I love redwood trees. I doubt there is anyone who doesn’t. So, you might wonder why I am going to tell you why planting more of them in our public parks in the San Francisco Bay Area isn’t a good idea. Read on…
History of redwoods in California
The native range of redwoods is very small. According to the US Forest Service, “The redwoods occupy a narrow strip of land approximately 450 miles in length and 5 to 35 miles in width. The northern boundary of its range is…in the Siskiyou Mountains within 15 miles of the California-Oregon border. The southern boundary of redwood’s range is…in the Santa Lucia Mountains of southern Monterey County, California.”
Many redwoods were destroyed for timber and many to clear land for other purposes, such as roads, agriculture, and development. However, the primary reason for its small native range is the demanding horticultural conditions required by redwoods. They don’t tolerate wind, particularly salty wind from the ocean. They require a lot of water. Where there isn’t enough rain, summer fog compensates for inadequate water. They need well drained soil and plenty of space to grow to their prodigious size of over 200 feet.
Because of these horticultural requirements, there weren’t many redwood trees in the San Francisco Bay Area prior to settlement by Europeans in the 19th century. There were no redwoods in San Francisco where the soil was sandy and strong wind from the ocean is salty. In the East Bay, the pre-settlement redwood forest was less than 5 square miles. (1) In fact, only 2.3% of pre-settlement Oakland was forested and redwoods were a small fraction of the tree cover. (2)
Trying to defy nature
Despite their demanding horticultural requirements and the historical evidence of these limitations, redwoods are often planted where they cannot survive because they are beautiful, popular, and “native” to California. As the climate changes, rising temperatures and drought have killed many of the redwoods that were planted in the past. As the climate continues to change, the future of redwoods in California becomes even more doubtful.
San Francisco’s 2017 Annual Report of the Urban Forestry Council reports that redwoods planted on public land in San Francisco are dying:
“Agencies such as SFO [San Francisco Airport], Zuckerberg General Hospital, and SFSU [San Francisco State University] reported concerns with declining health of redwood trees under their care. This iconic California native tree is not drought tolerant and current research shows that specimens planted in landscape settings outside their native areas are suffering from water restrictions and irrigation with non-potable water throughout the Bay Area. Redwood trees’ water and other cultural needs should be considered when planning future plantings since periods of extreme drought are expected to continue as the climate continues to change.” (page 11)
We see similar examples of planting redwoods in East Bay Regional Parks, where they are dying. Redwoods were planted at Lake Temescal about 5 years ago. Despite the fact that many of them are dead, the Park District continues to plant new redwood saplings adjacent to their dead relatives. Although it is a relatively sheltered area, the trees may have been killed by salty irrigation water.
The growing gap between science and public policy
On March 10, 2018, I attended a conference about resiliency in Davis, California: “Deepening our Roots: Growing Resilient Forests.” I went to hear Greg McPherson speak because I have read many of his scientific publications and I admire his work. McPherson’s research at the US Forest Service about the economic value of ecosystem services provided by urban trees (carbon storage, reduction of energy use for heat/cooling, increased property values, removal of particulate pollution, etc.) has been vital to those who defend our urban forest.
McPherson lives in Davis, where he is conducting a 20-year study about the urban forests of the future, i.e., those that will survive predicted changes in the climate. Three years into the study, his research team has made some preliminary recommendations for the trees that are likely to survive anticipated changes in the climate. None is native to Northern California. Most are foreign, particularly Australian.
McPherson also showed photos of trees being planted now that are destined to die in the near future. One was a densely planted row of redwoods in a median strip in Davis. Professor Arthur Shapiro, who lives in Davis, made this comment when I told him about McPherson’s presentation, “Redwoods are the walking dead here. I’ve known that forever and a year.” McPherson said redwoods have no long-term future in most of California. None of the public land managers in the Bay Area seems to know that.
East Bay Regional Park District ignores reality
East Bay Regional Park District is making a big investment in expanding redwood forests into places where redwoods did not exist in the past and where they are unlikely to survive in the future. They are clear-cutting non-native trees and creating visual screens on the periphery of the clear-cuts by planting redwoods along the trails. This photo was taken in Sibley Volcanic Reserve in March 2018 (the area is larger than shown in this photo):
These are areas that were a part of EBRPD’s “Wildfire Hazard Reduction and Resource Management Plan.” The Fuels Management Prescription for this Recommended Treatment Area was supposed to thin the eucalyptus trees to spacing of 25 feet by removing only small trees with trunks less than 10 inches in diameter. The original plan for this area did not include any replanting of trees.
The recent implementation of this project suggests that EBRPD’s strategy for tree removals has changed. At least in this instance, the trees have been clear-cut, not thinned. And redwoods were planted where none were originally planned.
It is always risky to speculate about the motivations of other people, but I will venture a guess about this new strategy. The Park District’s commitment to destroying non-native trees seems to have escalated from thinning to clear-cutting. And the public’s opposition to the destruction of trees seems to have convinced the Park District that they must plant native trees to replace the trees they have destroyed.
Unfortunately, the Park District does not seem to have taken the changing climate into consideration. The redwoods may survive long enough to placate the public, but they are unlikely to survive in the long-term. It is a good public relations strategy, but not a good strategy for a landscape in transition in a changing climate. It is also not a responsible strategy, given that the carbon stored by the trees being destroyed will contribute to the changing climate and won’t be replaced by dead redwood trees.
(1) Sherwood Burgess, “The Forgotten Redwoods of the East Bay,” California Historical Society Quarterly, March 1951.
(2) Nowak, David, “Historical vegetation change in Oakland and its implications for urban forest management,” Journal of Arboriculture, 19(5): September 1993
Conservation Sense and Nonsense 