Glen Canyon Trees: Decoding the Arborist’s Reports

In September 2012, we published our analysis of the tree-felling expected in Glen Canyon. A new arborists’ report dated October 1, 2012 changes the numbers.  It now recommends cutting down nearly 150 trees – still a lot, but an improvement on the 279 earlier recommended.

Back in September, in the first project (playground, tennis court, grand entrance, restroom and Rec Center heating) they expected to cut down 68-70 trees (after initially talking of 10 or 11 trees). According to a statement by Dennis Kern, 10 were in the way of the project, and 60 were hazardous. According to the Arborists’ Report (dated March 2012) only one of the trees was actually hazardous, and another 14 were dead or dying. The others were being removed because of “poor suitability.


When they actually announced the start of work, they revealed that the plan was to fell 58 trees. This is different from the 68-70 proposed earlier, and we wondered why. Tree felling could have started any day after October 15th, last Monday. However, a tree-loving neighbor appealed the project, and it will be delayed for some weeks until that appeal is resolved.

So what’s tagged for felling now (for this project)?

  • 6 trees that will be impacted by the project (Tag numbers 62, 63, 64, 65, 68, and 70). Five of the trees, earlier marked “maybe remove?” are now certainly on the chopping block. This includes the gracious old eucalyptus at the entrance from Elk St.
  • 1 tree (eucalyptus tagged #9) with a risk-rating  of 9  (on a 4-12 scale where 3 is best and 12 is the worst).
  • 7 trees with a risk-rating  of  8 (tag numbers 3, 11, 28, 41, 55, 59, and 170).
  • 43 trees with “poor suitability.”

That’s 57 trees. (Why it’s not 58, we don’t know exactly.)


Meanwhile, we obtained a new edition of the Arborist’s report, this one dated October 1, 2012. This report is a reworking of the March report, still covering 627 total trees evaluated. However, it now includes an actual hazard rating for each tree.

  • Fell 117 trees, not 247.  It recommends felling 58 in the project area; and another 59 trees elsewhere in the park, for a total of 117 trees. This is a lot better than the original recommendation, which was to remove 190 trees in the project area and another 57 elsewhere in the park – 247 trees. (SF RPD did not actually decide to remove 190 trees in the project area; the 70 trees were some subset of that.)
  • Fewer trees in the Project Zone. The most important change in the report’s new edition is that they reduced the number of trees defined as being inside the project area: it’s now 147 of the 627 trees instead of  250 of the 627 trees as in the March report. Three of the original trees are already gone, so that’s a difference of 100 trees.
  • They’re not all the same trees as before. Some trees originally recommended for preserving are now to be removed, and vice versa. We haven’t understood the reasons in most cases. We’re still asking SFRPD for a walk-through and explanation.
  • Among those to be “preserved” is the bee-hive tree, a Monterey pine (tag #38).  Though it was earlier said to be hazardous, it only has a risk rating of 7.


The arborists evaluate each tree on three criteria:

  • Failure potential (how likely is the tree to fall or drop a branch);
  • Size of the falling part;
  • Importance of the target (if it fell, what would it damage?)

For each criterion, they score the tree on a scale of 1 to 4 (best to worst). Then they add up the scores, which gives a Risk scale of 3-12, where 3 is the best and 12 the worst.

A small young tree in a forest would probably score a 3. A big diseased tree near a school might score a 12. Most trees score between 5 and 8. A score of 9 is the City’s threshold for action; it will remove or prune the tree. A score of 8 is more of a gray area.


We don’t know what this means for the excluded trees: are they saved? Or will they fell them in a separate project, one of the many that are scheduled to remake the Canyon? Other tree removals likely:

  • The Significant Natural Areas Management Plan calls for cutting down another 120 trees; that is expected to go into effect in 2013 or 2014 if the Environmental Impact Review is okayed.
  • Any tree under 15 feet tall can be removed without notice for any reason.
  • As of now, our best estimate for the number of trees to be felled exceeds 300 trees.

As the number of trees affected by Glen Canyon Park’s makeover fluctuates, we will try to follow and report on the projected numbers.


The SF RPD has written about planting 163 trees in Glen Canyon Park. We have a planting plan dated May 2012. It only lists 116 “trees” –  a classification in which it includes bushes (for example, flannel-bush and red-flowering currant) and vegetation USDA describes as “shrubs or small trees.”  Less than a third of the saplings will grow to be over 40 feet tall in the next 25 years.  (We’ll get back to that in another post.) [Edited to Add: We did, HERE.]

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