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THORNE
& HATFIELD MOORS CONSERVATION FORUM
What is peat?
All peatlands, including bogs, develop in waterlogged conditions
where dead plants decay slowly because of a lack of oxygen.
The result of this in-situ accumulation of organic matter is
peat. The rate of decay is so slow that the dead plant remains
can resemble the living material even after several thousand
years.
The term peatland refers to any wetland which contains peat,
whether or not the natural vegetation and hence the processes
of a peat-forming system still survive on the site. A mire is
a wetland which supports at least some vegetation that is normally
peat-forming. In some cases, the terms mire and peatland are
synonymous, but when all trace of peat-forming vegetation has
been lost, a peatland is no longer a mire. Equally, there are
some mires where, despite the presence of species which are
normally peat-forming, special circumstances have prevented
the accumulation of peat.
In their natural state, peatlands, or more accurately mires,
support distinctive assemblages of
plants and other wildlife, including many species which depend
on mire ecosystems for the
major part of their natural distribution. Much of the natural
heritage interest is derived from
systems which are capable of accumulating peat. Peat accumulates
largely because the decay of
plant material is inhibited by waterlogging. Conditions which
favour the development of a
vegetation which is normally peat-forming vary widely in Britain,
thereby giving rise to different
kinds of mire. Here, a distinction between fens and bogs is
important.
Fen systems are fed by direct precipitation and by water passing
through the underlying mineral
subsoil, sediments and rock, or by water which drains from the
surrounding catchment as surface
runoff or as lateral seepage. Thus, for example, fens may occur
at the margins of lakes, on river
flood plains and where there are springs or seepages. Fen systems
may vary from base-rich to
base-poor depending upon the soluble cations available from
the surrounding and underlying
geology, particularly calcium and magnesium. They may also vary
from nutrient-rich to
nutrient-poor depending on the levels of phosphorus and nitrogen
available in solution.
Not all fens are peat-forming, particularly where rates of water
flow and/or high solute concentrations result in rapid breakdown
of organic matter. Some fens may also be the ecological precursors
of bog systems. Under appropriate management, usually involving
intensive drainage, fen soils can support productive agricultural
systems. Extensive tracts of fenland in Britain, indeed throughout
Europe, have been drained for this purpose.
Bogs are found where there is no contact
with the groundwater and the only source of water is rainfall.
Only a few plants, such as the Sphagnum bog mosses, can cope
with the extreme sterile and highly acidic conditions.
Types of bog
Raised bogs form in the lowlands as single isolated domes of
peat in an otherwise non- peat landscape. As peat accumulates,
the bog rises from the surrounding land. The range of species
found in bogs throughout the UK and Europe differ. The easy
access to these bogs and their highly prized, deep moss peat
make them prime targets for commercial exploitation for horticulture.
Bog systems are peat-forming mires which are fed by atmospheric
precipitation - rainfall, snow,
mist and dust alone. During otherwise dry periods (i.e. no rainfall),
occult precipitation from
mist, cloud or low-lying fog may influence the surface water-balance
or, alternatively, prevent
drought-stress in the main peat-forming species. Analyses of
bog-pool waters show solute
concentrations reflecting closely the inputs derived from rainfall.
Bogs are, by definition,
nutrient-poor and acidic, but are differentiated from fens with
similar ion balances on the basis of
their solute and water sources.
Two main types of bog have been described
in Britain - blanket bog and raised bog. Their
geographical distribution reflects regional differences in climate.
Lindsay (1995) provided a
summary of these two types, and two more restricted forms, together
with a synthesis of their
ecological characteristics.
In Britain, lowland raised bogs typically occur as isolated
and slightly elevated features in the
landscape, sometimes forming complexes of several "raised"
domes of peat, which are
hydrologically distinct. They are typically surrounded by highly
managed farmed or forested areas.
The importance
of raised bogs
Scientists from many disciplines recognise the importance of
raised bogs. Climatologists, archaeologists and biologists value
the peat archives in the living bogs as essential to research;
and naturalists cherish the living carpet that covers the peat.
Raised bogs help to maintain reliable supplies of clean water
to rivers. They also have a cultural importance as some of the
last true wilderness areas in the lowlands, and are enjoyed
by thousands of people. We are only just beginning to understand
the ecology of peat bogs and their importance to the global
environment. We must safeguard this natural treasure for future
generations and not destroy it for short-term gain.
A living archive
Peat bogs contain an unparalleled record of our past. A rich
archive of information lies preserved in bogs. Much of this
is organic, and has a capacity to expand our understanding of
people, culture, economy and climate far back into prehistory.
Pollen, plants, evidence for the use of wood and woodland management,
boats, weapons, lines of communication and indications of human
impact on surrounding landscape and ecology all contribute to
modern knowledge in ways which are seldom approached on dry
land. Peat bogs have produced some of the most spectacular finds
of British archaeology, including remarkably well-preserved
bodies of some of our ancestors. Peat extraction on an industrial
scale -as opposed to more modest, non-mechanical methods ot
former times -is a crude and destructive method of discovering
theses treasures. The archaeological evidence does not regenerate.
Carbon store
Peat is rich in fossil carbon, removed from the atmosphere by
plants and accumulated over thousands of years. Drainage and
destruction of raised bogs results in the rapid loss of the
stored carbon in the form of greenhouse gases, as the peat decomposes.
The wildlife importance of many raised bogs is recognised in
their notification as Sites of Special Scientific Interest (SSSIs)
under the Wildlife and Countryside Act 1981 (as amended) or
as Areas of Special Scientific Interest (ASSIs) in Northern
Ireland under the Nature Conservation and Amenity Lands (NI)
Order 1985. More recently EC Council Directive on the Conservation
of Wild Birds (79/409/EEC) allows important sites fulfilling
specific criteria to be designated as Special Protection Areas
(SPA), the EC Directive on the Conservation of Natural Habitats
and of Wild Fauna and Flora (92/43/EEC) frequently referred
to as the Habitat Regulations similarly allows designations
as Speacial Areas of Conservation (SAC).
The thin living layer that carpets the bog consists largely
of Sphagnum mosses, ranging from brilliant green to ochre red.
Unusual plants, such as the sundews, butterworts and bladderworts,
supplement their diet in their nutrient-poor environment by
catching and digesting insects. This very sterility prevents
other, less specialised species from colonising peat bogs, but
it is also one of the reasons why bog peat is valued so highly
by horticulturists as a growing medium.
Raised bogs are important for the conservation of several rare
plants and animals. Some of our rarest insects, including the
large heath butterfly, mire pill beetle and several species
of dragonflies, thrive in the wet conditions. Plants such as
bog rosemary are found nowhere else in the UK. The mossy hummocks
and pools provide vital nesting and feeding grounds for wading
birds. These birds depend on Europe's disappearing wetlands.
The overall mixture of plants and animals make raised bogs
unique and valuable places. They become islands of typically
upland species in lowland areas. Breeding birds such as the
teal, golden plover and dunlin are usually found only in the
far north, but on some raised bogs they can be found alongside
more southerly species such as the nightjar.
As with much legislation chronology plays an important role,
and in the case of the extant mineral extraction planning consents
granted in the 1950’s on Thorne and Hatfield Moors they pre-date
wildlife legislation and for local authorities or government
to intervene and revoke consents incurs considerable cost in
terms of compensation payments.
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