sfenvironment.org

History of San Francisco's Urban Forest

In 1769, when the first Spanish soldiers and missionaries set foot on the peninsula that later became San Francisco, the native vegetation consisted primarily of low-growing shrubs, grasses, and ground covers that were perfectly adapted to the area's predominantly sandy soils, maritime climate, and strong coastal winds. Oaks and willows were among the native tree species, but the few native stands of coast live oak and California buckeye were cut down for firewood and nearly wiped out when the population exploded after the Gold Rush years.

In the 1870s, the San Francisco Board of Supervisors established the city's first municipal tree-planting program, creating significant forested areas like Mount Sutro Open Space Reserve, the Presidio, and Golden Gate Park. Famous landscape architect Fredrick Law Olmsted, who'd designed New York's Central Park, was hired to select a site for the latter. The esteemed Olmsted selected a site along modern-day Polk Street, but the city fathers thought better of it and instead chose to build Golden Gate Park on its present site. This meant that the western two-thirds of the park—mostly sand dunes—first had to be stabilized with plantings of barley and lupine, then transformed into the tree-filled pastoral landscape you see today.

Civil engineer William Hammond Hall designed the park and oversaw the planting of three species of trees, chosen for their tolerance of salt winds, poor soil, and summer drought: Monterey cypress, Monterey pine, and blue gum. By 1875, 60,000 trees had been planted; by 1879, 155,000. These species, and some of their relatives, are the backbone of San Francisco's urban forest in the city's most notable open spaces, creating windbreaks for a wide variety of more sensitive trees and shrubs. Some non-natives—like the eucalyptus and the blue gum—have come to dominate areas since they grow fast and have no competition from other trees.

Today, more than 100 native and nonnative tree species make up the city's diverse urban forest. And that variety is crucial: A diverse urban forest can withstand physical challenges like pests, disease, or climate change. If a pest or disease wipes out one tree species, the others will remain.

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