Community dynamics: What happens when we rerun the tape?

The role of historical events, such as disturbances, in producing alternative developmental outcomes in forest structure has long been debated. Diversity in the assemblages of coexisting species is one measure of alternative outcomes of succession. The intermediate disturbance hypothesis proposes that a moderate disturbance level produces the highest levels of species diversity. Here, we use an agent-based model of forest development under a gradient of lightning strike frequency to analyse long-term dynamics of species coexistence in a multispecies forest. The configurations of species that result from disturbance dynamics reflect the interactions between life-history characteristics of the species and disturbance characteristics. Model results suggest that low levels of disturbance lead to highly ordered landscapes which exclude fire and are captured by late successional species. High levels of disturbance lead to oscillation between domination by early successional species and large disturbances. At intermediate levels of disturbance, the forest displays the broadest array of developmental pathways, highest entropy as measured by Shannon's index of diversity, and critical slowing near steady states. Long transients at intermediate regimes may reflect the working out of closely balanced constraints of competition between species with varying strategic adaptations to disturbance. Intermediate disturbance levels also result in the greatest number of alternative diversity configurations as outcomes of succession, reflecting an unpredictable and nonequilibrium forest dynamic. (C) 2000 Academic Press.