|
|
Home
>
2. Rationale
>
2.1 Selection
|
Previous
Next 
|
|
|
|
|
The objective of the
Review has been to select according to established criteria of
nature conservation value a series of sites which gives acceptable representation of
all the more important features within the range of variation in natural and semi-
natural ecosystems in Britain. The process of working towards this goal involves
three distinct stages, though the second two are so interwoven that they tend to be
thought of as one. These stages are as follows:
(i) Recording the intrinsic site features This is the
straightforward though
usually laborious identification and recording of the primary scientific data
for
the site, to describe its range of ecosystem variation in terms of environmental
and biological characteristics, which can be used to judge (ii).
(ii) Assessing comparative site quality
On the basis of the
scientific record obtained in (i), the quality of each site is
compared with that of other sites of similar type, so that there is a continual process
of selection to identify the ' best' site within a related group.
(iii) Choosing the national series of key sites
This involves decision
on which, how many and what extent of important sites should
constitute the national series, and is the most difficult part of the whole process to
rationalise satisfactorily, since it is essentially subjective, even when based on a
consensus view. These three phases will now be considered in detail.
Recording the intrinsic
site features
For a review of this
kind to be possible, there is a need for adequate knowledge of the
range of natural and semi-natural ecosystems in Britain, at least qualitatively, and
preferably quantitatively, in terms of habitat and associated organisms. The analytical
description and hierarchical classification of the whole range of ecosystems
represents a taxonomic framework which gives a basis for identifying and recording
the variety of features at any site, and enables one to compare different sites, discern
geographical trends and differences, and select sites according to properly defined
criteria. Ideally, one would wish to consider in this way all the components of an
ecosystem, including the inorganic factors, human influence, plants and animals. In
practice, such are the imperfections of our knowledge and capacity for descriptive
analysis that we have at present to limit our attention largely to the vegetational
component of the ecosystem. This is, by general consent, the most useful
parameter by which to characterise the ecosystem, for it is an integrated expression
of a complex of interacting environmental influences, and at the same time is the
major determinant of the animal component.
A hierarchical classification
of vegetation which uses environmental and life-form
criteria to separate the classes of higher rank is more useful for present purposes
than one which relies on purely floristic (i.e. phytosociological) criteria. Accordingly, a
primary separation has been made into the seven main ecosystem groups of
Coastlands; Woodlands; Lowland Grasslands, Heaths and Scrub; Open Waters;
Peatlands; Upland Grasslands and Heaths; and Artificial Ecosystems. These are
regarded as formations (= major habitat grouping or ecosystem type).
These are intergrading
or even overlapping classes, with arbitrary and artificial
boundaries drawn between them, and two or more of them may be represented
within the same site. Peatlands, for instance, are well represented within upland
grassland and heath sites. Nevertheless, this has proved to be a convenient and
practical subdivision into classes of first rank. Separation into classes of second and
third rank has been according
to life form and structure of the vegetation,
physiography, or edaphic criteria, as seemed most convenient. The ideal would be to
produce final classes of lowest rank determined essentially by floristic criteria
(vegetation or community types, noda, associations), but only for upland grasslands
and heaths are phyto-sociological data sufficient to allow this degree of definition.
The whole task has, in fact, been greatly handicapped by the lack of a standard
countrywide description and classification of British vegetation types. Dominant,
constant and characteristic plant species have been used to define the upland
vegetation types. Even at this finer level of analysis, there are few if any real
discontinuities in vegetational variation, and the limits between related vegetation
types are mostly arbitrarily drawn. For the formations other than the upland
grasslands and heaths, the description of vegetation has been more flexible,
according to present availability of knowledge.
The units of vegetational
classification of any rank may be used as the basis for
ecosystem recording on any site, but the lower the rank of unit employed, the more
detailed and accurate does the record become. In this vegetational taxonomy, the
units of 'nodum' (community type) rank, even if only provisional, may be regarded as
equivalent to species in classical taxonomy, i.e. they represent a concept of parallel
utility. The diagnosis of vegetation types thus gives a means of identifying plant
communities encountered subsequently in the field, and of recording these simply,
thereby providing a rapid but detailed description of the range of variation. It is,
however, essential to characterise ecosystems in terms of as many features as
possible, and supplementary information has been added, as available. Inventories of
plant species have been compiled for as many sites as possible; vascular plants and
bryophytes have been recorded most fully, lichens less so, whilst fungi and algae
have received uneven and inadequate study, and have often been omitted. Species
which are rare, local or decreasing are indicated in the lists, as are members of
important phyto- geographical elements.
The vegetation of open
waters poses considerable problems of description,
especially in terms of plant communities. Not only are there practical difficulties in
examining and recording submerged vegetation, but the communities of aquatic
plants are often open, heterogeneous and vertically stratified. Moreover, the algae,
especially planktonic forms, are such an important component of the aquatic
ecosystem that they must be considered as well, and the composition of the
invertebrate fauna has also been used as an important criterion in the description
and assessment of open water sites.
Apart from the open
waters, it has not usually been possible to record animal
communities as a parallel to vegetation types, and zoological records have consisted
mainly of species inventories, with some indications of population size for certain
vertebrates. Birds, mammals, reptiles and amphibia and freshwater fish have been
fairly well recorded for most of the important sites. Recording of terrestrial and some
aquatic invertebrates is still in a highly fragmentary and unsatisfactory state.
