Climatically, edaphically
and topographically, the southern and eastern lowlands of
Britain, i.e. mainly England, is the region most suited to arable farming and human
settlement, and it is this part of the country in which the original ecosystems have
been most profoundly modified. Virtually all 'natural' habitat, unaffected by man, has
gone and relatively little of even a semi-natural character remains. Woodland is still
the major semi-natural habitat in the lowlands and its remnants from the main period
of clearance were, until very recently, composed largely of native species, managed
and cropped for their economic importance. Much forest land was also traditionally
kept as sporting preserve, rather than for the value of its timber, and the creation of
royal hunting reservations or chases has been instrumental in preserving large areas
of forest land. The open park woodland associated with large country houses has
also provided a particular type of wooded habitat which is largely confined to Britain.
During the last few decades, a waning demand for slow-growing hardwoods, and an
increasing need to manage all woodlands for an economic return, have contributed
to the accelerating replacement of native tree species by alien conifers. These new
woodland dominants profoundly alter the ecosystem in its subsidiary components,
notably the field communities and dependent animals, and usually create a much
impoverished type.
The sophistication
of modern agricultural practice is leading to the steady eradication
in arable areas of all habitats and higher forms of life extraneous to the crop itself, i.e.
the destruction of hedges and hedgerow trees, elimination of weeds and filling-in of
ponds. In some of the lowlands, large areas have been kept under permanent
grassland as pasturage for domestic animals, especially cattle and sheep. While
these are communities produced by man, some of the grasslands, especially on the
Chalk, are long established ecosystems of considerable biological richness and
value in their own right. Here, again, the last three decades have seen great inroads
into the remaining area of semi-natural habitat. Many of the permanent pastures have
been ploughed and converted to arable crops; even where they are retained as
grassland there has often been fertilising and re-seeding, which has completely
changed a botanical composition developed over centuries. Often, the only pastures
to escape destruction or modification have been on ground too steep to plough,
though with modern implements even steepness of slope is no longer such a
limitation.
In the lowlands, areas
of acidic sand and gravel have been sufficiently infertile to
discourage attempts at farming, and so have tended to retain semi-natural acidic
grassland, scrub and heath, notably with heather, bracken and gorse. Often this
semi- natural complex, probably derived from original woodland, is associated also
with common rights or maintenance of game preserves. Major areas of this kind
occur in south-east England in a discontinuous belt from East Anglia to the New
Forest and Isle of Purbeck. The area of such habitats has, however, contracted
greatly since 1945, for the application of modern agricultural techniques can convert
these types to farmland of reasonable productivity.
Rivers and streams
are well represented all over Britain. Those of the uplands tend
to be the eroding type, with swift-flowing turbulent and often rocky courses, whilst
those of the lowlands are mainly the 'depositing' type, slower-moving through alluvial
lands built up by their sediment over the ages. Upland open waters are also
predominantly oligotrophic whereas many of those in the lowlands are eutrophic.
The major lake-forming
processes in Britain were those of glacial erosion, and the
mountain regions of north Wales, the Lake District, Galloway and the Scottish
Highlands have large numbers of lakes and tarns. In the lowlands, glacial deposition
was dominant and consequently fewer natural lakes were formed. South of the area
covered by the ice at its maximum extent, natural bodies of standing water are
scarce indeed. Because of the local scarcity of natural standing waters in the south,
artificial lakes which have achieved a degree of naturalness (in certain cases, this
can be a relatively rapid process) such as some gravel pits, reservoirs, ponds and
especially the mediaeval peat diggings which form the Norfolk Broads are of
considerable biological interest. Open waters, particularly rivers, in lowland areas are
vulnerable to forms of disturbance not encountered in other habitats. Many lakes in
lowland Britain have in recent years been receiving increasing amounts of nutrients
from sewage effluents and from agricultural land and these have led to a number of
adverse biological changes, especially in depletion of flora. Most lowland rivers are to
some extent modified by the construction of artificial barriers and channels, and the
abstraction of water, which affect the rates of flow and alter the natural substrate, or
by the discharge of effluents including hot water, suspended solids, pesticides and
other industrial toxins, domestic sewage and detergents.
