Landscape sensitivity: an ecological view

This paper briefly explores the concept of landscape sensitivity from an ecological perspective by addressing the questions: what is landscape, what is landscape sensitivity, what are the mechanisms of change. and what can landscape change mean for the species living there? Landscape to an ecologist is the vegetation and associated faunal populations draped over the geomorphology that give it most of its colour and texture. The concept of landscape sensitivity seems little used in ecology, and is taken here to mean instability versus stability. This is then explored, using examples mainly from the uplands of Scotland, but beginning with the fact that the vegetation cover over much of Scotland changed during the period 1946-1988, with for example ca. 50% or more change in vegetation types in about half of Scotland. The commonness and speed of change are stressed, and also the scale dependency of detected change, i.e. changes in particular attributes may go in opposite directions at contrasting spatial scales. Mechanisms of vegetation change, particularly the effects of grazing on vegetation, are discussed. Within the physiognomic gradient from grassland to woodland in the Scottish uplands, there are two broad thresholds of grazing pressure. When these thresholds are crossed, contingency effects can be particularly important in controlling the ensuing successions. Also, when vegetation changes, labile soil properties such as pH can also change, with feedback effects on the species composition of the vegetation. Finally, the implications of landscape change for species in upland Scotland are exemplified by changes in birds and vascular plants. (C) 2001 Elsevier Science B.V. All rights reserved.