Edge effects from exotic tree plantations and environmental context drive dung beetle assemblages within Amazonian undisturbed forests

Abstract

Large-scale exotic tree planting programmes are widespread in the tropics and growing in the Brazilian Amazon – initially to meet global timber and cellulose demands and now as a nature-based solution to fight climate change and promote global ecosystem restoration. However, we still lack an understanding of how far might edge effects of exotic tree plantations spread into the interior of neighbouring tropical forests. Moreover, few studies have demonstrated how Amazonian forest insect populations may change in response to proximity to exotic tree plantations and along continuous (rather than categorical) gradients of environmental changes. We address these knowledge gaps by investigating how Eucalyptus plantation proximity, litter biomass, soil structure, and canopy openness influence distinct dung beetle responses surveyed within 34 plots of undisturbed primary forest in the Brazilian Amazon. Although the impacts of Eucalyptus plantation proximity were species-specific and varied across behavioural guilds and community metrics, we show that exotic tree plantation edge effects were the main driver of most dung beetle responses, penetrating up to 500–800 m into the forest interior. Dung beetle responses also varied along gradients of soil texture, canopy openness and leaf litter biomass, highlighting the importance of environmental context for dung beetle assemblages and populations. Overall, our findings for dung beetles show that the ongoing expansion of exotic tree plantations may affect our ability to maintain and conserve forest-specialist biodiversity due to edge effects in adjacent tropical forests.