Effects of the type of montane forest edge on oak seedling establishment along forest–edge–exterior gradients

Recent studies have highlighted the importance of different edge types in the modulation of edge-related responses associated with habitat fragmentation. Hard (high contrast with pastures) and soft (low contrast with old-fields) forest edges created by slash-and-burn agriculture have become common landscape features in regions dominated by Neotropical montane forest. The growth and survival of seedlings of five oak species (Quercus candicans, Quercus crassifolia, Quercus laurina, Quercus rugosa and Quercus segoviensis) was monitored experimentally by introducing seedlings across replicates of the forest–edge–exterior gradients (24, 12, 0, −12 and −24 m) typical for these two edge types (hard and soft) in the Chiapas Highlands, Mexico. Seedling survival and growth (measured in terms of basal area, new stem and leaf production, and defoliation) was generally greater in adjacent open habitats than in the forested portion of the gradient. However, seedling performance was optimal 12 m from the soft edges in the open habitat. Overall, Q. crassifolia had the lowest seedling survival, especially in the forested portion of hard forest edges, whereas Q. rugosa showed the highest growth rates and survival. This study shows that the edge effects detected along a forest–edge–exterior habitat gradient may depend in large part on the type of edge being studied. The implications of these results are discussed with respect to the influence of edge characteristics on forest patch dynamics in fragmented tropical montane landscapes.