Macrolepidoptera and Odonata are the best known taxonomic groups, but even here
records are inadequate for many sites. Species lists for many groups of freshwater
invertebrates, together with a measure of abundance, are available for most of the
key open water sites. Specialist surveys of other invertebrate groups such as
Curculionoidea (Coleoptera) and Arachnida, have given detailed knowledge for a
limited number of sites, but patchy information of this kind is of mixed value, for it
may lead to the overlooking or under-rating of unsurveyed but important sites. As with
plants, efforts have been made to indicate occurrences of animal species which are
rare, local, declining or of geographical importance. Knowledge of habitat and
vegetation often makes it possible to predict the presence of characteristic animals
with fair accuracy, and the various sections on fauna in vol. i follow an ecologically
based treatment which indicates these relationships.
Climatic data of particular
ecological relevance have been noted, especially rainfall,
temperature and snow cover. The main geological and geomorphological features of
sites have been recorded, with emphasis on lithology and especially the available
lime content of the rock. Data on soil types and their chemical characteristics are
available for some sites, but pedological information is rather uneven. Analyses of
dissolved and particulate minerals are available for all open water sites. Biotic
influences, especially those involving man, have been assessed and described
whenever possible. Not only are past and present land use important because of
their effects on the stability and present composition of the ecosystem, but some
forms of land-use are also of intrinsic interest (e.g. coppice or water meadows).
Even completely artificial sites with strong biological interest have been included in
the survey. Detailed knowledge of the history of a site enhances its value, especially
for teaching and research, so that relevant historical records have been included with
site data whenever possible. The data for each defined area were entered on site
record cards or check sheets and species record cards, boundaries selected and
marked on a map, and an integrated statement prepared summarising the important
environmental and biological features of the site.
The term ' site' has
been used, for convenience, to refer to any surveyed area of
land, large or small, for which prescribed boundaries can be drawn on a map to
define a single geographical unit. There is a certain implication that these boundaries
are clearly recognisable and self-defined on the ground, but this is often far from the
case, especially in large continuous tracts of upland, where the limits to a site usually
have to be arbitrarily defined. The problem is discussed in greater detail on pp.
16—17. |
|
A number of different
criteria have, by general agreement and established practice,
become accepted as a means of judging the nature conservation value of a defined
area of land (= site); the following have been used in the Review.
Size (extent)
In the lowlands of
Britain where semi-natural habitats tend to be highly fragmented,
the importance of a site usually increases with size of area, and the concept of the
'viable unit' embodies the view that there is a minimum acceptable size for areas
which need to be safeguarded in order to maintain their conservation interest. With
woodlands or lowland grasslands and heaths, many of the best sites are undesirably
small in their total area. Larger sites are not always valued more highly than smaller
ones if other qualities are not equal, and minimum or optimum size for a key site
varies according to the type of formation. With upland grasslands and heaths, and
coastlands, the problem is often the converse one of having to restrict the choice to
an area of reasonable size, i.e. not too large. In practice, the extent of a key site is
determined by a variety of factors such as diversity, particular interest, and 'natural'
boundaries. Size can also be taken as a mark of quality in terms of area of an
especially interesting habitat or vegetation type within any formation, or of numbers
(i.e. population size) of species of plant or animal. With species populations, an
aggregation factor is often involved, notably with colonial animals in which a large
proportion of the total British population is located within a relatively small number of
sites, i.e. high density may be an important feature. A high proportion of a national, or
still more, a world population of a species is regarded as very important. In the case
of a wood, size can also refer to the actual stature of the trees, tall well-grown
specimens being preferable to the small or poorly grown.
Diversity
One of the most important
site attributes is variety in numbers of both communities
and species, which are usually closely related and in turn depend largely on diversity
of habitat. It is especially desirable to represent ranges of variation shown by
important ecological gradients, e.g. catenas, altitudinal zonation, fading influence of
salt spray and blown sand with distance from the sea, stages in pod-solisation of
soils, and effects of aspect on biological features. Site diversity is especially related
to differences in local climate and micro-climate, topography (affecting drainage,
exposure-shelter, aspect), parent rocks and derived soils. Variations in land-use and
management practice are often related to these primary factors and have further
important effects. Diversity is also related to extent, for the number of species of both
plant and animal shows a marked tendency to increase with size of area (the
species/area effect), quite apart from the probability that habitat variation will also
increase. Diversity is sometimes related to habitat instability and may then give
management problems. Often, instability or immaturity of habitat involves serai
change, and there is need to represent particularly striking examples of vegeta-tional
succession, though many of these inevitably require continual or repeated
intervention and management in order to preserve the early serai stages.
Sometimes, however, serai changes may have to be allowed to run their course, and
it is then important to ensure that earlier stages in the succession are represented
elsewhere in the area, i.e. the range of variation must not become depleted overall.
Conversely, diversity of an area can often be increased by appropriate management.
Areas containing high quality examples of more than one major formation, e.g.
woodland and peatland, have especially strong claims to key site status. Very many
sites rated as important mainly for one ecosystem contain lower grade examples of
another type which can be regarded as a 'bonus', giving enhanced value.
Richness of flora and
fauna, i.e. number of species, is an important criterion, and is
partly related to extent, but also depends greatly on environmental diversity. Species
diversity on areas of similar size is generally a reflection of habitat diversity. It is,
however, usual in Britain for an area of calcareous rocks and soil to support a much
richer flora than an otherwise similar area of non-calcareous substrata. Thus, areas
of limestone tend to be highly rated. Similarly, as the Bryophyta are as a whole a
moisture loving group of plants, they tend always to be better represented in the
more humid west of Britain than in the drier east. Many more species of bird are likely
to occur within a square kilometre of woodland than within a comparable area of
upland. In other words, species richness has to be treated as a factor of relative and
not absolute importance.
