one that uses agestructured models as a framework to incorporate many of the themes important to the r–K
paradigm.’
Table 2
Characteristics of r- and K- selected species
r species
K species
Small and short lived
High fecundity
Short generation time
High rate of dispersal
Very variable population density
Time efficient
Opportunistic, exploiting temporary
environments in variable climates
Productive
Large and long lived
Low fecundity
Long generation time
Low rate of dispersal
Stable population density
Food and space resource efficient
Equilibrium species of stable
environments in predictable climates
Efficient
Source: Southwood (1977)
In plants, K-selected tend to be long-lived, have a prolonged vegetative stage, allocate a small
fraction of energy to reproduction and tend to occupy late stages of ecological successions.
At the other extreme, r-selected plants are short lived. They allocate a high proportion of
available resources to reproduction and occupy early stages of successions. Such species are
often described as opportunistic or colonising (Gadgil & Solbrig, 1972). The biogeographical implications of r- and K-selection are considerable. For example, in climates
which vary seasonally and survivors re-colonise habitats each spring, species that are reselected are favoured. In predictable climates with greater uniformity, the higher efficiency of
K-selected species means that they should be more competitive (MacArthur and Wilson,
1967).
Important:
[See also Grime et al. on plant strategy theory and Ellenberg on indicator values and see
notes on ecological successions]
© Ian D. Rotherham 2015
INTRODUCTION TO THE MAIN UK BIOMES
It is likely that there were six main ‘climax’ vegetation types in the British Isles before
widespread human impact:
i) DECIDUOUS WOODLAND - this covered much of the naturally drained lowlands and
slopes up to 500 metres, throughout the British Isles except for parts of northern Scotland.
Much of this was dominated by the Pedunculate Oak (Quercus robur) on poorer soils,
with Small-leaved Lime (Tilia cordata) and Hazel (Corylus avellana), extensive on baserich soils. In many areas, variation in environmental conditions favoured other broadleaved trees such as Ash, Beech, Alder, etc. In upland areas there would be extensive wet
vegetation and in lowland zones, widespread wet fen, wet heath and importantly, wet,
woodland of Alder and Willow.
ii) NORTHERN PINE FOREST - in part of Scotland the short growing season (late spring
and early autumn) affect flowering and seed ripening in oaks and most other broad-leaves.
Extreme winter cold also affected deciduous, southern species. As a result, the original
climax vegetation would have been Scots Pine and Birch with Alder and Willow in wetter
areas.
iii)BLANKET BOG - in sloping upland areas such as the Pennines, Dartmoor, Wales, the
Lake District and Western Scotland, forests were not able to regenerate due to the wetness
of the ground. This wetness also caused leaching of soil minerals so that the soil became
increasingly acid. Bog and moor species became dominant and peat build-up on the
surface. This situation was also affected by climatic deterioration and the onset of wetter
weather.
iv)HEATH - on steep, western-facing, exposed slopes strong winds prevented the growth of
‘forest’. Herbs and shrubs with environmentally ‘dwarfed’ trees therefore became the
dominants. In lowland wet landscapes, wet heaths and bogs were widespread.
v) ARCTIC-ALPINE - after the retreat of the ice certain alpine and tundra plants were only
able to survive in small areas where the low temperature and high winds prevented
colonisation by other plants. Such areas exist only in remote areas of Scotland, Wales and
Northern England at heights of around 1,000 metres and above. In some areas soil
conditions such as metal toxicity also facilitated localised survival of these species.
vi)LOWLAND FEN & MIRE with wet heath and wet woodland - this would have covered
extensive areas of low-lying floodplains and coastal zones.
Following progressive human impacts on the environment, few if any, areas of deciduous
woodland have survived relatively unchanged. The northern Pine forests of Scotland are
© Ian D. Rotherham 2015
reduced in area and changed in character. Blanket bog, heath and small pockets of arcticalpine climax vegetation still survive in the Peak District and the North Pennines. Some small
areas in the south-east Midlands (such as the East Anglian Brecklands), are influenced by
very dry weather and a more continental climate. Climax vegetation here, tends to be heath
and grassland and rarely now, inland sand dunes.
Some river systems, sea cliffs, sand dunes, estuaries, salt marshes, rocky shores and intertidal zones demonstrate relatively small areas of more ‘semi-natural’ habitat-types. Remote
and extremes hill and mountain areas such as boulder slopes and scree slopes also hold
communities that are more ‘natural’.
However, all these communities have been strongly affected by human impacts from grazing
of domesticated animals to burning of vegetation, to harvesting of materials, or the taking of
fuel. All these communities, with a very few tiny exceptions, are essentially ‘semi-natural’ or
‘eco-cultural’ in character. Across the whole of the British Isles, human impacts run deep and
the removal of keystone species such as large carnivores, large wild herbivores, and
mammals such as Beaver, affect everything else.
© Ian D. Rotherham 2015
THE MAIN GENERALISED PLANT COMMUNITY TYPES IN THE UK
WOODLAND
Conifer
Mixed
Broad-leaved deciduous
SCRUB
Very variable
DWARF SCRUB
Heathland (lowland) / Moorland (upland)
ARCTIC-ALPINE
Northern areas and High Mountain Tops
TALL HERB
Often a peripheral or transient community.
GRASSLAND
Many different types defined by conditions, management and
history
Improved / unimproved; enclosed/ unenclosed
Permanent / temporary; upland / lowland
WETLAND
Running water; still water, upland / lowland; oligotrophic /
eutrophic
Marshes, bogs, lakes, ponds, rivers, streams, ditches, canals
COASTAL
NB.
Coastal environments have a diversity of plant and animal
communities, often similar to the terrestrial communities, but
strongly modified by factors such as salinity and exposure.
However, the actual seashore or littoral zone is radically different
from terrestrial systems and is not considered in detail here.
In many urban and post-industrial environments, there may be a complex association of
communities based on the above, but with rather special and unique features, depending
on prevailing conditions and recent history. These may be relatively stable or very
ephemeral. Examples are the so-called ‘urban commons’.
© Ian D. Rotherham 2015
SELECTED BRITISH HABITAT-TYPES
HISTORICAL DEVELOPMENT
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Rotherham, I.D. (2013) Eco-history: An Introduction to Biodiversity and Conservation. The White
Horse Press, Cambridge.
