The sensitivity of peat-covered upland landscapes
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Ombrogenous mires, or bogs, are remarkable in that they are organic landforms built from living plants and their partially decayed remains (peat), together with large quantities of water derived directly from precipitation. In the uplands and northwest of the British Isles, they tend to dominate landscapes wherever the slope allows. The components of ombrogenous mires are highly sensitive to change, especially in hydrology. Their vegetation may alter in response to very small changes in water level and/or water chemistry, whereas the underlying peat may undergo total degradation on dewatering. The function of intact mire ecosystems incorporates mechanisms which tend to maintain stability when environmental conditions change; observation indicates, however, that the stability threshold may be crossed under some natural as well as some man-induced circumstances. Sensitivity is demonstrated by evidence from the plant remains preserved in the peat; from manipulation of management practices (particularly grazing and burning); from long-term (28–68 years) mapping of vegetation change; and from experimentation on the sensitivity of bog plants to components of air pollution. The ultimate manifestation of sensitivity is peat erosion, which is widespread in the uplands and may, in places, have been ongoing for several hundred years. It is concluded that we may anticipate heightened sensitivity to cultural perturbation of mire ecosystems during times of climate change, and thus that particular care in our approach to management of blanket peat landscapes is indicated at the present time.