Many of these forms
of modification originate at points within the catchment remote
from the scientifically important tracts of river or lake, and activities such as
afforestation (involving extensive ploughing and fertilising), land improvement (also
involving fertilising) and mining (with discharge of waste material) in hill areas can
affect upland rivers markedly. On the whole modification is less severe in upland
than lowland areas, but oligotrophic waters are intrinsically more fragile than
eutrophic waters, and many of the finest oligotrophic lakes have been ruined by
conversion to water supply and hydro-electric reservoirs. The proposed large-scale
movement of water between catchments offers a new threat to the integrity of open
waters. There is also a heavy and increasing pressure on open waters for
recreational use, which can cause serious disturbance to marginal and submerged
plant communities as well as to wildfowl.
Permanently wet ground
with a vegetation cover (peat-land) was formerly much
more widespread in the lowlands, but has been greatly reduced in extent by drainage
and conversion to farmland. The most notable examples are the Fenlands of
Huntingdonshire and Cambridgeshire where the original expanse of swampland is
now represented only by a few island remnants, maintained with difficulty in a
somewhat modified state. Some ground has been difficult to drain, and locally there
is deliberate maintenance of high water tables, as in water meadows. Shallow lakes
and slow- flowing rivers often have a marginal fringe of swamp vegetation but, in
general, there appears to be a tendency for drying out of such habitats, through
falling water tables and hydroseral development, and many are progressing to carr
woodland or wet meadow. The local areas of raised mire, developed on plains where
the peat has been able to grow above the influence of mineral-rich water, are nearly
all modified from their original condition and show varying degrees of drying out, with
loss of Sphagnum cover. This kind of peat is valued as a source of moss litter and
many of the deposits are being worked extensively; afforestation or reclamation for
agriculture may then totally eradicate the original ecosystem.
In the north and west
of Britain, the cool, cloudy and humid climate is physiologically
unsuitable for many arable crop plants. Moreover, there is a prevalence of infertile,
acidic soils which can be raised to a reasonable level of productivity only by
considerable expense, and much of the ground is too steep, rocky or inaccessible to
be cultivated. Arable farming is confined to the rather limited areas of fertile lowland
on the plains adjoining the hills or in the upland valleys. The uplands themselves are
used mainly as pasturage for herbivores, notably sheep, grouse and (mainly in
Scotland) red deer. Cattle were formerly kept in much larger numbers than at
present, and many areas once had considerable herds of goats. Pasturage for these
animals was obtained by extensive clearance of the forests which formerly covered
the uplands to varying altitude, depending on local and regional differences in climate,
so that woodlands in the hill country are now fragmented remnants, modified by
recent management and frequently by grazing of the field layer. Within the potential
tree limit, British uplands are thus covered mainly by mixtures of derived grasslands
and dwarf- shrub heaths (especially Calluna heath), subject to heavy grazing and
repeated burning. Grassland predominates in the west and on the more basic soils,
and heather moor in the east and on the more acidic soils.
While the differences
between typical lowlands and typical uplands are fairly obvious,
the dividing line between the two is extremely difficult to draw in general. As lowland-
upland transition is recognised within most of the main formations, i.e. woodlands,
grasslands and heaths, peat-lands and open waters, and in the case of the
grasslands and heaths it is made the basis of a separation into two different
formations, the upland one representing the distinctive range of mountain
communities. There are floral and faunal differences between lowland and upland
zones, but they seldom, if ever, give a clear-cut boundary and there is usually a
gradual transition from one to the other. In many hill areas, the upper limits of
enclosed land give a useful, practical, though man- made boundary for delineating
upland sites and habitats. This criterion has the advantage of being ecologically
based, for it varies altitudinally according to regional differences in climate as do the
natural vegetation zones - a feature which makes it impossible to define any one
altitudinal boundary between lowland and upland. Nevertheless, this land-use
separation is not always valid for, in the more southerly British hills, vegetation
referable in floristics to lowland grassland and heath or peatland often lies above the
limits of enclosed land, and grades into more distinctly upland communities only at
higher levels.