Rackham, O. (1986) The History of the Countryside. Dent, London.
THE POSTGLACIAL HISTORY OF BRITISH VEGETATION: The present flora and
fauna of Britain are mainly the result of migrations and land-use since the last glaciation of the
current Ice Age. Ice-sheets last retreated from Britain approximately 18,000 - 12,000 years ago.
Since then, the climate has warmed progressively and has undergone a series of changes.
Plants and animals migrated back into Britain across land bridges from the continent as the
climate improved. The sequence of species returning reflected the conditions prevailing and
the time since glaciation. Each climatic period was characterised by associated vegetation
communities. These can be determined from deposits of pollen in undisturbed sediments.
The sequence of communities: The arctic wastes and tundra of the late glacial developed
into pine and hazel woodlands by the boreal period. These gave way to mixed forest in the
Atlantic period. The land bridge to the continent was submerged by the rising sea level in
about 5,500 BC i.e. c.7,500 BP. After this, further immigration was more difficult and
effectively impossible for some species.
The Atlantic forest formation but with a diversity of associated ecosystems and communities
as described earlier, represented the ‘climax vegetation’ of Britain. After this time, vegetation
was modified increasingly by human activity. Very few remnants of the original ‘forest’
formation remain. Most ecosystems in Britain are either ‘human-made’ (i.e. anthropogenic)
or ‘semi-natural’, in other words, they are ‘eco-cultural’.
Overall, the flora and fauna of Britain for many groups are relatively impoverished, in both
species and variety, by comparison with those of continental Europe. This is mainly the result
of disruptions caused by glaciations and the problems involved in re-colonisation. Climatic
factors may also play a part in this.
© Ian D. Rotherham 2015
WOODLANDS – TREED LANDSCAPES
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Watkins, C. (1990), Britain's Ancient Woodland: Woodland Management and Conservation. David and
Charles, Newton Abbott.
Rotherham, I.D. (2011) A Landscape History Approach to the Assessment of Ancient Woodlands. In:
Wallace, E.B. (ed.) Woodlands: Ecology, Management and Conservation. Nova Science Publishers
Inc., USA, 161-184.
Peterken, G. (1981) Woodland Conservation and Management. Chapman and Hall, London.
Rotherham, I.D., Handley, C., Agnoletti, M. & Samoljik, T. (eds) (2013) Trees Beyond the Wood – an
exploration of concepts of woods, forests and trees. Wildtrack Publishing, Sheffield, 378pp.
Rotherham, I.D. & Jones, M. (2000) The Impact of Economic, Social and Political Factors on the
Ecology of Small English Woodlands: a Case Study of the Ancient Woods in South Yorkshire, England.
In: Agnoletti, M. and Anderson, S. (eds.), Forest History: International Studies in Socio-economic and
Forest ecosystem change. CAB International, Wallingford, Oxford. 397-410.
Rotherham, I.D. & Jones, M. (2000) Seeing the Woodman in the Trees – Some preliminary thoughts on
Derbyshire’s ancient coppice woods. Peak District Journal of Natural History and Archaeology, 2, 718.
Rotherham, I.D. & Jones, M. (2011) Management issues in urban ancient woodlands; a case study of
Bowden Housteads Wood, Sheffield. Aspects of Applied Biology, 108, 113-121.
Rotherham, I.D. Jones, M. & Handley, C. (eds.) (2012) Working & Walking in the Footsteps of Ghosts
Volume 1: The Wooded Landscape. Wildtrack Publishing, Sheffield.
Rotherham, I.D., Jones, M., Smith, L. & Handley, C. (eds) (2008) The Woodland Heritage Manual: A
Guide to Investigating Wooded Landscapes. Wildtrack Publishing, Sheffield. ISBN 978-1-904098-072. 212pp
Rotherham, I.D. (ed.) (2013) Trees, Forested Landscapes and Grazing Animals: A European
Perspective on Woodlands and Grazed Treescapes. EARTHSCAN, London. 412pp
Rotherham, I.D. (2013) Ancient Woodland: History, Industry and Crafts. Shire Publications, Oxford,
64pp.
Jones, M. (2009) Sheffield’s Woodland Heritage. 4th Edition, Wildtrack Publishing, Sheffield.
Jones, M. (2012) Trees and Woodland in the South Yorkshire Landscape. Wharncliffe Books,
Barnsley.
Rackham, O. (1980) Ancient Woodland: its history, vegetation and uses in England. Edward Arnold,
London. (2003 Second edition by Castlepoint Press).
Rackham, O. (1986) The History of the Countryside. Dent, London.
Features of woodlands: At present, woodlands and forest cover only about 15-10 percent of
the area of Britain but they are more abundant in certain areas such as for example, the
Weald. For example, they cover nearly 8 percent of south-eastern England. In Britain, most
treed landscapes currently recognised as ‘woodlands’ are either in part at least, planted or are
derived from planted woodlands. There are extensive areas of young secondary woods such
as re-colonising Birch on heaths and moors. Some woods have small areas of relatively
‘natural’ or ‘semi-natural’ cover as ‘semi-natural, ancient woods’.
Practically all of these semi-natural ecosystems have undergone some management for timber
production or for hunting. The functioning of forest ecosystems is described later. Attention
is given here to the types of woodlands in Britain and to the management practices, which
have been important in their formation.
Composition of deciduous woods: These represent part of the European temperate forest
type. The main dominants of British deciduous woodlands are Oak, Beech, Ash, Birch and
© Ian D. Rotherham 2015
Sycamore with Holly, Willow, Hazel and Hawthorn as the principal understorey shrubs.
Typically these woodlands contain four layers or strata
The two species of oak occurring naturally in Britain, Quercus petraea (the sessile oak) and
Quercus robur (the Pedunculate Oak or English Oak) are the most important dominants and
can grow in a variety of site conditions. The accompanying species vary with differences in
soil, nutrients and drainage.
Most British woodlands are dominated by one or two species of tree. In many cases, this is a
legacy of either planting policy or selective felling in the past.
Regeneration of deciduous woods: Deciduous woodlands in Britain tend to have even-aged
canopies and lack natural regeneration. This is due partly to pressure from human
interference and partly to the nature of the plants themselves.
