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Plant some trees, cut down a lot more

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A Public Works employee trims a street tree at 23rd and Castro streets. (Sarahbeth Maney/2017 Special to S.F. Examiner)


With great fanfare, Mayor Mark Farrell announced at an Earth Day breakfast last month that San Francisco would plant 2,000 street trees in the next two years to help combat climate change. It’s all part of The City’s commitment to net zero greenhouse gas emission by 2050.

Trees absorb carbon dioxide, the primary greenhouse gas responsible for global warming, as they grow and live. The more trees we have, the less carbon dioxide in the atmosphere. So planting trees is a good way to reduce our carbon footprint.

Farrell’s announcement, however, struck many of us as sadly ironic. While he wants to plant 2,000 street trees, The City’s Recreation and Park Department plans to cut down 18,000 healthy, mature trees, mostly eucalyptus, in city parks simply because they are not native to the Bay Area. Most of the trees targeted (15,000) are in Sharp Park in Pacifica, which is managed by Rec and Park. But 3,400 will be cut down in parks inside The City, nearly half on Mount Davidson.

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The U.S. Forest Service estimates that about one quarter of the accumulated storage of carbon in San Francisco trees are in blue gum eucalyptus, the trees Rec and Park loves to hate. Because trees release their stored carbon back into the environment when they are cut down and rot, Rec and Park’s plan will result in a large increase in greenhouse gases.

If you are concerned about climate change, then targeting this non-native species for destruction is shortsighted and foolish. And it will wipe out any gains in carbon sequestration made by Farrell’s newly planted street trees.

Rec and Park’s rationale for cutting down these trees is that they weren’t here when Europeans settled the area in the 1700s. But our environment is much different now than it was back then. Over the years, the chemistry of the air and soil has changed because of pollution and other human-driven changes.

One reason non-native plants flourish is because they are often better suited to the current conditions than the natives. This mismatch will only get worse as climate and the environment continue to change further and further away from the conditions that existed at the arbitrarily determined date that makes a plant a “native.”

At this point, scientists can only make educated guesses as to which trees are more likely to thrive in the future climate. To maximize future success, they recommend that people plant as wide a variety of trees as possible, both natives and non-natives.

Clearly, that’s what San Francisco should do if we want to ensure that enough trees will survive to effectively sequester carbon in the future. The City should not allow native-plant advocates to veto planting any species.

Those advocates, for example, have convinced UC San Francisco to cut down 6,000 trees, mostly eucalyptus, on Mount Sutro. This action will only compound the greenhouse gas problem in San Francisco.

And then, there are the plans — strongly supported by the Bay Area chapter of the Sierra Club — to cut down hundreds of thousands of non-native trees in the East Bay. In fact, when the East Bay Regional Parks District proposed only removing some of the non-natives, the local Sierra Club sued, demanding 100 percent destruction. The release of all that stored carbon as the trees decompose will make it much harder for the East Bay to address climate change.

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Farrell’s Earth Day announcement said that The City’s June budget would include $4 million to plant the 2,000 street trees. Hopefully, this includes the cost of maintaining them as well. It does little good to plant lots of trees if they are rarely maintained and ultimately die.

Farrell’s plan to plant a few thousand trees is a modest step to reduce greenhouse gas emissions. But it will be pointless if he allows Rec and Park (and UCSF) to cut down tens of thousands of trees just because they’re not native.

Sally Stephens is an animal, park and neighborhood activist who lives in the West of Twin Peaks area.

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