Woodlands obviously
belong mainly to the lowland zone, and the upper edge of a
wood is sometimes used to define the boundary of an upland site. However, apart
from the fact that woodland is usually patchy on lower hill slopes, with very variable
upper limits, and often absent altogether, this formation is itself often separable into
distinctive upland types at higher levels and/or in northern localities. In many hill
areas, grassland, heath and peatland of upland type extends to well below the actual
tree limit. The potential tree limit (which varies from over 610 m to near sea-level,
according to geographical position) is regarded as the boundary between 'montane'
(higher) and 'submontane' (lower) zones. The lower limits of the submontane zone
correspond to the boundary between lowland and upland.
The submontane grassland
and heath complex covers great areas of the British
uplands, but on wetter ground grades into blanket mire, an acidic peat-forming
ecosystem in which the vegetation receives nutrients largely from the atmosphere.
Blanket mires cover large expanses of gently contoured land, even down to near sea-
level, in districts of high precipitation/evaporation ratio, and are especially associated
with the cool oceanic climate of northern and western Britain. They are variably
modified by human influence and show all degrees of drying out and erosion, though
some undisturbed areas remain. Though blanket mire was formerly too wet for tree
growth, it has in recent years been extensively converted by draining and planting into
coniferous forest, as have many areas of deforested
grassland and heather
moor. Large tracts of treeless upland up to 360-490 m have
thus been given a forest cover but the plantations are largely of non-native
softwoods, especially Sitka spruce and lodgepole pine.
The montane zone, restricted
to the higher mountains and especially extensive in
Scotland, contains a range of dwarf-shrub heaths, grasslands, peatlands, moss and
lichen heaths and rock communities, which as a whole probably show a closer
approach to natural climax vegetation than any other ecosystem in Britain now. Even
these, however, have been modified, mainly by reduction of woody species and
herbs, where grazing has been heavy and long established. Recreational
developments, notably skiing, hill walking and rock climbing, have in recent years
become a factor of some importance locally in mountain districts, and create their
own kinds of disturbance to habitat and wildlife.
Coastal land also contains
a good deal of habitat in a relatively undisturbed and
original state. This is especially true of sea cliffs, which occupy a good deal of the
British coast, but applies also to many sand-dune systems and shingle beaches.
Stable dunes and machair have been long exploited as grazing or even arable land,
and the higher, least sea-swept areas of salt marsh are used as pasturage, and
former saltings behind sea walls are now being extensively converted to arable land.
Coastlands are mostly unstable habitats in which development of climax woodland
vegetation is limited or prevented and they are often subject to erosion and
redistribution of water-borne material. The distribution of the different types of coastal
habitat is irregular and determined by a combination of geology and geomorpholo-
gical processes, but some, such as sand dune and salt marsh, are always limited in
extent, and machair is confined to the windy coasts of the western Highlands and
islands. With the exception of sea cliffs, much coastland is subject to considerable
human pressure, whether for recreation or agricultural, urban and industrial
development. If recent proposals for estuarine barrages and reservoirs come to
fruition, they will affect salt marshes and offshore sand and mud flats particularly.
Estuaries are especially under threat from urban-industrial development, e.g. deep-
water ports and installations, and industrial complexes such as those associated
with the exploitation of the North Sea oilfields. Coastal lowlands are also favoured
sites for nuclear power stations, aluminium smelters and steel mills.
Many of the habitats
and communities mentioned have been considerably modified
by human influence, and in this sense are no longer natural. Some, such as the
permanent grasslands of the lowlands, have been created by man from completely
different types, yet they are sufficiently similar to naturally occurring communities in
other places to be regarded as semi-natural. The Norfolk Broads were almost
completely artificial in origin, yet developed an almost completely natural character,
and have become one of the most important wetland complexes in the country. In
addition, the diversity of human activities has created numerous habitats and
communities which, though often populated by naturally occurring species, have
such artificial features that we cannot regard them as even semi-natural. This range
of artificial
ecosystems includes man-made habitats such as arable farmland,
roadside and railway verges, ponds, derelict land, hedges and walls. These are in the
aggregate of considerable importance to nature conservation, but are mostly too
highly fragmented and dispersed to be dealt with in terms of the key area concept.
The range of variation is nevertheless described, as an indication of the nature
conservation interest, but specific sites of importance are not mentioned, except
where they occur as a bonus interest in key sites chosen for their natural or semi-
natural ecosystems.