(a) The dominant trees are slow to mature. Oak and Beech may be 40 or 50 years old
before they flower.
(b) Seed production of the dominants is variable and spasmodic.
(c) It is difficult for seedlings to become established and to survive under the canopies
because of shading, root competition and damage from herbivores.
Ancient woodlands: Some small areas of woodlands in Britain may have tenuous links back
to the original ‘wildwood’, and others are remnants of royal ‘forests’ and aristocratic ‘chases’
established by the Normans for hunting. In the twelfth century, over one-third of the country
was covered by royal forests, but this does not necessarily imply woods. Many were
extensive heaths, moors or fens. Most have been removed for agriculture but some areas,
such as the New Forest and Sherwood Forest, have areas which remain relatively
undisturbed, but which now suffer from issues related to ‘cultural severance’. These contain
ancient trees and many rare species of plants and animals. (NB. The term ‘forest’ historically
included areas of heath, commons and farmland, along with woodland – these were areas
subject to the Forest Laws).
Managed Woodlands: Many deciduous types of woodland have been managed for wood or
underwood production. Although this activity tends to be uneconomic today, evidence of it
can be seen in the structure of the woodlands and in the archaeological evidence of the trees,
the soils and the ground floras. Two practices were most important. In both of them, usable
timber is obtained by suppression of the terminal bud i.e. the cutting of the leading shoot or
trunk by coppicing or pollarding.
a) Coppicing: This began in earnest sometime in the Middle Ages, though its history goes
back to the Romans and earlier. It continued as an economic practice until after the Second
World War. The method produces tall, thin, straight poles for fences, firewood, hurdles and
charcoal. Hazel, Oak or Sweet Chestnut are cut to ground level. Re-growth is rapid and
produces straight branches. Traditionally, the coppiced wood is grown beneath a canopy of
© Ian D. Rotherham 2015
standard trees, either oak or ash, spaced at a density of 6 per hectare (twelve per acre) so that
their crowns do not overlap. The standards produce wide boughs used originally for ships’
timbers. The coppice was cut every 10 to 25 years dependent on the location and the desired
crop. Many coppices have rich communities of herbaceous plants.
b) Pollarding: Several deciduous trees such as beech and oak regenerate their canopies if the
branches are cut off at the top of the trunk. This re-growth produces a dense crown of small
timber at a height safe from browsing animals. Pollarding was carried out extensively from
the Middle Ages to about the mid-nineteenth century. Ancient pollards are usually found in
historic parks, chases etc ...
c) Plantations: Since the 1700s, many areas have been planted with trees and many woods
have been re-planted. These may be with hardwoods such as Sycamore, Oak or Beech, or
with any of a range of conifers from native Scots Pine to exotic Siktka Spruce or European
Larch. Many lowland woods were established or re-planted in the 1700s or 1800s with Oaks
grown in European nurseries and genetically distinct from the native English Oaks.
As many plantations were grown on land previously used for agriculture, a true woodland
flora and fauna takes a long time to become established. The plantations may be important
habitats for many species, especially in regions of Scotland for example, where woodland is
sparse. Red Squirrels, Pine Martens, Wild Cats and Crossbills have all increased in numbers
because of afforestation. Mixed plantations or coniferous stands may favour birds of prey
such as Sparrowhawk and Goshawk, and smaller birds like Siskin and Redpoll.
If conifers are planted on old deciduous woodland sites the change in nutrient cycling induces
changes in soil characteristics leading to increased acidity and decreased diversity of soil
fauna.
Coniferous woods: Native coniferous woodlands (Scots Pine) with associated deciduous
trees) in Britain represent an ecotone between the temperate deciduous forest and the boreal
forest. They occur mainly on well-drained acid soils. Few areas of ancient coniferous forest
remain, as for example at Rothiemurchus in the Spey valley, Scotland.
Conifers regenerate successfully in many places. The dominants mature more quickly than do
those of deciduous woods, and have a higher net productivity in the early years of growth.
This, together with the lightness of the wood and its good physical qualities for working,
make conifers important commercially. The tree species that regenerate in the ‘wild’ in
Britain include many of the exotic ones like European Larch, Sitka Spruce, Norway Spruce
and others. This presents site managers with interesting questions and challenges about which
species to select and allow and which to remove.
© Ian D. Rotherham 2015
HEATHLANDS and MOORLANDS
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

Rotherham, I.D. (1995) Urban Heathlands - their conservation, restoration and creation. Land
Contamination and Restoration, 3, (2), 99-100.
Rotherham, I.D. (2011) Habitat Fragmentation and Isolation in Relict Urban Heaths - the ecological
consequences and future potential. In: Rotherham, I.D. & Bradley, J. (eds) (2009) Lowland Heaths:
Ecology, History, Restoration and Management. Wildtrack Publishing, Sheffield.
Rotherham, I.D. & Bradley, J. (eds) (2011) Lowland Heaths: Ecology, History, Restoration and
Management. Wildtrack Publishing, Sheffield.
INTRODUCTION: Heathland and moorland vegetation is dominated by evergreen dwarf
shrubs of the heather family (Ericaceae). Trees, tall shrubs and extensive grass turf maybe
absent. Some moors may be dominated by grass and rush species. Heathlands were very
widespread in northern Europe until the early twentieth century. They formed a distinct
community type often used for common grazing land. Traditionally, managed heaths are
burnt every few years to remove old growth and to encourage new shoots for herbage. The
area of heathlands has decreased greatly since the nineteenth century as their use has become
uneconomic. They were often on relatively unproductive land, and managed as ‘commons’.
If they are not burnt or grazed, succession takes place and they develop into woodlands.
ENVIRONMENTAL CONDITIONS & HEATHS
(a) Climate: Heathlands occur in areas of moist temperate climate with mild winters where
at least 4 months have average temperatures above 10C. The mean temperature of the
warmest month is usually below 22C. Relative humidity is relatively high and periods of
drought are short.
(b) Soils: These are usually freely drained and acidic. Heathlands are associated with podsols
with thin peat layers at the surface.
(c) Exposure: Heath plants can tolerate extreme exposure, as for example on cliffs and
mountains, but they cannot tolerate shading from taller plants.
(d) Grazing and burning: The plants can withstand these pressures because of their
morphology and life cycles.