Naturalness
It has been customary
to use the term natural for vegetation or habitat which appears
to be unmodified by human influence. This is a rare condition in Britain, where so
much of the land surface has been profoundly altered from its original state by man's
activities. Tansley (1939) gave the name semi-natural to modified types of vegetation
in which the dominant and constant plant species are accepted natives to Britain,
and structure of the community conforms to the range of natural types. For instance,
many grasslands are semi-natural, whereas a hop-field or Sitka spruce plantation is
artificial. Roadside and railway verges have a semi-natural character in floristics, but
are regarded as artificial because of their linearity and setting. The distinction
between natural, semi-natural and artificial cannot be rigidly defined, and the
separations made in this review are somewhat arbitrary. Nature conservation interest
is affected by the actual degree of modification, in both structure and species
composition. An abundance or predominance of obviously introduced species
usually, in fact, reduces the value of an area, though in moderation, non-indigenous
species may add to diversity and interest.
This is a criterion
which rates differently according to the formation concerned. For
instance, unmodified vegetation is probably most consistently found in upland
grasslands and heaths and coastlands whereas the whole of the chalk grassland is
in some degree anthropogenic, and it is doubtful if any truly natural woodland
remains in this country. Some wetlands have been much disturbed through peat-
cutting or other activity, but natural processes of succession over a long period have
subsequently restored a nearly original character to the vegetation and habitat, e.g.
the Norfolk Broads. In general, this is a difficult criterion to apply: for one thing it is
often not easy to judge accurately the degree of modification (especially since the
nature of the truly natural ecosystem is often largely a matter of conjecture) and, for
another, the realistic view of conservation nowadays results in a high value being
placed upon some entirely artificial habitats. The bulk of ecosystems considered in
the Review is semi-natural, but insofar as they are identifiable at all, the types least
modified by man tend to be rated highly. Naturalness is perhaps of more concern to
botanists than zoologists. It is a condition which management sometimes seeks to
restore, and is often closely linked to rarity and fragility, i.e. its importance is partly
that of scarcity value and dwindling or threatened habitat.
Rarity
To many people, one
of the most important purposes of nature conservation is to
protect rare or local species and communities. Rarity on the national scale has been
given particular weight in the setting up of non-statutory ' species reserves' by bodies
such as the Royal Society for Protection of Birds and local Naturalists' Trusts. In the
present review, more emphasis has been given to the inclusion of rare communities,
habitats or groups of species, and individual rare species have tended to be regarded
as a bonus on sites selected for other reasons. The aggregation of several or many
rare species to form a group within a single site, as in a plant refugium, is regarded
as an important feature and has influenced the choice of certain key sites. Other
things being equal, however, the presence of even one rare species on a site gives it
higher value than another comparable site with no rarities.
The rare species which
have received particular attention in the present choice of
key sites are vascular plants, bryo-phytes, lichens, birds, mammals, Lepidoptera and
dragon-flies. Lack of knowledge or interest has led to the relative neglect of other
groups, though some consideration has been given to fish, weevils and spiders. A
recent examination of the status of rare British vascular plants (defined as species
known to occur now in not more than 15 lo-km grid squares of the Atlas of the British
Flora, 1962) has given a more objective means of assessing needs and
achievements in conserving this group (see Chapter n). Comparable data for other
groups are mostly lacking at present, but distribution mapping now in progress
should in time remedy the deficiency.
Some species tend to
be rare because they have extremely specialised habitat
requirements, others have become rare because they are the focus of some direct
human pressure, including collecting, or suffer indirectly by man's destruction of their
habitat. Rarity of species is often obviously related to rarity of habitat, which again
links with extent, but many rare species are relict, i.e. they have a discontinuous
distribution, with a great many absences from apparently suitable localities, resulting
from historical processes which have contracted and fragmented their range. A few
rare species are recent arrivals which have not had a chance to spread, and others
still (especially birds) are 'fringe' species which could apparently spread, but are at
the limits of their climatic
environment. Rare species and communities are often thus
of great ecological and biogeographical significance, and their conservation is
considered to be important. It is essential to understand as far as possible what
makes a species rare, since this can affect management needs.
Rarity of habitat and
community is closely connected with fragility, though it
sometimes depends on the chance occurrence of unusual environmental conditions,
singly or in combination, e.g. serpentine is an uncommon rock-type generally, whilst
limestone is comparatively rare at high elevations.
Fragility
This criterion is complex
but essentially it reflects the degree of sensitivity of habitats,
communities and species to environmental change, and so involves a combination of
intrinsic and extrinsic factors. Some ecosystems, such as certain serai vegetation
types and associated animals, are inevitably unstable and ephemeral, and may
require continuous management to maintain them in a desired state. Vegetational
climaxes tend to be more inherently stable, but the natural, climatic types are
necessarily more fragile than the biotic types. Intrinsic sensitivity to change varies
considerably according to the organisms involved, e.g. during climatic shift,
vegetation has a certain inertia of response, whereas certain insects may react very
rapidly. Different species within the same taxonomic group can also vary widely in
their resilience to adverse conditions.
Certain physical conditions
besides climate may give an extrinsic disposition towards
fragility, e.g. gravitational instability or a delicate balance in water table, but on the
whole it is imminence of human impact, representing 'threat', which forms the main
second element in this criterion. Virtually all natural and semi-natural habitats are
sensitive to human impact of one kind or another, but there are geographical
differences in vulnerability. Fragility rating for a particular ecosystem or site may also
increase as land-use pressures intensify and spread. For instance, the great blanket
bog ' flows' of east Sutherland and Caithness are easily damaged, but remain
relatively safe unless there is increased interest in exploiting these peatlands for fuel
or forestry. Some sites have escaped destruction largely by chance, e.g. certain
chalk grasslands which, though fairly stable under the traditional grazing
management regime, are extremely vulnerable to agro-economic trends. The nature
conservation value of many important sites is therefore largely dependent on
freedom from radical change in the established land-use pattern.
