ASSOCIATIONS BETWEEN ENVIRONMENTAL HETEROGENEITY, HETEROZYGOSITY, ANDGROWTH-RATES OF POPULUS-TREMULOIDES IN A CORDILLERAN LANDSCAPE

The relationship between mean annual incremental growth, habitat heter ogeneity and heterozygosity at 14 polymorphic loci was studied in a na tural population of trembling aspen (Populus tremuloides) in the premo ntane-montane region of Waterton Lakes National Park, Alberta, Canada. Multiple correlation of mean annual incremental growth in relation to elevation, aspect, exposure, slope, slope position, and age of the ol dest standing ramet explained 56% of the variability in growth. A posi tive correlation was found between an individual tree's growth rate an d its degree of heterozygosity after controlling for environmental inf luence. There was also a positive correlation between growth and the d egree of heterozygosity when clones were grouped into heterozygosity c lasses. Mean annual incremental growth was most strongly associated wi th heterozygosity at the G6PD, ADH, ALD, and G2DH loci; growth rates w ere higher in heterozygotes than homozygotes. The differences in heter ozygosity might be attributed to the enzyme loci involved in regulator y functions. The implications of these results for forest structure an d succession are discussed.