Status: In a few cases, such as on exposed cliffs or on mountains above the treeline, heaths
are the natural climax vegetation. However, most heathlands are the result of human activity.
The development of the ecosystem to its full biotic potential is checked by the action of fire
and grazing. The heathlands are unstable systems and undergo rapid change if the arresting
factors are removed.
© Ian D. Rotherham 2015
Origins: Many theories have been formulated to account for the origins of heathlands. The
importance of human action in maintaining the heaths is undeniable but controversy existed
as to how heathlands developed in the first instance. Clearly, they are not determined
climatically since the climate type also supports forests or treed landscapes. Similarly, the
associated soils are capable of supporting trees.
(a) Seral theory: In the 1940s, many workers, including the British plant geographer
Sir Arthur Tansley, thought that the heaths were a seral stage in the postglacial
development of vegetation communities. They considered that heathland areas
developed directed from tundra without intervening forest. These workers were
strongly influenced by the concept of succession.
(b) Degenerate theory: As early as 1901, Graebner proposed that the heathlands of
northern Germany were degenerate systems derived from forest by progressive
felling. The development of pollen analysis in the 1950s produced evidence to
confirm this view. Dimbleby (1962) has shown that many of the British
heathlands were formed from forests in the Atlantic and sub-boreal periods. The
area of heathland continued to expand until the eighteenth century.
It now seems that many heaths and moors share common origins with woods, fens and bogs,
and many were in reality unenclosed ‘wooded commons’ and ‘wood pastures’. Over time, the
tree element has been reduced by removal and use and intensive grazing has prevented
regeneration. However, the presence of a strong ‘woodland element’ in the ground flora is
evidence of this historic link. These heaths link back to the more open, fluid landscapes
described by Vera for the primeval European environment. It is now suggested that these and
related communities survived in areas of the landscape which remained unenclosed after the
Statute of Merton in 1235 AD. [*See work on Shadow Woods & Ghost Woods]
HEATHLAND AUTOTROPHS - VEGETATION
(a) Vegetation: Heathland communities are homogeneous and usually lack diversity in their
flora. British heaths have three main dominants, Ling or Heather (Calluna vulgaris), which
occurs throughout, Bell Heather (Erica cinerea) which prefers drier areas, and Cross-leaved
Heath (Erica tetralix) which prefers wetter areas. These form a canopy beneath which few
plants are present in association.
Understorey or dominant plants include Bilberry (Vaccinium myrtillus) and calcifuge grasses
such as Mat Grass (Nardus stricta) and Wavy Hair-grass (Deschampsia flexuosa) as well as
broad-leaved herbs, such as Sheep’s Sorrel (Rumex acetosella) and Heath Bedstraw (Galium
saxatile). Mosses and lichens are prolific, growing directly on the soil or peat surface.
(b) Adaptations to the habitat: Heather possesses a number of features, which make it very
successful in heathland.
© Ian D. Rotherham 2015
(i) Germination: Seeds are produced in great numbers and have high percentage viability.
They have staggered dispersal and germination that is development is delayed in some seeds
so the potential for regeneration is conserved. Germination can take place over a wide variety
of conditions.
(ii) Burn resistance: Exposure to moderate heat, as from a local burning, accelerates
germination of seeds. Adult plants can re-grow from the roots if aerial parts are burnt off.
(iii) Desiccation resistance: Adult plants have xeromorphic leaves. Stomata are located in a
groove on the underside of the leaf that can be opened or closed to control transpiration.
Heather is adapted physiologically to tolerate low water content in its tissues.
(iv) Calcifuge habit: Heather achieves vigorous growth in soils of pH 3.5-6.5.
(v) Mycorrhizal roots: Heather roots are infected by a fungus that give enhanced nutrient
uptake in this nutrient-stressed environment.
HEATHLAND HETEROTROPHS: The low growing homogeneous vegetation provides
little variety of microclimates and habitat potential. However, since heathlands are on soils,
which warm up rapidly, they have rich invertebrate, reptile and bird fauna.
(a) Invertebrates: Only a few invertebrate faunal groups are genuinely scarce on heathlands.
These are molluscs, which are limited to calcareous areas for shell growth; earthworms,
which cannot tolerate high acidity; and woodlice, which cannot tolerate very dry conditions.
Most other groups of invertebrates such as the ants, weevils, spiders, wasps and mites are
prolific, and occupy a variety of niches and trophic levels. For example, within the beetle
group, some characteristic species (such as the Heather Beetle) are herbivorous, and some
(such as the Tiger Beetle) are predatory.
(b) Vertebrates: The main grazers on heathlands are sheep, cattle, ponies and deer.
Ecologically the most interesting groups present are the reptiles and the birds. Some of our
rarest reptiles, such as the Smooth Lizard, are confined to the warm soils of the southern
heathlands. The prolific invertebrate fauna provides abundant food for birds. Many rare
species, such as the Dartford Warbler, feed and nest in the southern heathlands. Others such
as the Honey Buzzard and the Hobby feed in the heath but nest in adjacent woodlands.
Heaths in upland areas are important for game birds like Red Grouse, Black Grouse and
Ptarmigan, and birds of prey such as Merlin, Hen Harrier and Peregrine.
HEATHLAND FUNCTION
(a) Productivity and food chains: Primary productivity is low especially when the heath
dominants are old. The standing crop at both the primary and secondary levels is small,
© Ian D. Rotherham 2015
reflecting the low energy flow through the system. Food chains are short but complex webs
exist, particularly those involving invertebrates.
(b) Nutrient cycling: This is low and impoverished with many net losses from the system.
Decomposition occurs slowly in the acid conditions as leaf litter decays mostly because of
fungal action. Raw humus accumulates to form a peaty layer on the soil surface. ‘Moorlands’
occur where evapotranspiration is exceeded by precipitation, and on free-draining soils have
a limited accumulation of undecomposed organic material. Grazing and burning extract
nutrients from the ecosystem accentuating the nutrient deficiency. Heathlands are particularly
lacking in calcium. Continual removal of supplies from the system by grazing without return
of nutrients leads to increased acidity.
Heaths and moors have significant components of grasslands, of fens, bogs & mires, and
woodlands.