Fragility is thus a
dual concept, but in practice the different elements have usually to
be taken together. Fragile sites are usually highly valued, in that they so often
represent ecosystems which are highly fragmented, dwindling rapidly, difficult to
recreate, or perhaps threatened with total disappearance. Other criteria such as
rarity obviously tend to enter this evaluation of survival risks. There are, however,
cases where fragility is such that viability is also extremely doubtful, even under
favourable conditions of management.
Fragility also applies
to species of plant and animal, and especially includes relict or
fringe species which maintain a foothold under marginal or suboptimal conditions; it
is thus again linked with the criterion of rarity. A good example of a fragile species is
the reintroduced large copper butterfly at Woodwalton Fen, for this would clearly die
out rapidly but for careful management. Many of the rare British breeding birds, such
as red kite, avocet and marsh warbler, are essentially fragile species, in that a small
increase in adverse environmental pressure could easily tip the scales against their
chances of survival.
The most fragile ecosystems
and species have high value, but their conservation
may be difficult and often requires relatively large resources.
Typicalness
While key sites, especially
the 'living museum' kind, are usually chosen as the best
examples of particular ecosystems, their quality may be determined by features
which are in some degree unusual. This is valid but it is also necessary to represent
the typical and commonplace within a field of ecological variation, insofar as this
contains habitats, communities and species which occur extensively or commonly.
Sites sometimes have to be selected for their characteristic and common habitats,
communities and species, and it is then necessary to overlook the absence of
special or rare features. This criterion links particularly with research needs for
experimental areas, in which homogeneity may be a desirable feature, for a
sufficiently extensive stand of a particular vegetation type is sometimes required, e.g.
for plot replication is randomised treatments. The ordinary as well as the unusual
attributes sometimes both occur within the same site, and a great many sites rated
highly on other criteria take adequate account of typical and commonplace features.
By definition, unusual communities or ecosystems may have only a few available
samples, whereas there may be a much wider choice of those which are typical or
common, and the actual selection may have to be somewhat arbitrary, or influenced
by non-scientific factors.
Recorded history
The extent to which
a site has been used for scientific study and research is a factor
of some importance. The existence of a scientific record of long-standing adds
considerably to the value of a site, and can elevate its rating above that of a site
comparable in intrinsic quality, but about which little or nothing is known. For
instance, the importance of Wicken Fen, Cambridgeshire, is enhanced considerably
by the large body of biological and ecological data collected over several decades,
giving a picture of the processes which mould and change the nature of the
ecosystem in time. The detailed stratigraphical and pollen analytical studies made at
Cors Goch glan Teifi show a classical developmental sequence from lake to raised
mire and give this site an importance which could not be accorded simply from an
examination of its present surface features. In some cases, sites form the location of
long-term studies and experiments whose value would be seriously damaged or
destroyed if these study areas were no longer available.
This criterion should
not, however, be over-rated. It is less important than the intrinsic
features of the sites themselves, for in time the differences in amount of information
about sites will tend to disappear, though there may well remain differences in
historical value which are directly related to intrinsic site features (e.g. in the
completeness of a stratigraphic sequence). Recorded history has not therefore been
used as a criterion on its own, though there are instances, e.g. Kerloch Moor,
Kincardineshire, where it gives added value to a typical ecosystem, and may with
passage of time advance the claims of a site to key status. Where the research has
revealed classical features of the site, it points to an important intrinsic feature, but
research which is classical in the sense of revealing or extending ecological
principles can also give added value to an area.
Position in an ecological/geographical
unit
In the event of two
sites representing a certain formation being of equivalent intrinsic
value, contiguity of one site with a highly rated example of another formation is
regarded as conferring superior quality. Where practicable, and without lowering the
standards of selection, it has been felt desirable to include within a single
geographical area as many as possible of the important and characteristic
formations, communities and species of a district. Clearly, there are few areas
where anything approaching a comprehensive representation could be made, and
these are mainly in northern and upland districts, where fragmentation of semi-
natural habitats is least. Such areas as the New Forest, Hampshire; the Isle of
Rhum, Inverness-shire; Durness, Sutherland; Foinaven and Meall Horn, Sutherland;
Inver-polly and Knockan, Ross-Sutherland; and Cairngorms, Inverness-shire,
Banffshire, Aberdeenshire, illustrate the point. This criterion is obviously related to
those of size and diversity. There is also a practical convenience in having two
different key sites within a single geographical area.
Potential value
Certain sites could,
through appropriate management or even natural change,
eventually develop a nature conservation interest substantially greater than that
obtaining at present. Sometimes a site once known to be of exceptional quality has
deteriorated seriously in recent years through adverse treatment. This is especially
true of certain woodlands which were spoiled by war-time timber extraction, and of
some mires which have dried out through burning and/or draining. In such cases, it is
sometimes probable that in time, and with suitable management - which depends
partly on availability of adequate resources - the former quality of the ecosystem can
be restored. When other high-quality examples of the ecosystems concerned cannot
be found to take the place of those which have deteriorated, there is good reason for
choosing the latter as key sites in the hope that restoration can be achieved through
appropriate management. The potentiality for regeneration of high quality mire
ecosystems in peat workings is shown by the Norfolk Broads and Moorthwaite Moss,
Cumberland, and it is hoped that the interest of Shapwick Heath, Somerset, and
Thorne Waste, Yorkshire, will recover in some degree.
Similarly, when a particular
ecosystem has been lost altogether, or when no viable
examples remain, it may be best to attempt to re-create an example de novo, starting
either from some quite different kind of formation, or from one with a closer
relationship to that desired. As an instance, it would be possible to produce a
woodland of desired type from a grassland or an area of scrub. If, as has been
suggested, projected estuarine barrage schemes make provision for the
development of completely new freshwater and other wildlife areas, it may be that
sites of high quality will come to exist in places where conservation interest is at
present quite different or merely negligible. Artificial reservoirs and flooded gravel
workings are numbered among the high-quality open water sites, and the importance
of other artificial habitats is an indication of the possibilities for creating sites of nature
conservation interest. In many instances it would be advantageous to link potential
value with the previous criterion, and to choose land contiguous with or part of a key
site selected for its existing values.
