FINE-SCALE GENETIC STRUCTURE OF A TURKEY OAK FOREST

Theoretical models and computer simulations of the genetic structure of a continuous population predict the existence of patches of highly inbred individuals when gene flow within the population is limited. A map of the three genotypes of a two-allele locus is expected to exhibit patches of homozygotes embedded in a matrix of heterozygotes, when gene flow is limited. A search for such patch structure was made on a 160 × 160 m plot within a continuous 60+ ha old-growth stand of Quercus laevis (turkey oak). Approximately 3400 trees were genotyped for 9 polymorphic loci using starch-gel electrophoresis, and the genetic structure was analyzed with spatial autocorrelation (both nominal and interval), hierarchical F statistics, and number-of-alleles-in-common. Adults (diameter at breast height > 0) and juveniles were analyzed separately but showed similar structure. While no distinct patch structure was found, a greater degree of relatedness was observed on a scale of 5 m-10 m than at greater distances, probably because of the limited acorn dispersal from maternal trees and a small amount of cloning by root sprouts. A computer simulation of a 10,000 tree forest breeding for 10,000 yr indicates that the effective neighborhood sizes (of randomly drawn seed- and pollen-donors) are both in excess of 440 individuals. The model thus cannot distinguish the observed data from panmictic mating.