Pinus ponderosa seeds from 50 trees in each of six small isolated stands located within a nine kilometer radius of Colstrip, Montana, were examined at 23 isozyme loci. Megagametophyte and embryo tissue from each seed were screened separately. Measures of genetic diversity showed no significant differences between male and female components within or between stands. The average proportion of heterozygous loci per embryo (He) was not significantly different between stands. For all stands combined, He was 0.012. Genotype proportions did not deviate from expected Hardy-Weinberg proportions.
Nearly 99 % of the genetic diversity resided within individual stands, with a significant 1.5 % due to differences between stands. Genetic distance between stands is not correlated with geographic distance. Considering the natural fire history of the stands, it is suggested that there is a great deal of gene flow into a stand during its early stage of development.