Dispersal probability and forest diversity in a fragmented landscape

The diversity of forest stands may be affected by landscape fragmentation during periods of climatic change. A modified version of the JABOWA-FORET model of the dynamic processes of establishment, growth, and death of forest trees is used in a spatially explicit framework to elucidate differences in the effects of both spatial structure and spatial processes. In cases with and without climatic change, the effects of including random or structured fragmentation and successively lower dispersal probabilities (increased chance of long-distance dispersal) are examined in simulation experiments. The exclusion of very low dispersal probability (p < 0.001) has an important effect on species richness. Barriers and random fragmentation also lower diversity. Climatic change has little effect on diversity alone or in addition to fragmentation; changes in composition result. These results indicate that rare events, especially of the type seldom recorded in observations of seed dispersal, are extremely important. The results of our simulation experiments indicate that model scale must be addressed in more detail.