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Message to UCSF: Do the math!!

February 20, 2013

UCSF has sent an email to its neighbors about its plans for the Sutro forest in which they say, “Contrary to rumors being circulated, there is no plan to cut down 30,000 trees in the Mount Sutro Open Space Reserve, and it is unfortunate that this misinformation continues to spread.”

Our response is, Do the math!!

The Draft Environmental Impact Report (DEIR) claims that the thinned forest will have 62 trees per acre. (DEIR Appendix F) The DEIR arrives at this figure by assuming that each tree will occupy a circle with a radius of 15’. In fact, it is not possible to pack circles into another geometric space, whether it is a bigger circle, a rectangle or a square without wasting space. Therefore, this calculation arrives at a bogus answer which is larger than is physically possible.

We have calculated the number of trees remaining in the thinned forest based on the number of squares in an acre that are 30’ X 30’. Such calculations of tree density are found in books regarding arboriculture, which corroborates that we are using a standard calculation used by the timber industry and the DEIR is not. (1)


43560/900 = trees per acre if 30 feet apart (the proposed plan)


43560/3600 = trees per acre if 60 feet apart (the proposed plan)


Total number of trees existing now on 61 acres (according to UCSF)


46 acres X 740 trees/acre = Number of trees existing in project area


44 acres X 48 trees/acre = thinned forest with 30’ spacing


2 acres (Demo Area #4) X 12 trees/acre = thinned forest with 60’ spacing


Existing Trees – Thinned Forest = Trees Removed in Project Area


Trees Removed/Existing Trees in total forest = Percent of Trees Removed in Total Forest

If UCSF wishes to reduce the number of trees that will be removed by the proposed plan, it can do so by reducing the spacing between the trees or the number of acres to be “thinned.” All other numbers used to arrive at an estimated number of tree removals are straight-forward mathematical calculations based on the information provided by UCSF.

UCSF would be wise to read the DEIR for its project, which says, “Under full-implementation or worst-case implementation of management activities under the proposed project, approximately 60% of all existing trees, including large and small trees, could be removed.” UCSF reports that there are 45,000 trees in the Mount Sutro Reserve presently. Sixty-percent of 45,000 is 27,000 trees. We think UCSF’s estimate of tree removals is just a few thousand trees less than what is actually planned. What are we quibbling about?

Once again, we invite UCSF to revise its proposed project to reduce the number of trees that will be removed.

(1) Ecology and Silviculture of Eucalypt Forests, R.G. Florence, CSIRO, Australia

One Comment leave one →
  1. Don E permalink
    February 22, 2013 8:06 am

    Have you included the acres on the western slope that will not be cut in your calculations?

    Webmaster: I don’t know what you mean by “included.” The entire reserve is 61 acres. Trees will not be removed on 15 acres on the western side of the reserve because the land is too steep and inaccessible.Therefore, the project is on 46 acres. Look at the calculations. Note that the calculations of the number of trees that will be removed are based on 46 acres: 44 acres will have 30 foot spacing between the trees and 2 acres will have 60 foot spacing between the trees.

    Also, the number of trees does not show the size of the trees. Many of the trees are saplings. A Redwood tree 10 feet high does not equal a redwood tree 100 foot high. I have both planted a forest and thinned a forest, granted on a eucalyptus forest, and a 30 foot spacing is appropriate for most large trees for health and growth.

    Webmaster: The documents have many contradictory statements about the size of the trees. Therefore, we have no accurate means of determining the size of the trees. The inventory done by Hort Science in 1999 said the majority of the trees were 12” DBH or less. That was nearly 15 years ago. Presumably the trees are larger now. The “study plots” used to calculate carbon storage for the DEIR claims that 77% of the trees in those plots are 5” DBH or less (assuming that the study plots are the average density of the entire forest which is 740 trees per acre). However, the authors of the Biological Resources chapter of the DEIR report “an average trunk size of single leader trees ranging from 24-42 inches in basal diameter.”

    Finally, if you actually the read the article on which you are commenting, you will note that the DEIR reports the intention to remove “…approximately 60% of all existing trees, including large and small trees…”

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