Blackberry habitat, 2010

Around this time last year, Sutro Forest was alive with birdsong all day from dawn to late dusk.

“We walked up into the Sutro Forest on a peaceful bird-filled evening,” we wrote  in late February 2010. “A few outside noises drifted in. The trees were full of the tweets and trills of bird-sounds…”

Today, it wasn’t. Down in the Interior Greenbelt, the winter wrens still sang, but not as many or as loudly as last year. That’s where the Kill-Trees trail-work has felled dozens of trees and stripped out a great deal of understory. The South Ridge, incessantly song-filled last year, was even quieter with just an occasional chirp or tweet.

photo credit: 123rf.com

Himalayan Blackberry is a plant that nativists love to hate. It grows quickly and persistently and forms dense thorny thickets, practically impassable. But… blackberry is brilliant habitat for birds, animals and insects. It provides great cover, and a wonderful place to hide. Insects eat the leaves, or stop by at its pale pink flowers for nectar. Some lay their eggs on the leaves and stems. For small animals, it’s a place to hide from predators. For birds, it’s a place to safely nest.

And the nesting season has started in San Francisco. Bird-watchers already report nesting activity: nest building, stick-carrying, even egg-laying. Many birds are territorial, and some of the birdsong we hear is from males staking out their ‘turf.’ If this ‘turf’ is much reduced, many will not find territories or mates.

Habitat destruction, 2011

As we said in our post describing the Sutro Forest’s ecosystem, “A single blackberry thicket can provide a great deal of habitat. Consider one that’s say 8 feet by 10 feet and 6-7 feet tall  (about as high as a person — the normal height for blackberry to grow unless it’s mown down). That’s over 500 cubic feet of habitat for insects and birds. The same thicket, mown down to 1 foot high, will only provide 80 cubic feet of habitat. And it’s much inferior habitat because it offers a lot less protection — it’s flatter and more visible. ” It may also become unsuitable as a nesting site, being not only more visible but low enough to be within easy reach of predators.

That’s what’s happening to the forest now. Most of the thickets have been mowed down. Trails that were perhaps five feet wide with walls of bushes on either side are now maybe fifteen feet of mowed-down ground. The forest is visibly thinner than it was before. The amount of habitat has been sharply reduced.  The two forest pictures here show the same trail, in August 2010 and in February 2011.

TAMING THE WILD FOREST

Each month — and sometimes more often — the Sutro Stewards gather volunteers. (The Sutro Stewards — formerly the Mount Sutro Stewards — are an organization active on the mountain, with UCSF’s support.)  Sometimes they work in the Native Garden; they have a project underway now to replant a meadow with plants attractive to “native pollinators.” In this, we hope they succeed. A lot of time, effort and money has gone into the garden: over $100,000 (mostly from Rotary, and, recently from the SF Parks Trust); and hundreds of volunteer hours if not more. We would like to see their efforts pay off in terms of more butterflies and birds; so far, the Native Garden has not appeared particularly rich in wildlife.

But they’re also mowing down the forest’s understory, pushing down dead stumps, taming the wildness of this naturalized forest. Many of the places that were dense woodlands only six months ago are much more open now.

Nesting in blackberry – Photo Credit: 123rtf.com

SILENT SPRING

The forest has (or had) over 40 species of birds (listed here and here). The small songbirds need places to hide, and love the bushes. The woodpeckers and sapsuckers like the dead or dying stumps of trees, some of which are riddled with delicious insects.

We haven’t heard the Great Horned Owls this year, either. Are they still around?  We don’t know.

Also lost is the sense of seclusion that existed until only months ago. Inside the forest, the city vanished. Its sounds disappeared. It was another world, green and lush and full of birdlife, a canopy of trees overhead stretching into the sky.  Only occasional “portholes” through the foliage showed views toward the ocean or Golden Gate Park. Now, the city is visible everywhere along the outer trails. The forest still stands majestic and beautiful, but the other-worldly feeling is diminished.

Can the forest recover? We believe it can, with the regrowth of the blackberry so the trails are actually trails instead of highways through the forest, with the regeneration of plants amid the trees so ground now covered in ivy and barkstrips is once more lush with bushes. But first, the Sutro Stewards would have to stop destroying habitat.

(Bird photos from 123RF Stock Photos used under license. For other pictures of birds’ nests in blackberry bushes, see here for a catbird nest, here  for a song-sparrow nest, and here for a picture of an Anna’s hummingbird nest attached to a blackberry bush, taken in San Francisco by ace photographer Robert Clay. The last two images are commercially available at the sites linked.)

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