Effect of distance to edge and edge interaction on seedling regeneration and biotic damage in tropical rainforest fragments: A long-term experiment

Abstract

In forest fragments, edge effects can influence forest regeneration, but little is known about how edge effects influence seedling performance and the interaction between seedlings and their natural enemies over time. In central Amazonia, we recorded survival and growth (in height and leaf number) and damage by insect herbivores and leaf-fungal pathogens of Chrysophyllum pomiferum (Sapotaceae) seedlings that were exposed to different numbers of edges and to different distances from the forest edge. Grown seedlings were transplanted into one-square-metre plots within 1-ha blocks located in the centre (no edge), the edge (one edge), and the corner (two edges), and at different distances from the edge towards the interior (i.e., 20, 40, 60, 80, and 100 m) of two rectangular fragments (10- and 100-ha in size). Plots were visited once every 2 months for 1 year (1992–1993) and thereafter every 2 years for almost 8 years (1993–2001). Overall, results showed that seedling survival, height, leaf number, and biotic damage varied over time with the presence of nearby edges and with the distance from the edge. Survival was lower in fragment edges and corners than in centres. Increase in height was similar for all positions within the 100-ha fragment, whereas in the 10-ha fragment seedling height had a greater increase at the edge and corner than in the centre. Furthermore, survival increased with distance from the edge as did leaf number, whereas height showed a lower increase closer to the edge than farther away. Regarding biotic damage, for both fragments herbivory was greater at the centres and decreased with edge proximity over time, whereas leaf-fungal damage was greater at the corners than in the edges and increased significantly over time. Biotic damage was correlated with seedling size. Small seedlings were more susceptible to fungal attack, whereas larger seedlings were so to herbivores. Synthesis. This study demonstrated that despite stochastic environmental factors seedling survival, growth, and biotic damage by herbivores and fungal pathogens varied with the level of edge exposure and proximity, which may threaten forest regeneration in the long term. © 2018 The Authors. Journal of Ecology © 2018 British Ecological Society