Scaling-up ecological patterns and processes is essential for systematic conservation planning for the long-term. In a fragmented forest landscape, forest configuration affects the distribution and densities of potential animal seed dispersers, disrupting key biological processes such as seed dispersal, plant species recruitment and extirpation-colonization dynamics. In this study, we tested the influence of forest configuration and dispersal traits on the realized dispersal of tree species and their occurrence in a tropical humid forest of Madagascar.
First, remote sensing was used to make maps of forest and non-forest cover for the area of interest. Multi-temporal Landsat images were used. Images from 1990, 2000 and 2010 were collected to make the maps and landscape configuration metrics such as patch size, distance to neighbouring patch, distance to the edge and perimeter-area ratio. Second, 125 forest plots of 20m x 20m were established across the Ankeniheny-Zahamena forest, stratified with respect to forest configuration. Trees were identified to species and placed into approximate age classes. Dispersal traits (dispersion mode, fruit type, seed size, seed longevity,) were collected from the field and from the herbarium specimens. Third, I analyzed plot data and modelled prevalence of size classes of each species in relation to forest configuration properties of the plots when the individuals established and the dispersal traits of the species.
Vegetation configuration influenced the realized dispersal of tree species. For many species, individuals in the oldest age class occur more frequently inside forest interior and in larger patches whereas individuals in the youngest age class occur more frequently in smaller patches. Species showing lower adaptation to fragmentation are mainly passively dispersed, with fleshy fruits and medium seed longevity. These results suggest that correlative approaches for tree species distribution modelling could be improved by incorporating processes such as dispersal traits in order to permit better systematic conservation planning of tree species.