The Peninsula Watershed, located in San Mateo County on the San Francisco Peninsula, is the site of three of the Bay Area’s largest reservoirs—San Andreas, Upper and Lower Crystal Springs, and Pilarcitos—which provide drinking water for residents throughout region. Encompassing the upper portions of San Mateo Creek and Pilarcitos Creek watersheds, the “Peninsula Watershed” also supports some of the largest intact remnants of contiguous habitat in the region, including extensive oak woodlands, old-growth Douglas Fir forests, serpentine grasslands, and chaparral. These habitats support the highest concentration of rare, threatened, and endangered species in the nine-county Bay Area, including San Mateo thornmint (Acanthamintha [obovata ssp.] duttonii), Fountain thistle [Cirsium fontinale], San Francisco garter snake (Thamnophis sirtalis tetrataenia), and Marbled murrelet (Brachyramphus marmoratus).
The 23,000 acres comprising the Peninsula watershed lands have been owned and maintained by the San Francisco Public Utilities Commission (SFPUC) since 1930, and prior to that by the Spring Valley Water Company. Despite early hydrologic modifications, the watershed has remained largely undeveloped and is managed to protect water quality, water supply, wildlife habitat, and a range of other natural and cultural resources. Over the past two centuries however, changes in disturbance regimes and other large-scale anthropogenic modifications, including fire suppression, grazing removal, introduction of pathogens (e.g., Phythophthora ramorum, which causes sudden oak death), spread of invasive species, and climate change, have altered vegetation dynamics and changed the distribution and structure of vegetation communities throughout the watershed.
This historical ecology study aims to advance understanding of the pre-modification conditions of the Peninsula Watershed, and to provide insights in to the nature and drivers of vegetation change since the first Spanish explorers set foot in the watershed nearly 250 years ago. Findings from the study will support the SFPUC and other land managers in the development of restoration targets, and provide context for envisioning future landscape potential.