Population Genetics and Spatial Autocorrelation in an Unmanaged Stand of Quercus petraea in Denmark

An unmanaged stand of Quercus petraea (Matt.) Liebl. in Denmark was studied for morphological and microsatellite variation. The sample of 339 trees, which is part of a European network of similar oak stands, revealed a unimodal (single) distribution of Q. petraea but found evidence for extreme morphological variation expressed by a number of trees. While hybridization with Quercus robur may be one reason for such a pattern of variation, other possibilities exist. Variation at six microsatellite loci indicated no correlation with any of the nine morphological traits investigated, and showed only small deviations from Hardy-Weinberg proportions. The levels of observed heterozygosity and allelic diversity were similar to those found within other stands of Q. petraea in central Europe, and no reduction in diversity was evident for the Danish stand despite its being situated at the margin of the distribution of the species. Weak, but significant, spatial genetic structure was identified using Moran's index, but the level of spatial autocorrelation was found to be dependent on locus, allele frequency and sample size, which should be greater than 100 trees to identify spatial patterns. Spatial genetic structure was found to be higher for trees with a diameter at breast height (dbh) of <40 cm than for larger trees (>40 cm dbh) and this is thought to reflect a balance between the influence of limited seed dispersal, which will act to establish genetic structure in younger generations, and selection, which will disrupt genetic structure in older generations. The life history of the stand is discussed in relation to the observed genetic parameters.