Genetic subpopulation structuring and its implications in a mature eastern white pine stand

We examined patterns of genetic structuring within a mature eastern white pine (Pinus strobus L.) forest, using geographic information system (GIS)-based data and maps that combined genetic (isozyme analysis of 46 loci) and other tree-specific information (e.g., size, growth, age, and location) for 220 trees in Jericho, Vermont. Interconnections between genotypic information with other tree characteristics revealed several patterns of genetic structuring. Average observed heterozygosity generally increased with tree age-class, and trees with a high number of rare alleles were disproportionally represented in suppressed crown classes. Spatial structuring was also evident: trees within 5 m of one another were highly related, and levels of relatedness generally decreased with increasing distance between trees. In general, a 35-m-radius circle around any tree circumscribed its zone of genetic similarity. Hierarchical cluster analysis indicated the stand consisted of five family groups that exhibited greater genetic similarity within than among clusters. Temporal structuring (a generation gap) was also evident: trees of similar age showed significant positive relatedness, as did trees 30-40 years apart. Patterns of genetic structuring likely resulted from the combined influences of natural selection, isolation by distance, and functional generation times. Genetic structuring may also have biological and management implications. Computer-based simulated harvests suggested that the stand could experience genetic alteration when tree removal criteria disrupted existing structural patterns.