The ponderosa pine is one of the most ubiquitous forest trees of western North America, spanning both large altitudinal and latitudinal gradients. It is extensively harvested for timber. This species is very tolerant of drought and abnormal soils, is fire resistant, and it regenerates prolifically across a wide range of environments. Several varieties exist, and morphological, biochemical, and growth trials indicate that these varieties can be further differentiated into geographic races. Several questions remain to be addressed in light of the overall genetic diversity of the species, its ecological history as a recent invader of the forests of the western United States, and its susceptibility to range extensions and contractions linked to future climatic change. This research project will focus on marginal, disjunct populations of ponderosa pine in eastern California to determine levels of genetic diversity, to isolate the abiotic factors that control their distribution, and to document the life histories and demographies of these populations. Ecological sampling will be used to assess population variation and demography, and isozyme analyses of intra- and inter-population variation will measure genetic variation within and among populations. The approach integrates two levels of ecological analysis to examine biogeographic implications of climate change and geographical isolation for populations of this long-lived, widespread species. The distribution of genetic diversity in forest tree populations represents the potential of that species to adapt to and survive environmental change. Genetic diversity also reflects the evolutionary history of a species. This project will advance our current understanding of how genetic diversity is distributed among marginal and disjunct populations of a genetically wide-spread species. This information is crucial to breeding programs and efforts aimed at conservation of genetic diversity.
