Volunteers Comb Topanga to Count Trees

Scott King scrambled up a dirt embankment to examine a lemon tree and then disappeared into a thicket of unidentified foliage just off Horseshoe Drive in the Topanga neighborhood of Fernwood.

His partner, Andrea Shore, sighed. She thumbed the worn pages of her illustrated guide to 79 tree species, leafing past pictures of the Brazilian pepper and the laurel sumac, as she waited for word from King.

First came the faint sound of dry grass crunching beneath work boots. Then King’s voice floated above the shrubbery.

“I think it’s a ginkgo,” he called. “Or it might be a coral. I can’t quite tell from here.”

Such is the enigmatic task facing a volunteer corps of tree counters. Under the direction of the state Resource Conservation District of the Santa Monica Mountains, about 40 volunteers have spent hours this summer inching along Topanga’s narrow mountain roads and venturing into residents’ backyards to document the species, height and health of thousands of trees. The inventory, which will eventually comb through 12,400 acres in the Topanga watershed, is intended to help biologists, firefighters and residents better protect Topanga Canyon from fire.

The data will be used to generate computer models that show how adding or removing certain types of trees will make the canyon safer while preserving its unique ecology, said conservation biologist Rosi Dagit, the project’s director.

The effort is a novel use of computer software designed to analyze urban ecosystems.

“The reality of it is that our vegetation is always going to burn, no matter what we do,” Dagit said. “But the idea is to manage it in such a way that we maximize our safety and that we don’t lose the important benefit of the trees. What we’re trying to do is find a balance, and it’s tough.”

The last time a major fire ravaged this area was in 1993, when flames tore through the western side of Topanga Canyon and Malibu, killing three people and destroying 323 homes.

The blaze was one of several large firestorms that swept through Southern California that year, prompting the Los Angeles County Fire Department to adopt stricter brush clearance rules to reduce the vegetation--”fuel,” in fire parlance--that feeds fires.

In Topanga, where canyon residents prize their rustic surroundings, the new regulations ignited long-smoldering tensions over the competing demands of fire safety, ecology and aesthetics. County firefighters sparked an outcry in the Topanga watershed last summer by recommending that some trees be pruned or removed.

Dagit said she hopes that the massive tree inventory will help Topangans craft a long-term plan for modifying vegetation. The plan could include gradually replacing some highly flammable trees with other species or systematically thinning certain areas to create buffer zones for residential neighborhoods.

Some of the most flammable trees--pines, eucalyptus and acacias--are not native to the area. Certain native trees such as coast live oaks, sycamores and alders are more resistant to fire, Dagit said.

Any attempt to remove trees must be planned carefully, particularly in an area as mountainous as Topanga. Tree roots prevent erosion and provide slope stability. Take them out and, come the winter rains, down slides the slope. Trees also provide other ecological benefits by storing carbon, removing pollution and reducing storm water runoff.

The Resource Conservation District was awarded several grants totaling $34,295 for the project, including a $14,720 forest stewardship grant from the California Department of Forestry and Fire Protection.

First, the district hired a company to take aerial photographs of the Topanga watershed that were scanned into a computer. Then, project supervisor Deborah Low began scouring the images, acre by wooded acre, to identify objects that looked like trees.

The task, which involves staring at a computer screen filled with green blobs, is fraught with individual judgment calls.

“It looks like there’s another little canopy right here,” Low said as she highlighted a digitized tree with a practiced click of her computer mouse. “And this looks like one here. . . . I have no idea what this little green thing is.”

Often, what appears to be one tree on the computer screen turns out to be three or four when viewed at ground level. The volunteers transform the green blobs into precise lists describing the characteristics of each tree.

After the inventory is finished, which Dagit said would take about a year, the data will be fed into the computer to create more accurate maps. Then people will be able to study computer models of each scenario before they remove or plant any trees.

“We can run models to see how a wind-driven fire would go through Topanga Canyon,” said Assistant Fire Chief Stephen Alexander, whose district includes Topanga. “It’ll give us an idea of how to approach fuel reduction.”

Work on the project has been excruciatingly slow. To cover just the 4,000 acres that are near homes will require hundreds of volunteers, Dagit estimated. When they were recruited in April, King and Shore said, they were told the counting would take only a few hours. Four months later, after devoting about one night a week to the project, they are still at it.

Dagit said King and Shore’s section of Fernwood, which was about 10 acres, was too big. In the future, volunteers will be assigned two acres or less.

“It’s kind of fun, actually,” said Shore, who moved to Topanga this year and said she has enjoyed learning about the trees.

“I never knew that that’s the California pepper tree or that’s a California live oak. So now I’m, like, driving around the 101 and I say, ‘Oh, there’s a pepper tree.’ ”