© Ian D. Rotherham 2015
GRASSLANDS
INTRODUCTION: British grasslands can be divided into three main types:
(a) Calcareous or alkaline, growing on base-rich chalk or limestone soils.
(b) Acidic or siliceous, growing on the soils of acidic rocks or in highland areas.
(c) Neutral or mesotrophic, growing on soils of moderate pH values and sharing some of
the features of both of the other types.
The grasslands vary greatly in their ecological interest and nature conservation or heritage
value. Some have been sown relatively recently whilst others are of great antiquity and have a
long history of management. The calcareous grasslands, especially those on chalk, are the
most important for their flora and associated fauna. They contain many of Britain’s rarest
species of plants and of invertebrates. Many ancient grasslands have high archaeological and
heritage interest – often overlooked by ecologists
CHALK & LIMESTONE GRASSLANDS
Location: Chalk deposits are widespread in southern England and north-west France. Most
develop alkaline soils suitable for calcareous grasslands. In Britain, chalk grasslands are
found on the North and South Downs, the Chilterns, and Salisbury Plain, together with parts
of Wiltshire, Berkshire and Dorset. The Lincolnshire and Yorkshire Wolds are also chalk
areas.
Limestone occurs in areas such as the Peak District, the Yorkshire Dales, south Cumbria, and
in a strip of Magnesian Limestone running north-south through England from the
Nottinghamshire and Derbyshire, though Yorkshire and into County Durham.
Environmental conditions:
© Ian D. Rotherham 2015
(a) Soils contain a high proportion of free calcium carbonate and exchangeable calcium
giving them high pH values. Most are shallow rendzinas with little organic matter in the ‘A’
horizons. The soils are freely drained and well aerated.
(b) The porosity of chalk and its associated soils leads to water deficiency. The grasslands
have little potential for microclimatic amelioration so that the biotic components of the
system are prone to desiccation.
(c) Grazing is an important factor in the maintenance of the grasslands. Vegetation must
withstand trampling and nibbling especially from sheep, cattle and rabbits.
Origins and status: Evidence from pollen analysis and archaeology suggests that the
Atlantic forest cover was removed from many chalk areas by 2,500 BC i.e. c. 4,500BP.
Many grasslands developed and were maintained by human activity. Originally, the
grasslands were grazed by a variety of domestic stock including oxen and pigs. Some
grasslands are a result of altitudinal effects, or extreme conditions such as coastal salt spray
or seasonal flooding, regular natural disturbance, or natural levels of grazing.
In Britain, a tradition of sheep grazing evolved, as wool became an important commercial
fibre. If grazing stops, the grasslands mostly undergo secondary succession and the
woodlands develop via scrub. This has occurred in many places since the eighteenth century
although the process was stored or halted on many sites due to rabbit grazing - until the
population collapse associated with myxomatosis in the 1950s - 1970s. Woodlands
dominated by beech, yew, oak or ash are abundant now in areas formerly occupied by chalk
grassland.
CHALK GRASSLAND AUTOTROPHS
(a) Vegetation: Communities are extremely rich and diverse. It is estimated that over half of
the species of seed plants and ferns in Britain grow in this habitat. Over fifty species of plant
are confined exclusively to calcareous grasslands, including some of the rarest orchids. The
species composition and abundance varies between different areas according to differences in
local climate and land-use, but all chalk grasslands have short springy turf. Throughout the
main dominant grasses are Sheep’s Fescue (Festuca ovina), Red Fescue (Festuca rubra),
Crested Hair-grass (Koeleria cristata) and Quaking Grass (Briza media). These grow with a
great variety of other grasses, sedges, broad-leafed herbs and mosses. However, they all have
certain features in common and display similar geographical affinities.
(b) Adaptations to the environment: the exacting environments of the chalk grasslands
have produced convergence in the features of the plants.
© Ian D. Rotherham 2015
(i) Many of hemi-cryptophytes: These have their growing points close to the ground and
can sprout again if the shoots are grazed.
(ii) Rosette habit: Approximately 35 percent of the chalk sward species grow in a rosette
form. This is resistant to grazing and trampling and helps to avoid desiccation.
(iii) Mat habit: This adaptation is also very frequent. Extensive horizontal branching
eliminates competition and aids the plant in surviving grazing.
(iv) Xeromorphism: This is important in this dry habitat. Features include narrow or rolling
leaves, hairs to reduce transpiration and thick, waxy cuticles.
(v) Storage organs, such as bulbs, are prolific and act as a buffer against environmental
stress.
(vi) Long life: Most species are perennial. The sward forms a dense mat, which precludes
invasion or re-establishment seedlings.
(vii) Calcicoles: Many of the chalk grassland plants re restricted to this habitat because they
are calcicoles; these are species limited to alkaline soils. They may be either chemical
calcicoles, that is, restricted to this soil type because of its chemical properties, or physical
calcicoles, that is, restricted to this soil type because of its physical properties (these include
free drainage, warmth and good aeration). Many of the British physical calcicoles are at the
limit of their distribution range in this country. Elsewhere they can grow on a variety of soil
types but here they are restricted to the most favourable habitat.
(viii) Mycorrhizal Fungi: Many grassland herbs and grasses have root-infecting fungi, which
are very important to their metabolism. Indeed, chalk grassland plants are often joined in
complex inter-species nutrient transfer networks by vesicular-arbuscular mycorrhizas.
RELATIONSHIPS WITH CLIMATE
(a) Geographical affinities: Several different geographical elements combine to form the
flora. Many of the species of the continental elements are adapted to warmer drier climates.
(b) Changes in flora in relation to local climate: The geographical elements display
slightly different distribution patterns within the chalk grassland habitats. This can be seen
both on regional and local scales. Species with marked southern affinities are most prolific in
the south-east. Widespread European and northern continental species are most prolific in the
northern grasslands. North-facing slopes tend to have very different communities than southfacing slopes because the latter become very hot and dry in summer, in comparison with the
cooler, wetter north-facing areas.
© Ian D. Rotherham 2015
Chalk grassland heterotrophs: The invertebrate fauna of chalklands is extremely rich and
diverse. The varied vegetation communities present many niches. Soils warm up quickly
during the day and can support many species, which are on the edge of their distribution
range in Britain.
