Landscape openness has different effects on the structure, diversity and functional composition of Brazilian rainforests

Abstract

Landscape openness leads to harsher environmental conditions and reduced propagule dispersal, but how it affects different forest attributes and over what spatial scale remains unclear. We evaluate the effects of landscape openness (i.e., increased forest loss and fragmentation) on nine forest attributes related to structure, diversity, and composition for four different spatial scales, and three regions in Brazilian Atlantic forest. For 35 0.1 ha forest plots we calculated nine forest attributes related to structure (basal area, maximum height, structural heterogeneity), tree biodiversity (species richness, Simpson diversity, functional richness) and functional composition (proportion of animal-dispersed and shade-tolerant species, seed size). To assess at what spatial scales landscape characteristics play a role, we calculated for each plot local matrix openness and forest patch density using four concentric circles of 400 to 3200 m radius. Landscape openness negatively affected most forest attributes, but the magnitude of effect varied with 1) landscape attribute, 2) forest attribute, and 3) region. First, matrix openness had a negative stronger effect than patch density, indicating that landscape forest loss is more detrimental than forest fragmentation. Second, landscape openness reduced most strongly forest structure and animal-dispersed species, probably because open landscapes increase edge effects which especially affect large-sized trees, and reduce the abundance and activity of zoochorous seed dispersers, while landscape openness had opposite effects on diversity in different regions. Third, landscape openness had different effects in different regions, probably because of regional differences in tree species composition, landscape configuration and composition. Finally, landscape openness affected forest structural attributes at all spatial scales, animal-dispersed species at larger spatial scales (>1600 m), and seed size at small spatial scales (<400 m). In sum, landscape openness reduced most forest attributes, although the strength varied with the landscape attribute, forest attribute, and landscape context. Conservation and restoration projects should therefore restore landscape forest cover to improve forest structure, diversity and composition, and take into account the landscape context.