San Francisco's Rare Endemic Manzanitas: Prospects for Recovery Through Restoration

Abstract

The Franciscan manzanita (Arctostaphylos franciscana) and Raven’s manzanita (A. montana subsp. ravenii) are rare shrubs endemic to San Francisco. Both taxa are federally listed as endangered species due to an extreme reduction in population and habitat area. This thesis reconstructs the environmental setting of historic locales to identify distribution patterns that may suggest essential suitability factors. Significant factors in the distribution of San Francisco’s endemic manzanitas were then analyzed across several manzanita taxa growing in maritime chaparral in the vicinity of San Francisco. Geologic substrate, slope position, overall slope curvature, and solar radiation emerged as important factors. These distribution parameters served as inputs to a heuristic model to select potentially suitable reintroduction sites. Finally, field surveys assessed current conditions at potential introduction sites to allow for comparison. Site comparisons revealed several potentially suitable reintroduction sites in San Francisco. Among potentially suitable sites, the Presidio of San Francisco contains the largest and most protected locations.