Aims: Habitat loss and fragmentation are the leading causes of global biodiversity decline. How fragmentation (leading to edge effects, increased isolation and declining habitat size) interacts with topdown processes like vertebrate herbivory, an important driver of vegetation structure and composition in many ecosystems, is poorly quantified. Interactions between fragmentation and changes in herbivory may exacerbate their individual influences on plant growth, with implications for management of native plant communities within fragmented landscapes. We examined the effects of habitat fragmentation on herbivore activity, and also how both fragmentation and mammalian herbivory influence growth of understorey plant species.
Methods: This study was conducted at the Wog Wog habitat fragmentation experiment, located in south-eastern New South Wales, Australia. We use herbivore exclusion plots across an experimentally fragmented landscape to assess the interactive effects of fragmentation and herbivory on the growth of four plant species that vary in growth form and rarity in the landscape.
Important Findings: We observed species-specific responses to both herbivory and fragmentation, but no additive or interactive effects between these drivers. We show that a reduction in herbivore activity within fragments does not correspond with an increase in plant growth, even for the most palatable species. Rather, top-down processes continue to operate across the fragmented landscape. Although changes in habitat conditions within fragments appear to negatively influence both plant growth and mammalian herbivore activity, it is likely that alterations to bottom-up effects (i.e. fragmentation) may be more important than top-down effects (i.e. herbivores) for the species under investigation. The species-specific response of plants to herbivory or fragmentation may have implications for temporal and spatial population persistence in fragmented landscapes and ultimately fragment vegetation structure.