Ph.D. Dissertation Abstract by Regina Marie Rochefort (1995)

Phyllodoce empetriformis and P. glanduliflora are persistent and widespread species in mountainous areas of the Pacific Northwest. Although these species are quite common, little information is available on the population dynamics or reproductive biology of the species. In National Parks, increasing recreational demands escalates the potential for damage to these populations. This study describes genetic and morphologic diversity of heather populations in Mount Rainier National Park, assesses the potential influence of human use, and utilizes the information to propose strategies for long-term protection of heather populations.

Allozyme analysis was used to estimate genetic diversity of P. empetriformis and P. glanduliflora. Study sites were established at high and low elevation in three locations within Mount Rainier National Park. Analysis indicated high levels of genetic diversity within populations and significant differences in allele frequencies among populations and study areas. Heather populations are composed of multiple clones with high ratios of local to widespread genotypes.

Morphologic variation was surveyed through measurements of field and greenhouse populations. Significant differences existed among field populations for the four characters measured: annual stem extension, plant height, leaf width and leaf length. Greenhouse populations exhibited significant differences among populations for leaf width (P. empetriformis) and leaf length (P. glanduliflora).

The role of tree establishment in long-term heather survival was examined. Significantly more trees establish in heather populations than in plant communities dominated by other species. Survival of Abies lasiocarpa seedlings was significantly higher in heather populations than populations of other species. Low-elevation heather populations growing on topographic convexities often provide safe-sites for the establishment of tree seedlings.

A simple simulation model was developed to estimate the potential impact of human use on heather populations. Number of genotypes, allele frequencies, observed heterozygosity, number of live plants, and heather crown cover were calculated before and after simulated human use. No significant differences were found in allele frequencies or heterozygosity levels even after severe impacts were modeled. Genotypic diversity is not a sensitive indicator of human use. Numbers of genotypes only showed significant changes when impacts were very large or when restoration programs were initiated.