Heavy impact on seedlings by the impala suggests a central role in woodland dynamics

Research has increasingly established that mesoherbivores influence the regeneration of woody plants. However the relationship between mesoherbivore density and degree of impact, and the spatial component of this impact, has not been well established. Using a novel sampling design, we assessed in iMfolozi Park, South Africa, the impactofimpala(Aepycerosmelampus)acrossthefullcomplementofwoodyspecieswithinthehomerange,evaluating its spatial component and relationship to impala density. We used four GPS collars, in separate breeding herds, and a GIS to detect zones of different density of impala in the landscape, thus defining a fine-grain browsing gradient. We assessed impact on woody recruits (≤0.5 m height) across this gradient by means of 1600 random 1 ×1-m quadrats. Densitiesofwoodyseedlings,andmeanpercentageofremainingcanopy,weresignificantlylessinareasofhighimpala densityversuslow-densityareas.Therewasasignificantcorrelationbetweenincreasingimpaladensityanddecreasing density of favoured woody recruits. We propose a hypothesis of impala-induced patch dynamics. It seems likely that the ubiquitous impala may create and sustain a shifting mosaic of patches, and thus function as a key determinant of landscape heterogeneity.