Effects of dispersal, population delays, and forest fragmentation on tree migration rates

Examining the relation between the dispersal of seeds across landscapes and the migration of species can inform studies of processes such as invasions and response to climatic change. In this research a spatially explicit model is used to analyze the effects of dispersal probability, limits on establishment, generation time, seed crop probability, and varying proportions and patterns of landscape fragmentation on migration rate. Comparisons are made with rates inferred for migrations based on isopols of species range changes in the Holocene (20–200 km/century). The effects of the parameters on migration rate in the model are additive. Dispersal probability, related to diaspore type, is the most influential factor. Limits on establishment show effects only if severe. Lower seed crop probabilities can slow migration slightly. Generation times of 10 to 40 yr reduce migration rate moderately, while generations set long enough to reflect population doubling times would slow migration greatly. Extensive fine-scale fragmentation slows migration more than a single large barrier, but not greatly; multiple large barriers have greater effects. The factors have their greatest absolute and relative effects at higher dispersal probabilities; this result indicates that combinations of low dispersal probability and slow population development could increase the differences in migration rate among species while fragmentation could reduce these differences.