Landscape sensitivity: an ecological view

This paper briefly explores the concept of landscape sensitivity from an ec ological perspective by addressing the questions: what is landscape, what i s landscape sensitivity, what are the mechanisms of change. and what can la ndscape change mean for the species living there? Landscape to an ecologist is the vegetation and associated faunal populations draped over the geomor phology that give it most of its colour and texture. The concept of landsca pe sensitivity seems little used in ecology, and is taken here to mean inst ability versus stability. This is then explored, using examples mainly from the uplands of Scotland, but beginning with the fact that the vegetation c over over much of Scotland changed during the period 1946-1988, with for ex ample 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 depend ency of detected change, i.e. changes in particular attributes may go in op posite directions at contrasting spatial scales. Mechanisms of vegetation c hange, particularly the effects of grazing on vegetation, are discussed. Wi thin the physiognomic gradient from grassland to woodland in the Scottish u plands, there are two broad thresholds of grazing pressure. When these thre sholds are crossed, contingency effects can be particularly important in co ntrolling the ensuing successions. Also, when vegetation changes, labile so il properties such as pH can also change, with feedback effects on the spec ies composition of the vegetation. Finally, the implications of landscape c hange for species in upland Scotland are exemplified by changes in birds an d vascular plants. (C) 2001 Elsevier Science B.V. All rights reserved.