Moorland development on Exmoor
Moors and heaths are common in Britain, but internationally they are very unusual. They are mostly found in the mild wet climates along the coasts of western Europe, Canada, Siberia and the southern tips of South America and New Zealand. Britain has 10-15% of the world's moorland. In Europe heathland can be found along the Atlantic seaboard from southern Norway to northern Portugal, but Britain has most as it provides ideal growing conditions for heather, the commonest heathland plant. There is more to moorland than just heather and the variety of habitats on Exmoor is impressive, 23 different communities of moor and heath as recorded in the National Vegetation Classification of Britain have been identified on Exmoor some of which are internationally rare.
Moorland appears natural and undisturbed but it was largely created by humans who utilised the prehistoric woodlands which covered the hills for fuel and fodder. People began to settle upland Exmoor in the Bronze Age, from about 1500BC. Following their clearance of the woodlands repeated burning and the grazing of domestic animals has kept the moorlands as open communities dominated by dwarf Shrubs, grasses and sedges. This is known from the analysis of Palaeo-ecological records such as pollen and macrofossils preserved in peat horizons on the moorland. It is also known that the climate became cooler and wetter at the end of the bronze age/beginning of the Iron Age (about 3,000 years ago). This combined with the loss of trees to erode and wash nutrients from better drained soils, increasing their acidity. This led to the development of an Iron pan and the eventual onset of blanket peat accumulation.
Peat accumulates in cool wet acid climates where the build up or dead material from vegetation exceeds the rate of decomposition. The bacteria and other animals which normally cause decay cannot survive in the acid, wet conditions where oxygen is rapidly used up. Dead plants just remain and are eventually compressed to form peat. Peat communities are charcterised by the Sphagnum Mosses which modify the soil conditions towards further acidity and wetness (due to their sponge like nature) and increased peat growth.
Today blanket peat deposits extend across much of the central upland areas, covering the evidence for past cultivation and habitation in a blanket of peat which reaches a depth of several meters in places. On the flatter plateaus, in hollows and in other spring fed or topographically wet areas the peat can be particularly deep and these areas are the most valuable in terms of the diverse Sphagnum and Cotton grass mire habitats and the extent of the Palaeo-ecological information locked away in their stratigraphic layers.
Peat is a valuable environmental resource as it locks up huge quantities of carbon dioxide, the main 'greenhouse' gas. It also acts like a sponge, soaking up rainwater and preventing floods, yet slowly releasing the water for when we most need it. To find out moor about PEAT and what the ENPA and its Partners are doing to protect it …go to the MIRE PROJECT PAGES
Across much of the Exmoor Forest moorland agricultural activity such as reclamation, liming, drainage, intensive grazing and burning has resulted in a modified peat deposit and blanket bog vegetation. The dwarf shrub/heather, Cotton Grass and Sphagnum Moss components has been largely lost and replaced by a purple moor grass dominated sward.
- In contrast the Commons around the edge of the Exmoor forest and the coastal areas have a heathland vegetation. The well drained hill slopes and sandy soils of these sandstone areas encourage the growth of ling and bell heather along with gorse, whortleberry and bracken. The grasses bristle-leaved bent and wavy hair grass are also important heathland plants. In order to keep the heathlands and heather dominated moorlands clear of trees and bushes regular burning or swaling is required in combination with controlled grazing.