Intrinsic appeal
There is finally the
awkward philosophical point that different kinds of organism do not
rate equally in value because of bias in human interest, as regards numbers of
people concerned. There is no disputing that, for instance, birds as a group attract a
great deal more interest in the public generally than do spiders or beetles. Similarly,
colourful wild flowers and rare orchids arouse more enthusiasm than toadstools or
minute liverworts. While science may view all creatures as equal, therefore,
pragmatism dictates that in nature conservation it is realistic to give more weight to
some groups than others. This view is supported by the fact that knowledge of the
distribution and numbers of the 'popular' groups is often much greater than for
obscure groups. The Review has thus given a good deal of weight to ornithological
interest (apart from pest species such as the woodpigeon) and many wetlands and
coastal sites have been rated highly for their concentrations of wildfowl, waders and
seabirds. Nevertheless, within the limitations of available knowledge, an attempt has
been made to ensure that the less popular groups of organisms are adequately
represented in the key site series. |
|
These criteria tend
in some instances to merge or even overlap with each other, and
they often run parallel and so are additive; but sometimes there is mutual
incompatibility, e.g. rarity is seldom compatible with typicalness or diversity with
homogeneity, and while naturalness is usually rated highly, the Norfolk Broads are
artificial in origin yet must be regarded as one of the most important wetland areas in
Britain. The application of these criteria in site assessment is a complex matter,
difficult to rationalise or explain simply. In general, for the first five, the larger the
score the higher the quality. Large size does not necessarily confer high quality if
there are no other desirable features, but does so in combination with other attributes
such as marked diversity or presence of rare communities/species. Conversely,
marked diversity may not rate highly if the area involved is too small. However, a rare
and fragile type of ecosystem can be extremely important, even if it is small and fairly
uniform. Site assessment often involves variable weighting of criteria, i.e. they are not
all of equal importance, nor everywhere of the same relative importance. Some
criteria cannot be used on their own, and while some are independent others are
inter-dependent. Ideally, to qualify as a key site, an area should rate highly according
to as many criteria as possible, but few sites rate highly in all qualities; while a
majority of key sites have been selected for a high quality conferred by a combination
of features, some have been chosen for a single important attribute. Much depends
on the choice available within any major ecosystem or community type.
The best way of discussing
these criteria and their application is to take a specific
example of a site which has long been accepted as a classic area of wildlife and
habitat in Britain, and to analyse why it is so highly valued.
The North Norfolk Coast
is a maritime ecosystem complex containing extensive
examples of sand dunes, salt and brackish marshes, shingle beaches and inter-tidal
flats, largely unmodified by man. The physical and biological processes involved in
shore accretion and erosion are especially well demonstrated, and classical studies
have been made of the dynamics of coastal physiography and plant succession, and
of the relationships between the different habitats and their vegetation. The vegetation
is rich in species, and there are especially large populations and extensive
communities of certain plants which are characteristic of salt marshes in this part of
Britain: a number of rare species occur, including some at the limits of their British
range. This coast is an important breeding ground for certain coastal and brackish
marsh birds which include big populations and interesting communities of rare
species. In the autumn and winter, it is a major haunt of passage and wintering birds,
especially waders and wildfowl. The invertebrate fauna is large and includes many
rare species. Some of these features, such as the colonially breeding terns and the
sheets of sea- lavender in flower are sufficiently spectacular to excite the lay public
and the whole area serves an important educational function over a wide range and
level of interest.
The aspects of importance
are clearly inter-related, but there is an over-riding
aspect, the total diversity of the area, which gives it an especially high value. This
includes not only the diversity in range of major coastal features but also in species-
richness of certain communities. The extent of the area and particular communities,
the size of the populations of certain species, and the presence of many rare
species are notable features. The natural state of the whole ecosystem is unusual
and the range of variation also encompasses that characteristic of such coastal
formations in this part of Britain, so that it may also be regarded as representing
typical features. The research and educational value of the area is very high and the
degree of documentation of many features of scientific interest over a long period
gives an additional measure of importance. The physiographic interest of this coast
is a further factor, although this aspect of nature conservation is not specifically
considered in the present review.
These attributes of
the North Norfolk Coast thus provide standards against which
examples of similar ecosystems can be judged, and the kinds of values involved can
be applied more widely to the assessment of other types of ecosystem. To continue
the discussion in more general terms, similar sites are compared to see which
scores most highly for particular features or combinations of features, the aim being
to produce a final evaluation of the overall quality of each in relation to standards for
its type, i.e. position in the abstract ecological classification. The judgements involved
are comparative and therefore relative, and they concern what is available, which
often falls well short of the ideal. The varying use and emphasis of different criteria
according to formation are discussed under the accounts of the formations
themselves.
The comparative assessment
of sites could in theory be made more objective by
applying a scoring system to the above criteria, so that the total score for a site
would be a measure of its overall quality. While it was found possible to apply this
procedure locally, or within a limited range of habitat (it was done in Coastlands) no
attempt was made to develop a comprehensive scoring system to cover the whole
range of British ecosystems. Not only are there complexities difficult to deal with,
such as the frequent lack of independence of criteria, and the varying absolute and
relative values of different criteria according to requirements, ecosystem group and
locality, but basic information for different formations and sites is so variable at
present that a scoring system could not be evenly applied throughout the country.