Many of the invertebrates are specialists being restricted to a few types of food. For
example, the Large Blue Butterfly (Maculinerea arion) feeds on Wild Thyme when young,
then on ant larvae. The Small Blue Butterfly feeds specifically on the uncommon Kidney
Vetch (Anthyllis vulneraria); such specialisation making them vulnerable if habitats change.
The main grazers are Sheep and Rabbits; both feed selectively showing distinct preferences
for particular plants.
ECOSYSTEM FUNCTION
(a) Productivity and food chains: Primary productivity is generally low because of the
habitat constraints. The amount of biomass in the standing crop of autotrophs is small, but the
variety of components provides many ways for animals to obtain food. Food chains are
complex with many intimate relationships and narrow niches. Food webs involving
invertebrates can have many trophic levels because little energy is required to support each
individual.
(b) Nutrient cycling: Dead organic matter decays rapidly in this habitat. Most decomposition
occurs through bacterial action and produces mull humus in the soil. The majority of plants
are perennial so nutrient cycling may be slow. The ecosystem does not suffer great
deficiencies of nutrients except in very dry areas when some elements, such as exchangeable
potassium, may be lacking.
Table 1. GEOGRAPHICAL ELEMENTS IN THE FLORA OF BRITISH CHALK
GRASSLANDS
Approximate
percentage of
flora (%)
Element
Associated
climate
Example
species
Hoary Plantain
(Plantago media)
55
Wide European
temperate
25
Southern continental
12
Continental
hot dry
summers,
cool winters
Traveller’s Joy
(Clematic vitalba)
Stemless Thistle
(Cirsium acaule)
4
Northern continental
3
Southern oceanic
warm,
Chalk Milkwort
© Ian D. Rotherham 2015
1
Northern oceanic
moist
(Polygala calcarea)
cool, moist
Wild Thyme
(Thymus drucei)
SALT MARSHES
These are areas of open grass- or herb- dominated communities where relatively natural
processes predominate. Whilst the alternating conditions of wet and dry, and of saltwater and
freshwater, present major challenges for both plants and animals, these are incredibly
productive ecosystems. Primary production is subsidised or supplemented by sediments rich
in nutrients and in organic materials deposited from both land and sea.
Introduction: Salt marshes are areas subject to periodic eroding by the sea. They occur on
coasts with shallow gradients and in estuaries behind spits. Sediments are deposited on the
marsh by the action of tides and drainage from inland. The sediments become established by
the saltmarsh vegetation, so that deposits accumulate and the marsh grows seaward as the
land level rises.
ENVIRONMENTAL CONDITIONS: All habitat factors vary over the marsh in relation to
distance from mean sea level.
(a) Tides: The habitat is flooded at each high tide and is exposed at low tide. This alternation
produces environmental stresses for life. For example, flooding reduces the aeration of roots
and the photosynthesis of submerged plants, whereas exposure may lead to desiccation.
(b) Salinity: This varies over the marsh in both space and time. Most importantly, it varies
with the state of the tide, rainfall, and distance from drainage creeks, and runoff from inland.
The presence of salt inhibits the uptake of nutrients and water.
(c) Soils: These are generally formed on a sand base. Particle size depends on the conditions
for sedimentation, including distance from creeks. Coarser materials are deposited first as
finer materials are carried further. Because of this, banks build up on edges of creeks. The
soil never becomes completely waterlogged. There is always a shallow aerated layer just
below the surface even during flooding.
© Ian D. Rotherham 2015
(d) Exposure: The amount of time that the marsh surface is exposed to air each day varies
with distance from the mean sea level and the drainage creeks.
SALT MARSH AUTOTROPHS - VEGETATION
(a) Vegetation communities: Very few higher plants can tolerate the saline conditions so the
flora of salt marshes is very specific. Communities vary with environmental factors.
Vegetation tends to be zoned from the low water level inland reflecting time of exposure and
salinity. Each zonal community can be regarded as a sere in a succession from bare mud or
sand to dry land. The species of each sere tolerate the conditions in that tidal range. The
communities migrate seaward as the marsh grows.
The broad zonal pattern of communities is complicated by the presence of sub-environments.
Creeks, shallow depressions (saltpans) and other surface features cause local varieties in
environmental factors.
ADAPTATIONS TO THE ENVIRONMENT
(i) Resistance to salinity: Halophytes are adapted to cope with stresses imposed by salinity.
(ii) Reproduction. Annuals are rare except in the narrow pioneer zone, which is kept open by
tidal action. The majority of marsh plants are short-lived perennials. This strategy seems to be
the best compromise. The annual habit has the disadvantage of having to become re-established
each year. The long-lived perennial habit does not give the opportunity to change location
frequently in response to changing conditions as the marsh grows.
(iii) Resistance to mechanical drainage: Plants must be able to tolerate the force of tidal
action. Many have narrow, smooth leaves, which present little resistance to water movement.
Some algae have gelatinous secretions that bind the plant into the mud.
Salt marsh heterotrophs: Bacteria and fungi are the most important consumers of energy in
salt marshes. Large herbivores are generally lacking, though Ponies or Sheep graze some
areas. The mud supports abundant invertebrate animals including snails, mussels and worms.
These all have euryphagic habits (i.e. they consume a wide variety of foods) and exploit a
wide range of food all year. The invertebrates form a food supply for birdlife.
ECOSYSTEM FUNCTION
(a) Productivity: Salt marshes are among the most productive ecosystems in the world. In
some cases, primary productivity is between 1,000 and 2,500 kcal/m2/year. These high rates
are achieved because the marshes contain abundant nutrients ‘subsidized’ greatly by deposition
of materials from the sea and from rivers. Salt marsh plants expend a lot of energy in
© Ian D. Rotherham 2015
respiration required to power the halophytic adjustments. In spite of this, net primary
productivity is still in the order of 1.4 per cent of incident light energy. The standing crop of
perennials is augmented by the growth of algae, which may form 25 per cent of the total plant
biomass.
(b) Food chains: Herbivores are scarce in the ecosystems. Most autotroph biomass is
consumed by bacteria and fungi so that the flow of energy is short circuited. Food chains are
reduced but may be complex because of the wide niches. The rate of energy flow through the
system is high.
