Forest dynamics, differential mortality and variable recruitment probabilities

Abstract

Abstract. Both spatial and temporal variability in recruitment probabilities can lead to coexistence in gap‐phase regenerating forests which would otherwise tend to be dominated by fewer species. Using modified Markov models, the potential roles were examined of temporal variability and differential mortality rates among species in the dynamics of a forest for which spatial variability has been rejected as a strong factor leading to coexistence. Differential longevity modifies results obtained from a simple Markov model: it exerts a strong influence on the equilibrium species composition, on the rate of community change and on the time a community requires to reach equilibrium. Simulations with varying transition probabilities mimicked a changing climate, producing four main results: 1. Unless the duration of climate states is very long or very short, forest composition is in a continual state of disequilibrium. 2. Species vary in their response times to changing climate. 3. The mean abundance of each species under a varying climate scenario is different from that expected from the mean climate state. 4. The rare, long‐lived species was favored by climatic fluctuations at the expense of more common shorter lived species. Differential mortality rates provide an equilibrium‐based mechanism for coexistence, and temporally fluctuating recruitment probabilities a non‐equilibrium mechanism. Composition could be maintained by differential longevity among species and climatic fluctuations allowing periodic recruitment of the less common species.