Nor is there a satisfactory logical basis for allocating actual score values to different
site features. While these problems may eventually be solved by careful study of
conceptual difficulties and intensive collection of field data, at the moment any such
attempt to quantify the process of selection for all key sites could only give a spurious
objectivity. It is nevertheless sensible to follow a limited quantitative approach when
this is feasible and valid as for example, by counting the number of communities or
species in assessing such features as diversity. Recent studies, such as that by
Helliwell (1973) indicate the kind of advances in approach which may lead to a more
consistent and satisfactory methodology of evaluation of nature conservation interest.
Choosing the national
series of key sites
So far, discussion
has been limited to the processes whereby the respective merits
of two or more sites of basically similar character are compared and the sites then
arranged in order of relative importance. There remains the more difficult task of
choosing a series of the most highly valued sites which will form an acceptable
sample of the national range of variation in natural and semi-natural ecosystems.
Part of the problem
may be approached reasonably objectively; given time and
resources, the field of variation can be charted and samples (reference points)
identified and described. The more intractable difficulty lies in the interpretation of the
word 'acceptable' - for this interpretation must necessarily be subjective, since the
ultimate purpose to be served is so broad and varied that no simple definition is
possible, and it cannot be related to any absolute standards.
There is some analogy
with the methods of taxonomy, for the taxonomic categories
that are used to describe the field of ecosystem variation are also the abstract units
on which the selection of a series of key sites is based. For instance, having grouped
peatlands into six major classes of mire, it is a natural consequence to select key
sites which will represent each class. And since each major class of mire is divided
into a range of subclasses according to variations in climate, topography, hydrology
and floristics, it follows that each of these subclasses should be represented in the
series of key sites. The difficulty lies not in choosing between mire sites which are
obviously different in major features but in deciding how many to choose from a
number of mire sites which belong to the same major class but differ from each
other in more minor features. This is reminiscent of the basic taxonomic problem of
deciding on the spacing of the reference points within a field of continuous variation-
should they be closer together or farther apart? At one extreme one could select
virtually all sites with semi-natural or natural ecosystems, so that no possible minor
variant could be omitted, while at the other extreme one could select so few sites that
a great deal of the field of ecological variation was left out of the series. Clearly,
something approaching the 'happy mean' is needed - but how does one strike the
best point of balance ?
The series of key sites
to be presented represents the point of balance in the
collective judgement of a number of people, just as an accepted taxonomic system
tends to lie somewhere between the views of the 'splitters' and the 'lumpers'. A
second major conceptual difficulty arising here is that there is not one basis but
many for a taxonomy of ecosystems. There is general agreement that vegetation
provides the best basis for such a system, but even vegetation may be looked at in
different ways. For instance, woodland may be classified according to species-
dominance within the tree layer, floristics of the subordinate layers, physical habitat
factors (climate, topography, soil) or management/ structural type. Often, these
different parameters can be applied at different hierarchical levels within a single
classification, and when this is both possible and convenient it seems a sensible
practice to follow. These are different aspects of ecological diversity and, while they
often show a degree of parallelism, each has claims to be considered separately
when the choice of representative sites for the particular range of ecosystem
variation is made. One is thus faced with further questions, namely, which and how
many specific bases of ecosystem taxonomy shall be considered in selecting a
series of key sites, and in what order of priority ?
The actual selection
of a national series of key sites covering all natural and semi-
natural ecosystems is in abstract a complex procedure, entailing in the choice of
each site the appraisal of a body of recorded information and the application of
various criteria for assessment in such a way that they become integrated as
judgement is made. The description of the thought processes involved is a lengthy
business, entailing various rationalisations and discussion of abstract concepts. Yet
in reality, the procedure of site assessment and selection includes a number of steps
which are taken almost automatically, in the same way that a person crossing a busy
street makes numerous observations and calculations about his own motion and that
of vehicles, without ever thinking consciously about the matter. Moreover, in
analysing retrospectively the processes involved it is easy to claim a degree of logic
and a sequential order of events which were not followed in practice. For instance,
the comparative assessment of sites and determination of acceptable representation
are not really separated in the manner indicated in this written presentation, but
proceed together pari-passu as survey progresses and knowledge accumulates.
And to a considerable degree, the criteria discussed under comparative assessment
are also involved in the election of a site to the national series; when the application
of these criteria indicates that a site is quite exceptional or unique, its selection
automatically follows.
The position at the
beginning of the present review was somewhat as follows. Over
100 NNRs representing the six major formations and various subdivisions of these
were already declared. It is impressive that the original assessment of the great
majority of sites proposed as NNRs in Cmd 7122 remains unchanged in the present
review. It is, indeed, remarkable how consistently unanimous a view is to be found
amongst experienced field ecologists and naturalists about the outstanding merits of
many key sites. To the uninitiated it may seem that the manner of judgement is an art
rather than a science but, whatever the case, the standards show a considerable
degree of uniformity. The need for the Review grew not from any feeling that the
established standards required re-judging, but from an increasing awareness that if
these standards were to be applied consistently through the full range of ecosystems
in Britain, a considerable number of other sites had equally strong claims for addition
to the list of key areas. In other words, as knowledge of the range of ecosystems in
this country increased, it became clear that there were many gaps in representation
of important types. In some instances it was obvious that sites which had newly
come to light were decidedly more valuable than certain others well known and
already safeguarded.
People do not, in fact,
usually go around thinking that this or that particular abstract
type of ecosystem requires representation, but with the knowledge that, for example,
A, B and C are outstandingly good upland sites of different kinds, but that there are
other sites of unknown value which need examination. If upland site D is then found
and looks good, the first question to be answered is whether it is broadly similar to or
different from A, B or C. If D is similar to one of the others, a decision is needed as to
whether it is inferior or superior, and this depends on evaluation of detailed
differences. If D is markedly inferior it is dropped from further consideration as a key
site, but if it is only just inferior, it may be included as an alternative to the other.
