Effects of introduction and exclusion of large herbivores on small rodent communities

Abstract

In this study we analysed the effects of large herbivores on smallrodent communities in different habitats using large herbivore exclosures. Westudied the effects of three year grazing introduction by red deer(Cervus elaphus L.) in previously ungrazed pine and oakwoodland and the exclusion of grazing by red deer, roe deer(Capreoluscapreolus L.) and mouflon (Ovis ammon musiminL.) in formerly, heavily grazed pine woodland and heathland. At eight exclosuresites within each habitat type, small rodents were captured with live trapsusing trapping grids. At each trapping grid, seed plots of beechnuts(Fagus sylvatica L.) and acorns (Quercusrobur L.) were placed to measure seed predation by rodents.Exclusion of grazing by large herbivores in formerly, heavily grazedhabitats had a significant effect on small rodent communities. Insideexclosureshigher densities of mainly wood mice (Apodemus sylvaticusL.) and field voles (Microtus agrestis L.) were captured.Introduction of grazing by red deer appeared to have no significant negativeeffects on small rodent communities. The seed predation intensity of beechnutsand acorns by small rodents was significantly higher in ungrazed situations,particularly in habitats that were excluded from grazing. The differencesbetween grazing introduction and exclusion effects on small rodent communitiescan be explained by differences in vegetation structure development. Therecovery of heavily browsed understory vegetation after large herbivore grazingexclusion proceeded faster than the understory degradation due to grazingintroduction. Small rodents depend on structural rich vegetations mainly forshelter. We conclude that large herbivores can have significant effects onvegetation dynamics not only via direct plant consumption but also throughindirect effects by reducing the habitat quality of small rodent habitats.