Disturbance and population structure on the shifting mosaic landscape

A stochastic model of plant population dynamics is developed and analyzed to determine how density and age structure depend on thinning rates and disturbance regimes. Probability distributions of age and density are derived from the distribution of regeneration niches on a landscape and the thinning rates of cohorts on patches created by adult mortality or larger disturbances. The theory is extended to different types of disturbances that operate at different scales and are interdependent, eg treefalls that only become important as the early-successional trees that initially colonize an area affected by a larger scale disturbance become mature. In general, landscapes that provide frequent regeneration niches support high-density young stands. Density distributions are negatively skewed. Decreasing frequency of regeneration niches results in lower mean density, higher variance, and increased (less negative) skewness. When regeneration niches are rare, density is low, variance is low, skewness is positive, and the age classes are highly variable. In more complex cases, regeneration niches may depend on the time since the last large disturbance; eg canopy gaps can become more frequent as postfire cohorts become senescent. The "intermediate' disturbance frequency that maximizes the probability of being reproductively mature at the time of the next disturbance event (see 91L/13196) is also that which maximizes the density of reproductive individuals on this shifting mosaic landscape. -from Authors

Duke Scholars

Author James S. Clark Environmental Sciences and Policy