Should D be superior to any other similar key site, it will automatically be included in
the national series, and its rival will either be dropped or retained as an alternative.
On the other hand, if D is quite different in main features from any other key site, one
then has to judge whether it is sufficiently important in its new features to justify
representation in the national series as a further type of upland. There is a continual
and cumulative process of comparison and selection or rejection based on serial
observations of a number of sites. It follows that those sites which one encounters
first will tend to become standards, and this can be a source of bias. This kind of
bias tends to diminish as experience of number and variety of sites grows.
The process is complex
in practice and depends at the outset on a sufficiently wide
knowledge of the detailed character and range of national variation in natural and
semi- natural ecosystems - in short, an adequate field experience of vegetation and
wild animals. This basic expertise naturally increases as survey progresses. The
more there is background knowledge and experience on which to base the
judgements involved in site selection, the more reliable and useful the process is
likely to be. The pitfalls are sometimes unexpected. For instance, it might be thought
that there are pedological and ecological grounds for representing all the major
geological formations in the series of upland key sites. Only field experience can
teach that the difference between, say, the Ordovician and Silurian formations per se
is usually ecologically meaningless, and that it is far more important to differentiate
between the calcareous and non-calcareous rocks within each of these formations.
While particular needs
will be discussed under each major formation, the following
general requirements for achieving the declared objective of the Review may be
stated:
Selection of a series
of sites adequately representing the national range of variation
in the following ecological features:
Climatic
Biological features dependent on local and regional gradients
of climate. Local
gradients of climate are related especially to such topographical factors as
altitude, aspect and proximity to water bodies; whereas regional gradients are
concerned with larger scale tendencies such as the increase in oceanicity
with distance west and decrease in mean temperature with distance north.
Physiographic
Biological features associated with major variations in land
forms. Most
diversity within this class may also be analysed in terms of climatic or edaphic
variation, but it is often useful to consider physiography as an ecological factor
in its own right. „ ,
Edaphic
Biological features associated with major variations in physical
and chemical
properties of soils and their parent materials, i.e. geological formations.
Physical soil factors include especially wetness (determined by soil porosity,
angle of slope, configuration of ground, water supply and evapotranspiration),
while chemical factors include especially acidity-alkalinity (pH) and availability
of important nutrients, notably calcium, potassium, nitrogen and phosphorus.
There is a need to represent the complete range of soil types (identified in
terms of physical/chemical profile characteristics) associated with the whole
range of natural and semi-natural plant communities. Soil conservation is
usually understood as concerned with maintenance of fertility and carrying
capacity, and, while this may be an important requirement on some, it is not
the case for every key site, and sometimes there is a need to prevent nutrient
levels from increasing. The motives for soil management are different in
nature conservation from those in agriculture.
Anthropogenic
Biological features associated with major variations in system
of land
management by man. These mostly represent varying degrees of modification
of natural ecosystems by human influence, including clearing of woodland and
scrub, burning, grazing and ploughing; they also include managed types of
semi- natural ecosystems within woodland, grassland, heathland, upland,
wetland and some coastland.
Some artificial ecosystems may have considerable conservation
value, but it
is usually felt that on their own these have no strong claims to representation
in the national series of key areas, as in the case of plantations of alien
conifers such as Sitka spruce. Sometimes an artificial habitat eventually
develops a semi- natural character and may then have stronger claims to be
considered in the selection of key sites, e.g. reservoirs, disused gravel pits
and quarries. Other essentially artificial habitats which develop a semi-natural
character may, from their very nature, be unsuitable for consideration as
conservation sites on the national scale, e.g. hedges, roadside verges and
railway embankments, yet they may have strong claims at the local level.
The biological features
alluded to above include both communities and species of
plants and animals. Ideally, at least one good example of every described plant
community in Britain, and one viable population of every wild plant and animal
species should be represented within at least one grade i or 2 site. It must at once be
stated that achievement falls well short of this ideal. For one thing, vegetational
taxonomy based on phytosociology is incomplete and many plant communities are
not yet identified, while the description of animal communities has hardly begun and
animal species are so numerous that the problem of their representation cannot
possibly be tackled satisfactorily at the species level. Moreover, neither communities
nor species are all of equal importance, but their varying value (and hence claims for
representation) cannot yet be properly quantified.
At the risk of being
repetitive, it is necessary to stress again that adequate
representation is not synonymous with uniform or total representation of the field of
variation. It is not the intention of the Review to advocate the safeguarding of every
minor variant of habitat or community, especially when these are isolated from more
important areas. The main need is to ensure that all major types are represented,
and that all the really important sites are included. Sometimes, the philosophy of ' as
large a sample as possible' has been applied to certain fragile and/or rare habitats,
communities and species, especially when their international importance is high.
This is especially the case with the major concentrations of wintering wildfowl and
waders, and colonial breeding coastal birds, for which Britain has a strong
international responsibility in conservation; virtually all the areas with numbers of
these birds above certain levels have been included as key sites, though not all are
grade I. Every effort has been made to avoid extravagance in the compilation of the
national series, and the final list of grade I and 2 sites is regarded as a reasonable
minimum.
