The Presidio of San Francisco is a former U.S. Army base that was repurposed as an urban national park in the mid-1990s. The park exemplifies the idea of a socio-natural site: “a site of historical society-nature interactions” that have resulted in reciprocal natural and cultural adaptations of appearance and use.
The Presidio’s historic forest is a prime example of such adaptive interactions. The planting of the forest was proposed by a U.S. Army officer in 1883 and implemented between 1886 and 1910 for aesthetic, tactical, and strategic reasons. Today the forest may appear “natural” but is very much the product of “society-nature interactions” – intense human intervention and management in tandem with dynamic climatic and ecological conditions.
Anthropogenic changes bring unintended ecological consequences. One of the three introduced tree species, blue gum eucalyptus, is invasive and a fire hazard. On the other hand, the trees have served as crucial habitat for birds, with a resulting increase in local bird biodiversity. Most significantly, because the tree-planting period spanned less than three decades, the trees are reaching the end of their natural lifespan at approximately the same time.
In 1962, the forest became a protected landmark because of its historical importance to the development of the Presidio as a military base. Thus, even as the trees are dying, the agency that manages the park is charged with preserving the forest as is. To complicate matters further, the agency is required to replace the original non-native trees with the same non-native species – even as it expends considerable effort to restore native flora in other areas of the park. In being designated a historic forest, these trees reside in an enforced stasis that seems highly unnatural. This problematic situation arises in any site we humans decide should be “protected.” What is it protected from – the depredation of humans, or of nature?
Halloran, Pete, “Seeing the Trees Through the Forest: Oaks and History in the Presidio,” in Reclaiming San Francisco,San Francisco: City Lights Books, 1998.
“Restoring the Presidio Forest,” Presidio Trust website, http://www.presidio.gov/about/Pages/restoring-the-presidio-forest.aspx (21 March 2015).
Winiwarter, et al., “Looking at half a millennium of co-existence,” Water History, Vol. 5, No. 2 (2013), pp. 101–119.
Image: “A view the Main Post surrounded by the rolling hills of the Presidio empty of any structures or trees except for a few newly planted trees in the foreground.” Undated photograph, probably circa 1890. Courtesy Presidio Trust.