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 ge netic structure of Acer saccharum, the spatial distributions of allozy me variation in the first-year seedling cohorts of four forest patch p opulations (patches) were compared with those of four populations with in continuous forest (controls). Forest patch populations exhibited le ss spatial mixing of genotypes than controls at the smallest scale exa mined (10-14.1 m), possibly as a result of reduced overlap of seed sha dows in patches, which generally had lower densities of reproductive t rees. Patch populations exhibited ter mixing of genotypes than control s 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 f orest patch edges. This may extend the spatial range of patch populati on breeding associations which might otherwise be truncated owing to l imited forest patch area. Overall, results suggest that mating events are probably the primary determinant of spatial genetic structure with in these cohorts in both forest patch and control populations of A. sa ccharum and that forest fragmentation has affected genetic structure b y changing patterns of gene flow within, and possibly among, forest pa tch populations.