EFFECTS OF FOREST FRAGMENTATION ON THE SPATIAL GENETIC-STRUCTURE OF ACER-SACCHARUM MARSH (SUGAR MAPLE) POPULATIONS

To examine the effects of forest fragmentation on within-population genetic structure of Acer saccharum, the spatial distributions of allozyme variation in the first-year seedling cohorts of four forest patch populations (patches) were compared with those of four populations within continuous forest (controls). Forest patch populations exhibited less spatial mixing of genotypes than controls at the smallest scale examined (10-14.1 m), possibly as a result of reduced overlap of seed shadows in patches, which generally had lower densities of reproductive trees. Patch populations exhibited ter mixing of genotypes than controls at the largest scale examined (113.1-141.4 m), possibly as a result of the incorporation of immigrant pollen pools into mating events at forest patch edges. This may extend the spatial range of patch population breeding associations which might otherwise be truncated owing to limited forest patch area. Overall, results suggest that mating events are probably the primary determinant of spatial genetic structure within these cohorts in both forest patch and control populations of A. saccharum and that forest fragmentation has affected genetic structure by changing patterns of gene flow within, and possibly among, forest patch populations.