Is UCSF’s Sutro Forest Actually Unhealthy?

The main argument UCSF makes for the plan to remove 30,000 trees is that the forest is unhealthy. But is it? The letter below is from Alma Hecht, a Certified Arborist who evaluated the forest.


Recently, UCSF published its Draft Environmental Impact Report on its plan for the Mount Sutro Open Space Reserve – an area of 61 acres covered by a dense eucalyptus forest over a century old. Ostensibly to improve the health of the forest, UCSF plans to remove 90% of the trees on three-quarters of the forest. Meanwhile, Ruth Gravanis published an article in the Miraloma newsletter that claimed a similar eucalyptus forest on Mount Davidson was headed for “self-destruction.” [We note that Ruth Gravanis, who is on the Environment Commission and a passionate supporter of the SF RPD’s Natural Areas Program, is not an arborist.]

sutro forest

I am a Certified Arborist and in 2010 with Certified Arborist Jocelyn Cohen evaluated Mount Sutro Forest. We saw a thriving forest. Here are some excerpts from our notes:
mossy tree trunk•    Trees were well rooted along hillsides and flat areas.
•    Visual evidence of a naturalized forest is obvious in trees’ calibers that offer insight into age and health. Tree girths range from wide in oldest trees to narrow where the trees are younger, more closely spaced and/or receiving less sunlight.
•     Poor management of the trees as evidenced by hanging branches and fallen/cut limb piles. Some lower branches were pruned; many cuts were improper leaving stubs or flush cuts into the parent stem.
•    Snags (i.e. standing dead trees) were left in place—perhaps by happenstance — providing habitat for wildlife.
•    Swaths of acacias establishing in areas of recent woodland removal for path expansions or other purposes.
•    When thick carpet of forest duff pushed aside, the soil is very moist to several inches down. Yet, in places where paths have been expanded, the ecotope is becoming drier and dustier.
•    Thriving mosses and lichens on rocks and tree-trunks.
•    Epiphytes colonized in branch crotches.
•    In many areas, climbing vines have been cut, generally at five-ten feet, left dry and dangling from branches in thick nets.”

sutro forest pathWe also noted that it had the characteristics of a fog or cloud forest. Again, from our notes: “As is typical in [such] forests, trees are crowded. Branching is high. Understory is deep. Leaves drip.  Some trees are mature and mighty with crowns beyond view. Others are rangy, young and low enough to meet eye-levels. ‘In forest stands or in other mixed plantings, all trees do not grow at the same rate. Over time certain individuals dominate over others.’ (Reference – Arboriculture: Integrated Management of Trees Shrubs and Vines, Richard Harris, Greg Steinke, James Clark and Nelda Matheny, Prentice Hall 2003.)”

As would be expected in a cloud forest, we saw it was drying out where it had been opened up: “In some areas with indiscriminate thinning and removal of trees, the ground is dry (compared with wet conditions through most of the forest and even on the same trail). Those areas also seem to have higher wind velocities. Dry conditions are particularly noticeable at the Rotary Meadow where an existing clearing was replanted into a landscape of native plants.  Significant differences in moisture conditions are visible.”

The forest appeared healthy, and we saw signs of regeneration in forest trees including eucalyptus. UCSFhas suggested that the forest is dying and infested with beetles. Since it’s a living eco-system, a normal amount of insect life can be expected. But there’s no evidence of a unhealthy levels of infestation, or of a moribund woodland. In particular, the eucalyptus snout beetle, mentioned as a threat to the forest, is not known to be present in San Francisco, being more a pest of Southern California eucalypts. And even there, it’s been well-contained with the introduction of a parasitic wasp.

We are also familiar with the forest on Mount Davidson, which has similar conditions. We think the different opinions stem from a fundamental misunderstanding of tree forms in natural,or naturalized, forests. Here criteria for gardens or timber plantations where the objective is to optimize individual trees for aesthetics or lumber is inapplicable. In either of these naturalized forests the trees comprise a whole entity, wherein some trees might flourish, others might die, but are essential to the living whole.

Muir Woods

“Unhealthy” Sutro Forest? No, Muir Woods

Trees in a forest – especially a dense cloud forest – tend to grow high and fast to reach the canopy, and do little branching until they get into the light. This results in trees that  appear spindly and tufted, but in fact are healthy and well adapted to the place in which they are growing. A wet environment like Mount Sutro Cloud Forestor Mount Davidson) can sustain a very high density of trees and vegetation.

In any case, natural forests -and naturalized forests, like these- will “self-thin” – the trees that are unable to get enough nutrients or light will eventually die.  When this happens, it is the weakest trees that eliminate themselves, and the strongest trees that remain. This results in a forest that is best adapted to the conditions in which it grows. Artificial tree removals for arbitrary spacing destroys the forest’s adaptive mechanism. Removing existing trees in these forests will not improve the forest’shealth. In fact it will send the forest into decline destroying a healthy environmental treasure.

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8 Responses to Is UCSF’s Sutro Forest Actually Unhealthy?

  1. Tony Holiday says:

    Good post. Do the people that are in favor of excessive forest-thinning have lots of opportunity to read these as well? Could give them more to think about and make them think more about plans to overdo things if they’d take time to read what others, including arborists, have to say.

  2. M Scott says:

    Interesting post. Although after doing a google search of Alma Hecht I mainly come across information about her as a “landscape designer”. Can you provide any details about Alma’s experience as a forester? Just because someone is a certified arborist doesn’t mean that I would trust their analysis.

    [Webmaster: We don’t think having a professional landscape design business precludes understanding forests and trees, especially from arborists with a long-term involvement with urban forests. Of course, individual readers may decide which analysis they trust.]

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  4. webmaster says:

    In response to questions about the background of these Certified Arborists:

    Alma Hecht’s early forestry experience in the late 1990’s was helping to establish, develop and run the Ongoing Tree Care program at the non-profit Friends of the Urban Forest. She structured many of the City’s 22,000 young street trees, provided education and information to volunteers and neighbors. After completing her Master’s Degree at the Conway School of Landscape Design, among the foremost sustainability programs in the United States, Alma’s work in forestry continued in tandem with her design work. Currently she consults and cares for trees in early development through senescence. Her horticultural expertise is focused on California Natives and climate appropriate immigrants.

    Jocelyn Cohen is a Certified Arborist, and served on the San Francisco Tree Council for many years.

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