Fine-scale genetic structure in Pinus clausa (Pinaceae) populations: effects of disturbance history

Spatial autocorrelation analyses of 12 allozyme loci were used to compare g enetic structure within populations of two varieties of Pinus clausa. P. cl ausa var. immuginata populations tend to be uneven-aged, with continuous re cruitment in small gaps created by wind damage, whereas P. clausa var. clau sa populations are more even-aged, with recruitment postdating periodic can opy fires. Three var. immuginata populations and three matched pairs of var . clausa populations, including both a mature and a nearby recently burned population, were examined. Aggregation of multilocus genotypes at small dis tances was evident in all young var. clausa populations. Little inbreeding was apparent among juveniles or adults in these populations; their genetic structure is likely to have resulted from limited seed dispersal. Genotypes were not significantly spatially structured in nearby matched mature popul ations. Genetic structure was less evident in var. immuginata populations. Aggregated genotypes were only apparent in the population where patches inc luded juveniles of similar ages; dense juvenile clumps in the other two var . immuginata populations comprised a variety of ages. Interannual variabili ty in allele frequencies of surviving seedlings may account for the absence of genetic structure in these populations.