Conservation of endemic plants in serpentine landscapes Original Research Article

Serpentine outcrops in northern California occur in a variety of configurations, from scattered small patches to extensive landscapes covering hundreds of square kilometers. These areas support a distinctive flora with numerous uncommon or rare endemic species. I studied the reproductive ecology of two endemic plant species on large and small serpentine outcrops. The perennial herb, Calystegia collina, exhibited significantly lower reproductive success on small outcrops, partly because compatible pollen was not available from other, nearby populations. Local populations are more likely to produce seeds, and therefore potential colonists, when they occur in clusters of populations. Number of alleles and average heterozygosity were not significantly different between C. collina patches in small versus large outcrops. Vegetative reproduction enables small patches to persist for many years and apparently maintains genetic diversity despite low levels of seed production. Pollinators and insect herbivores of C. collina were not significantly less numerous on small outcrops than on large outcrops, suggesting that species interactions are not directly responsible for reproductive failure on small outcrops. The annual herb, Helianthus exilis, was entirely absent from small outcrops. This locally distributed serpentine endemic is restricted to moist seeps, a specialized microhabitat found only within large serpentine outcrops. Transplant experiments showed that H. exilis survives poorly or not at all outside these narrow conditions. Results from these investigations illustrate the need to protect serpentine landscapes that contain multiple local populations and the full range of microhabitats that are inhabited by serpentine endemic plants.