Destroying the Trees of San Francisco

The San Francisco Natural Areas Program (NAP) plans to destroy thousands of trees in San Francisco’s parks.  The Draft Environmental Impact Report (EIR) for NAP’s destructive plan reaches the bizarre conclusion that removing thousands of trees will have no significant impact on the environment.   This conclusion is based on several fictional premises.  In this post we will examine one of those premises:   that all the trees that are removed will be replaced within the natural areas by an equal number of trees that are native to San Francisco.

The EIR supports this fictional premise by falsely reducing the number of trees that will be removed by:

  • Not counting trees less than 15 feet tall, despite the fact that the US Forest Service survey of San Francisco’s urban forest reports that the trunks of most (51.4%) trees in San Francisco are less than 6 inches in diameter at breast height, the functional equivalent of trees less than 15 feet tall.
  • Not counting the hundreds of trees that were destroyed prior to the approval of the NAP management plan at Pine Lake, Lake Merced, Bayview Hill, Glen Canyon parks, etc.
  • Not counting tree removals proposed by the “Maximum Restoration Alternative” which the EIR says is the “Environmentally Superior Alternative.” [ETA: The Planning Department later admitted that this is a mistake in the EIR.  The “Maintenance Alternative” is the “Enviromentally Superior Alterantive.”]

However, even artificially reducing the number of tree removals does not make “one-to-one” replacement a realistic goal.

The natural history of trees in San Francisco

The primary reason why we know that it will not be possible to grow thousands more native trees in the natural areas in San Francisco is that there were few native trees in San Francisco before non-native trees were planted by European settlers in the late 19th century.  San Francisco’s “Urban Forest Plan” which was officially adopted by the Urban Forestry Council in 2006 and approved by the Board of Supervisors describes the origins of San Francisco’s urban forest as follows:

“No forest existed prior to the European settlement of the city and the photographs and written records from that time illustrate a lack of trees…Towards the Pacific Ocean, one saw vast dunes of sand, moving under the constant wind.  While there were oaks and willows along creeks, San Francisco’s urban forest had little or nothing in the way of native tree resources.  The City’s urban forest arose from a brief but intense period of afforestation, which created forests on sand without tree cover.”

San Francisco in 1806 as depicted by artist with von Langsdorff expedition. Bancroft Library

The horticultural reality of trees native to San Francisco

More importantly, the reality is that even if we want to plant more native trees in San Francisco, they will not grow in most places in San Francisco.  We know that for several reasons: 

  • There are few native trees in San Francisco now.  According to the US Forest Service survey of San Francisco’s urban forest only two species of tree native to San Francisco were found in sufficient numbers to be counted in the 194 plots they surveyed:  Coast live oak was reported as .1% (one-tenth of one percent) and California bay laurel 2.1% of the total tree population of 669,000 trees.
  • The city of San Francisco maintains an official list of recommended species of trees for use by the Friends of the Urban Forest and the Department of Public Works.  The most recent list categorizes 27 species of trees as “Species that perform well in many locations in San Francisco.”  There is not a single native tree in that category.  Thirty-six tree species are categorized as “Species that perform well in certain locations with special considerations as noted.”  Only one of these 36 species is native to San Francisco, the Coast live oak and its “special considerations” are described as “uneven performer, prefers heat, wind protection, good drainage.”  The third category is “Species that need further evaluation.”  Only one (Holly leaf cherry) of the 22 species in that category is native to San Francisco. 
  • Finally, where native trees have been planted by NAP to placate neighbors who objected to the removal of the trees in their neighborhood parks, the trees did not survive.

Will NAP plant trees that won’t survive?

Given what we know about the horticultural requirements of the trees that are native to San Francisco, what are we to think of the claim that all non-native trees removed by the Natural Areas Program will be replaced by native trees?  Is there any truth to this claim?  Will native trees be planted that won’t survive?  Or will they just not plant the trees that they claim will be planted?

We turn to the management plan for the Natural Areas Program for the answer to this question.  In fact, the management plan proves that NAP has no intention of planting replacement trees for the thousands of trees they intend to destroy.  The “Urban Forestry Statements” in Appendix F of the management plan contain the long-term plans for the natural areas in which trees will be destroyed.  All but one of these specific plans is some variation of “conversion of some areas of forest to scrub and grasslands.”  The exception is Corona Heights for which the plans are “converted gradually to oak woodland.”  The Corona Heights natural area is 2.4 acres, making it physically impossible to plant thousands of oaks in that location.

NAP plans to destroy 1,600 trees over 15 feet tall on Mt. Davidson and more if the EIR is approved.


Putting the magnitude of the proposed tree removals into perspective

It isn’t easy to confront public policies.  We all have better things to do.  So, before we leave this issue, let’s consider the magnitude of the loss of thousands of trees in San Francisco.  We turn to the survey of San Francisco’s urban forest by the US Forest Service to put the proposed tree removals into perspective:

  • There are only 669,000 trees in San Francisco, with a tree cover of only 11.9% of the land.  Of the 14 cities in the US reported by this survey, only Newark, New Jersey has a smaller tree canopy, covering 11.5% of the land.
  • Most of these trees are small:  51.4% have trunk diameters of less than 6” at breast height.
  • The highest densities of trees are found in San Francisco’s open spaces, such as parks.
  • The trees and shrubs of San Francisco remove 260 tons of air pollutants (CO, NO₂ , O₃, PM₁₀, SO₂) per year
  • The trees of San Francisco now store 196,000 tons of carbon.  Stored carbon is released into the atmosphere when trees are destroyed and as they decay as chips or logs on the ground.
  • In San Francisco, the blue gum eucalyptus stores and sequesters the most carbon (approximately 24.4% of the total accumulated carbon stored and 26.4% of annual rate of carbon sequestered).  Most of the trees that have been destroyed in the past and will be destroyed in the future by NAP are blue gum eucalyptus. 

If you care about the trees of San Francisco, please keep in mind that the public will have an opportunity to comment on the proposal to remove thousands of trees in the city’s parks.  There will be a public hearing on October 6, 2011, and the deadline for submitting a written comment is October 17, 2011*.  Details about how to comment are available here.

*[ETA:  The deadline for written comments has been extended to October 31, 2011, at the request of the Planning Commission.]

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