Changes in vegetation diversity and composition following livestock removal along an upland elevational gradient

Abstract

European heathland habitats are cultural landscapes derived from previously-forested ecosystems. Heathlands are of significant conservation interest but have experienced prolonged degradation due to a range of factors including overgrazing by domestic livestock. There is growing recognition of the need to restore upland landscapes to produce a diverse mosaic of woodlands, heathlands and forest edge ecotones. In some studies stock removal has been sufficient to promote heathland recovery, but often more intensive interventions are required. Few studies have specifically examined how abiotic gradients associated with changing elevation might relate to restoration success. We examined differences in vegetation between grazed and restored areas over a 500 m elevational gradient split across two hillsides that were part of a landscape-scale restoration project in the Scottish Southern Uplands. Species alpha and gamma diversity showed non-linear responses to elevation but the effects of grazing differed between sites. Grazing increased diversity on the lower elevation site but reduced it at higher elevations. The differing effects of grazing with elevation can be interpreted in the context of levels of competition and likely impacts on rates of colonization and extinction. Differences in community composition were assessed using PERMANOVA, NMDS and Cluster Analysis and were primarily controlled by elevation with no significant effect of grazing. The keystone heathland species Calluna vulgaris was not recorded in any of our monitoring plots but some other dwarf shrubs were common. Changes in community structure following stock removal are slow on upland sites but initial impacts interact strongly with abiotic site conditions and pre-restoration vegetation composition. During large-scale restoration it is therefore vital to consider how widely-applied treatments might differ in their effects across landscapes. Changes in diversity may provide a useful early indicator of important ecological processes and likely directions of change.