The Issue

The Presidio's historic forest is made up primarily of three species: blue gum eucalyptus from Australia and Monterey cypress and Monterey pine, both of which are native to California but not to the San Francisco area. These dominant species have cultural value for several reasons. A February 2002 draft "statement of significance" for the Presidio historic forest stated that it was significant for "its association with principles and practical applications of landscape design, including ideas related to aesthetics and parks; for its connection to forestry; for its association with San Francisco community development; and for its association with the Presidio's evolution as a military reservation on a uniquely sited landscape." The historic forest now also provides many natural values, including wildlife habitat, protection of water quality, and protection from strong ocean winds. Many of the trees, however, are nearing the end of their natural life span and will need to be replaced.

Resource managers are currently developing a vegetation management plan (VMP) to address tree replacement within the historic forest. A challenge arose in determining which species, native or nonnative, to plant as replacements, and the amount of diversity to create within replacement stands. Even the definition of natural or native vegetation is in question, because the vegetation at the time of European American settlement was limited to coastal scrub, willows, and oaks. Many natural resource professionals prefer to take a broader view and include trees native to the San Francisco area or to California generally as part of the native plant palette. Cultural resource specialists would like to determine the character-defining features of the historic forest—"the characteristics and features that define and illustrate the significance of the landscape"—and manage the site to maintain those features. These might include characteristics such as tree crown spread, canopy color, height, and individual species selection.

Proponents for creating a more "natural" forest maintain that species diversity would produce a healthier, more stable forest and protect against potential catastrophic loss due to disease. Vegetative diversity would also increase the overall biodiversity of the forest. Some members of the public have expressed the idea that the national park system is not the place for forest "plantations" or the planting of nonnative species.

Others would like to preserve the historic integrity of the forest by replacing mature trees with the same species to the greatest extent possible. One opinion expressed was that creating a diverse forest of native California trees would be creating a "cultural relic" of the year 2000 based on today's values, just as much as the existing historic forest is a "cultural relic" of the late nineteenth century.

A return to natural vegetation for the Presidio would be a return to coastal scrub, which would be viewed by neighboring property owners as reducing property values. It would also disregard the importance of the forest as a windbreak that forms a microclimate for park users, a valuable asset in an urban recreational park setting.

The scope of the VMP addresses all vegetation including native plant communities and the vegetation of the historic designed landscape as well as the historic forest. Other issues needing to be addressed in the VMP include the management of hazard trees, which result from the death of mature trees that become structurally unsound and create safety problems, and the maintenance of viewsheds. In the past, the Army has "topped" trees that blocked views at the request of neighboring property owners. This has resulted in deformed trees along the edge of the park. These neighboring property owners have a long association with the Presidio and are concerned about site management, so it has been important to include them in decision-making along with members of the larger San Francisco public.

Many of the buildings within the national historic landmark district are being rented as part of a for-profit leasing program administered by the Presidio Trust. In managing the vegetation in the historic designed landscape, resource managers must work with tenants to help them understand the significance of and reason for maintaining historic plantings and the potential threat posed by introduced species to native vegetation.