(c) Nutrient cycling: The salt marsh acts as a trap for nutrients brought by inland drainage and
the tides. The abundant nutrients are cycled quickly. Decomposition in marshes is poorly
understood but does seem to be aided by the mechanical breakdown by tides. Similarly,
nutrients are moved throughout the marsh by tidal action. Dead grasses may be decomposed
slowly but algae are broken down quickly to give a continual turnover of nutrients.
Some salt marsh plants experience deficiencies of trace elements. This is due to two reasons.
(i) Anaerobic conditions cause sulphates to be changed to insoluble sulphides so that nutrients
such as iron, held in these compounds, are unobtainable.
(ii) The presence of salt causes ion antagonism or competition, that is, the uptake of some
nutrients is inhibited by the presence of others. Many halophytes have low requirements for
iron and manganese as an adaptation to these conditions.
SAND DUNES
Sand dunes form on coasts where large expanses of land are exposed at low tide and where the
shoreline topography is gentle. Windblown sand is stabilised by vegetation and accumulates to
form dunes. Historically, sand dunes also formed extensively in localised inland areas – such
as the Brecks in East Anglia, and the Cover Sands areas of North Lincolnshire.
Dune systems depend on energy in the form of exposure to wind, and on a supply of material
to be blown i.e. sand. The character of the ecology depends on the type of sand, which is
mostly calcareous, but may rarely be acidic (from glacial deposits), in which case the
associated species may be particularly interesting. Whilst these are environments in which the
ecology is clearly dominated by natural processes, many dune areas where deliberately and
artificially created in centuries from the medieval up to the nineteenth century, as land
management and protection schemes.
In order to be maintained sand dunes require space and the freedom for mobility, which people
have restricted over recent centuries. In the 1700s, 1800s, and 1900s, many sand dune systems
were planted with conifers in order to ‘stabilise’ them. In medieval times and later, dunes were
important as Rabbit warrens with exotic Rabbits imported from the Mediterranean. Today,
© Ian D. Rotherham 2015
these apparently ‘natural’ ecosystems are often dominated by Rabbit grazing and affected by a
range of invasive, alien plants.
ENVIRONMENTAL CONDITIONS
(a) Sand mobility: The dune habitat is characterised by shifting sand. This may bury plants,
expose roots, cause abrasion and change the surface relief thus altering the microclimates.
(b) Temperatures: Sand is a poor conductor of heat. Surfaces are exposed to extremes of
temperature but the sand acts as a buffer minimising variations in temperature within the dune.
(c) Water supply: Dunes are extremely arid because surface water drains away quickly.
(d) Wind velocity: Sand dunes are exposed to onshore winds. These accentuate the problems
of desiccation and cause mechanical damage to plants.
SAND DUNE AUTOTROPHS
(a) Vegetation communities: The flora contains a proportion of characteristic species but it is
not as specific as that of salt marshes. Consequently, it is a much richer flora. The vegetation
includes a large number of species with different degrees of tolerance to sand covering and
exposure to environmental extremes. These form various communities related to the distance
from the sea and the age of the dune. The communities can be viewed as a succession sequence
from bare sand on the beach to woodland inland. The precise plant communities depend very
much, on whether the pond itself is base-rich or less commonly, base-poor.
(b) The dune sequence: The succession proceeds through three main phases (i – iii). These
may not all be present in one location because of erosion, habitat change or land-use.
(i) Fore dunes or embryo dunes are formed by low accumulations of sand near to high water
level. Typically, they are colonised by Sea Couch Grass (Agropyron junceiforme) and Marram
Grass (Ammophila arenaria). Vegetation is sparse.
(ii) Mobile dunes still have large areas of bare sand. Marram Grass is the main coloniser. This
has extensive root systems, can stand desiccation and grows up through the sand as it is
covered. For these reasons, Marram is the principal agent in stabilising the dunes. Mobile
dunes may be divided into yellow dunes, which have little organic matter in the soil, and the
older grey dunes, which have a shallow layer of organic matter near the surface.
(iii) Fixed dunes have a complete vegetation cover. Sand is stabilised by the closed
community. Marram, which needs a constant supply of fresh sand to grow, becomes less
frequent. The vegetation is dominated by grasses, such as the Fescues, and low growing herbs.
This dune grassland may develop into dune scrub or heath. Ultimately, woodlands colonise the
area.
© Ian D. Rotherham 2015
(iv) Dune slacks: Wind erosion in the mobile dunes may cause ‘blowouts’ which reach down
to the water table. These dune slacks often have small ponds or marshes in them. Vegetation is
usually halophytic but may contain some freshwater species.
Sand dune heterotrophs: Large herbivores apart from Rabbits which graze mainly on the
dune pasture communities, are scarce. If grazers are absent, grasses and sedges grow more
luxuriantly and shade out broad-leafed herbs. Invertebrates are prolific and diverse, particularly
the arthropods. Worms may be common in the due slacks. Birds form an important component
of the system; they feed on the invertebrates and carry the seeds of many of the scrub species in
from other areas.
Ecosystem function: Productivity is low because of the sparse vegetation and harsh
environment. Food chains are short but may involve complex food webs. Small amounts of
nutrients are cycled, especially in the early stages of colonisation. Decomposition occurs
rapidly. Nutrients may be locked in plants for long periods in the later seral stages when
perennials predominate.
Maintenance: The sand dune system is inherently unstable. The surface sward can be eroded
easily by trampling or excessive grazing. Once the vegetation has been removed the ecosystem
reverts to the mobile stages of development. In areas where sand dunes suffer pressure from
recreational activities, attempts are made to prevent sand movement. These include placing
matting on the surface and planting Marram Grass to stabilise the sand.
© Ian D. Rotherham 2015
WETLANDS: MIRES - FENS & BOGS.
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Rotherham, I.D. (ed.) (1999) Peatland Ecology and Archaeology: management of a cultural landscape.
Wildtrack Publishing, Sheffield.
Rotherham, I.D. & Harrison, K. (2009) South Yorkshire Fens Past, Present and Future: Ecology and
Economics as Drivers for Re-wilding and Restoration? In: Hall, M. (ed.) Greening History: The
Presence of the Past in Environmental Restoration. Routledge Publishing, London, 143-153.
