ABSTRACT

Human disturbance is widespread within tropical forests, with large tracts of once-continuous forest reduced in many cases to highly fragmented stands of trees. Formulation of management strategies for the conservation of tree species within such landscapes requires an understanding of the consequences of fragmentation for the levels and spatial distribution of genetic diversity and the extent of genetic connectivity between stands. The study investigated the genetic impacts of fragmentation in a population of the neotropical tree Swietenia humilis in a seasonally dry forest in Honduras. Microsatellite markers showed high levels of genetic variation over 10 loci, with little genetic differentiation across the sampled range. Comparisons of pollen flow within continuous forest to that within and between the fragments showed that although near-neighbour interactions predominate throughout, the proportion of long-distance pollen flow increased with a decrease in the population size of the fragments. At the extreme of isolation, a remnant tree in pasture, pollen flow up to 4.5 km was detected, with the proportion of pollen flow governed by the size of the pollen source rather than distance. Pollen donors were highly variable between trees, and influenced by both the frequency and the flowering phenology of surrounding trees, while seed production increased with an increased degree of disturbance. Fragmentation did not result in the reproductive isolation of the stands, but rather resulted in increased levels of long-distance pollen flow, possibly leading to restoration of rare alleles lost in the original fragmentation.