DISPERSAL PROBABILITY AND FOREST DIVERSITY IN A FRAGMENTED LANDSCAPE

The diversity of forest stands may be affected by landscape fragmentat ion during periods of climatic change. A modified version of the JABOW A-FORET model of the dynamic processes of establishment, growth, and d eath of forest trees is used in a spatially explicit framework to eluc idate 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 di spersal probabilities (increased chance of long-distance dispersal) ar e examined in simulation experiments. The exclusion of very low disper sal probability (p < 0.001) has an important effect on species richnes s. Barriers and random fragmentation also lower diversity. Climatic ch ange has little effect on diversity alone or in addition to fragmentat ion; changes in composition result. These results indicate that rare e vents, especially of the type seldom recorded in observations of seed dispersal, are extremely important. The results of our simulation expe riments indicate that model scale must be addressed in more detail.