Rotherham, I.D. (2010) Yorkshire’s Forgotten Fenlands. Pen & Sword Books Limited, Barnsley. 181pp.
Rotherham, I.D. (2008) Landscape, Water and History. Practical Ecology and Conservation, 7, 138-152.
Rotherham, I.D. (2008) Floods and Water: A Landscape-scale Response. Practical Ecology and
Conservation, 7, 128-137.
Hawke, C. & Jose, P. (1995) Reedbed Management for Commercial and Wildlife Interests. RSPB, Sandy,
Bedfordshire.
Rotherham, I.D. (2013) The Lost Fens: England's Greatest Ecological Disaster. The History Press,
Stroud.
These are ecosystems in which the vegetation is rooted in wet peat; base-rich and eutrophic i.e.,
FENS, or base-poor and oligotrophic i.e., BOGS.
BOGS
INTRODUCTION. Bogs occur in areas of poor drainage. The soil is acid and permanently
waterlogged. These conditions promote anaerobic decay, which is very slow. This process
leads to the accumulation of organic matter forming deposits of peat, which may be several
metres thick.
Most British bogs have been drained or destroyed. Some remain in western Scotland, northern
England, Wales and certain places in southern England such as the New Forest.
TYPES. Bogs can be divided into three main types.
(a) Valley bogs. These occur in valleys and local depressions where there is some impediment
to local drainage. The valley bog may have a stream flowing through it. This transports
nutrients into the bog and may decrease the acidity along its course.
(b) Raised bogs. These have convex surfaces built up by the accumulation of peat. They may
develop on valley bogs so that the depression is filled by the growth of the bog. The surface is
gently domed from the centre but is bounded by a steep slope or rand at the edge. Raised bogs
frequently have a water course or lagg round the periphery.
(c) Blanket bog. This develops on slopes of gently gradient in areas of high rainfall. It is
extensive in many of the upland areas of Britain such as the western Pennines, Dartmoor and
western Scotland.
© Ian D. Rotherham 2015
AUTOTROPHS - BOG VEGETATION.
(a) Bog mosses: Sphagnum mosses are the most important dominant plant type, and include
about twenty species in Britain. Each one has a definite tolerance limit to acidity and
waterlogging so they are useful environmental indicators. The growth of the bog mosses
induces acidity in the bog since the sphagnum cell walls produce carboxylic acid. Dead
biomass from the sphagnum is largely responsible for the accumulation of peat.
(b) Valley bogs: Vegetation communities usually display concentric zonation in relation to the
distance from the edge of the bog and the central drainage stream. Wet heath grows on the edge
of the bog and merges into communities dominated by the bog mosses with Purple Moor Grass
(Molinea caerulea), sedges and bog plants such as the Bog Asphodel (Narthecium ossifragum).
The central area may have a fen-like community, that is, one that likes nutrient-rich, alkaline
conditions. Willow and Alder grow to form a carr along the stream course.
(c) Raised bogs: Characteristically the surface has a series of hummocks and hollows.
Communities are dominated by Cross-leaved Heath (Erica tetralix), Bog Myrtle (Myrica gale),
bog mosses, and sedges. The different species segregate in relation to the micro-relief because
of its influence on drainage. The bog surface grows by a series of micro-successions in the
hummock complex. Hollows are filled by the accumulation of peat and eventually form new
hummocks. Hummocks stop growing as they dry up above the water table and eventually form
hollows between the new hummocks. In this way, the whole surface is grows upwards, and the
water table is raised with the surface because the peat and the growing mosses retain a lot of
water.
(d) Blanket bog: The species are mainly the same as those of raised bogs but sphagnum
mosses may not be as prolific. Deer Sedge (Tricophorum caespitosum), Cotton Grass
(Eriophorum angustifolium and vaginatum) and Purple Moor Grass predominate. Cross-leaved
Heath and Bog Myrtle are present throughout except in the wettest areas. Hummocks do not
usually develop in a blanket bog, but in reality, blanket mires may grade into valley bogs and
can also develop raised elements.
BOG PLANT ADAPTATIONS.
(a) The problem of waterlogging: Bog plants grow with their roots in permanently
waterlogged ground. This presents problems for root respiration and the uptake of nutrients.
Anaerobic decomposition produces acidity, which may cause toxic conditions around the roots
and prevent nutrient uptake. Bog plants have large intercellular spaces to facilitate the
movement of gases round the body. Many require less oxygen for their metabolism than do
comparable mesophytes. Leakage of oxygen from the roots may give local aerobic conditions
and may help to overcome the accumulation of toxins.
© Ian D. Rotherham 2015
(b) The problem of nutrient deficiency: Bogs are deficient in many plant nutrients because of
the acidity and the storage of nutrients in peat. Three main strategies have evolved in response
to this.
(i) Nutrient accumulation: Many bog plants, including the sphagnum species, are adapted to
grow under conditions of low nutrient supply. They can accumulate ions selectively from
dilute solutions and retain them until they are needed for growth.
(ii) Nitrogen fixation: Nitrate is particularly scarce in bogs. Several plants, including bog
myrtle, have root nodules containing symbiotic bacteria which enable them to fix atmospheric
nitrogen.
(iii) Carnivorous habit: Some plants supplement their nutrient supplies by catching and
digesting insects. British species of insectivorous or carnivorous plants include the sundews
(Drosera species) and the butterworts (Pinguicula species). Both of these have sticky leaves
that trap insects and then secrete enzymes to digest them.
BOG ECOSYSTEM FUNCTION.
(a) Productivity and food chains: Primary productivity is low compared with other
ecosystems. Only the tundra and hot deserts are less productive than sphagnum bogs. Most net
productivity is stored as the undecomposed organic matter of peat. Very little energy is
transferred through food chains.
The detrital food chain is limited by the anaerobic conditions. In the grazing food chain
invertebrates predominate, especially those species of insect, which require water for
reproduction. The invertebrates may form an important food supply for birds.
(b) Nutrient cycling: Decomposition is inhibited by acidity and the anaerobic conditions.
Cycling occurs slowly because of the accumulation of nutrients in peat. Available nutrients are
scarce although supplies may be augmented by inputs from precipitation and drainage from
adjacent areas. If the input from drainage is significant, the bog is rheotrophic, whereas if the
input is negligible the bog is ombrotrophic.