The choice of ordinary
sites has been judiciously limited, and whilst the Review has
taken some account of research needs, it has done so to a varying degree. Many of
the key sites chosen have a known research value, which has been regarded as a
significant attribute (see Recorded history, p. 9). Virtually all key sites have a potential
research value, and the series as a whole would give a great deal of scope for
research, but there has been no attempt to choose sites for a specialist research
interest involving experimentation. Some sites with ordinary ecosystems which have
been the location of long-term and intensive research projects may assume an
increasing historical importance, e.g. Meathop Wood, Lancashire, for International
Biological Programme studies and Kerloch Moor, Kincardineshire, for red grouse
research. However, experimental research often places a premium on such
attributes as uniformity (for work involving sampling and replication) and accessibility,
and may involve considerable disturbance to the ecosystem, such as felling of trees
or deliberate removal of species. Since these criteria and activities are usually
difficult to reconcile with those discussed previously, it has been felt that the needs
for research sites primarily of the experimental type should be dealt with as they
arise, for they are often highly specific and relatively short term, as well as ad hoc
and unpredictable. No attempt has therefore been made in the Review to cope with
them, or to foresee all future research requirements relating to semi-natural and
natural ecosystems.
Similar considerations
apply to educational sites. For teaching purposes,
convenience of access is often an important criterion, and these activities may
create degrees of damage unacceptable within a classic 'living museum' site, e.g.
through disturbance of rare and sensitive nesting birds or trampling of fragile plant
communities. Many of these educational needs can be better met by sites of grade 3-
4 or lesser importance, though features associated with diversity make many key
sites especially valuable for teaching ecology, and sites showing various classical
features are
obviously the best demonstration areas for the phenomena in question.
All sites are thus regarded as having potential educational value, but the degree to
which this can be exploited will depend on various constraints, including both the
requirements for management and the conditions of ownership.
Sites can be important
in acting as reservoirs for species, including the genetic
diversity of these. The general principle of selecting sites which include a range of
phenotypic diversity in common and widespread organisms is likely to cater for many
requirements for living material which may arise, ranging from the need for
genotypically variable populations of species to parent stock for propagation work of
various kinds. The degree to which key sites will serve as reservoirs for the natural
dispersal of species must inevitably be variable and extremely difficult to assess, but
the potential is probably considerable.
Conclusions
The comparative assessment
of sites within a related group has been shown to
present conceptual difficulties in regard to the relative weight that should be attached
to the various intrinsic site features and to the different criteria which are applied in
evaluating these features. The selection of key sites to give an adequate national
series presents: a still more difficult test of reason. There are problems in achieving
consistency in choice of sites to form a series within a single formation type, e.g.
woodlands, but it is still harder to prescribe the emphasis required in selecting one
series of sites compared with another, e.g. a woodland series as compared with a
coastal series. Similarly, how does one decide what weight to place on the
representation of botanical and zoological features in relation to each other ? What
proportion of sites chosen should be of the classical and rare or typical and common
types ? How much prominence should be given to representation of rare species or
groups of species ? Should the disparity in total area between major formations
influence the numbers of key sites chosen to represent these ? For example, the
combined area of upland key sites is far greater than the total area of chalk grassland
remaining in Britain; should one therefore select a larger number of chalk sites to
compensate for the larger area of upland sites ?
There arise many questions
which cannot be answered with any precision or
according to clear-cut rules. The problems involved are a matter for careful thought
and considered judgement, having regard to the need for a fair balance between the
claims of the numerous and sometimes conflicting requirements involved in the
assessment and selection of sites. It is possible to find a consensus of opinion on
these matters amongst informed people working in this field who between them bring
to bear an enormous body of knowledge, experience and wisdom. This consensus of
view has repeatedly been sought, but the need for an adjudicator in cases of
disagreement was realised and one of the functions of the Scientific Assessor (see
p. 16) has been to resolve such difficulties by a personal and often arbitrary decision.
In time, it may be
possible to use more advanced techniques to achieve greater
objectivity and consistency throughout in the selection of a national series of key
sites. At present, the essential scientific data on which computer analysis is based
are far too inadequate for such a treatment to give more than a biassed and
provisional result, which could be misleading. Moreover, some aspects of the whole
process of assessment and selection are not yet measurable. In the meantime,
therefore, we have to rely on the computing and integrating abilities of the human
mind, whatever the shortcomings in this procedure may be. Since the purpose of the
Review is ultimately to satisfy a spectrum of human interests and activities, and is
therefore heavily dependent on a series of value judgements, it is, in any case,
difficult to see how this process can ever become completely objective. Some
obvious forms of bias have to be eliminated as far as possible, as in the case of local
or regional patriotisms, and personal preferences for certain criteria or features.
However, it remains true that many of the judgements made are still subjective even
when they are collective, and this is particularly so in deciding when the national
series of sites is adequate. There is, in fact, no final way of answering this last kind of
question, for it depends on values and factors which cannot be quantified on any
satisfactory basis. In the last analysis, the inclusion or rejection of a site in the
national series is based on informed opinion, and is thus open to argument and
alteration. Values are also prone to change in time, and future generations may look
at things rather differently. The present review is an attempt to prescribe the
contemporaneous requirement for conservation of special sites according to current
values, views, information and constraints. However elaborate the rationalisations
which might be made to justify the way it has been done, it would be wrong to
disclaim the element of intuition involved, though one hopes that this is built on
awareness and experience.
The methods of evaluation
and site selection used in the Review are therefore
provisional and pragmatic, and dictated especially by incompleteness of survey
information and the need to produce a working report within a reasonable time.
Urgency and realism rather than theory and idealism have been the keynote of the
operation. The issues involved are complex, and discussion is not made easier by
the semantic confusion which has arisen over a long period through the habitually
loose use of terms in ecology and nature conservation; these terms themselves now
have such breadth of application that they are often virtually meaningless, and require
further qualification. Within these limitations, an attempt has been made to explain
the thinking behind the Review, and the guidelines which have been developed in
relation to the situation in Britain. The results cannot be validated by reference to any
absolute standards or economic base, but must be judged more broadly in terms of
their eventual long-term contribution to nature conservation. |
|
|
|
|
|
