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UC San Francisco drafts rescue for imperiled Mt. Sutro forest

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"The existing forest will not recover on its own."

The Sutro Forest is dying.

Technically, that’s not big news in and of itself. Anywhere you have a large number of trees, some will be dying out. The problem with the 61 acres of mountainside eucalyptus forest adjacent to and in the care of UCSF is that it’s dying at a much faster rate than it should. This is according to an action plan the university published this week.

Roughly 25 percent of the 13,340 or so individual trees in the Mount Sutro Open Space Reserve are now standing dead. Back around the turn of the century, the ratio was at 12 percent. You can probably guess the culprit: Drought years, which not only starved the trees but dried out of the forest, in turn causing aggressive beetle populations to explode.

Former San Francisco mayor Adolph Sutro himself planted the mountain back in 1886, filling it with imported blue gum eucalyptus that shortly did what most new transplants to San Francisco do: decided that it never, ever wanted to leave. The blue gum spread until it became the dominant presence on the mountain.

Back then, it didn’t matter if eucalyptus had to work a little bit harder to thrive in a climate unlike its own, because nature was in the mood to be kind. Not so today; while San Francisco’s average rainfall over the past 21 years is 23 inches annually, only one of the past five years reached that benchmark (2015), and only three of the past ten.

The blue gum is taking it the worst. Of the approximately 370 blue gums on each acre of Mount Sutro, 100 are dead.

"There is abundant evidence to suggest that the existing forest will not recover on its own" reads the report, high in the running for one of the most fundamentally depressing flora-based sentences ever composed. "Essentially no sprouting is taking place," it adds, for a close second.

As far as the report's good news, this is it: The university has a silvicultural plan to pitch for the next 20 years. (Silviculture is the art and science of growing trees. Now you know.) The highlights:

1. Less eucalyptus. It sounds like heresy, but with apologies to the ghost of Mayor Sutro, the draft plan calls for scaling back the blue gum population in favor of more native trees better acclimated to lean years.

2. Manual planting. Since the forest itself is presently mostly incapable of initiating its own birds and bees process, we’re going to have to step in, at least for a few generations.

3. Thin out the forest. No, really. As counterintuitive as it sounds, the best way to save the trees is to bump off some of them. "In some locations, native vegetation benefits from the presence of an overhead tree canopy. In other situations, plants that require full sun would benefit from a lack of canopy," the report explains. The circle of life needs a little push now and then.

The plan is at the proposal phase now, and requires approvals and community meetings before going forward.