One by one, the great stately Monterey pines lining Sunset Boulevard have been coming down.
The trees are being felled by pine pitch canker, a fungal infection that first showed up on California’s coast in 1986 and has slowly but surely infected hundreds of thousands of trees — including thousands in San Francisco.
Although the disease is not new, city agencies are seeing more and more trees infected by the disease to the point where they must be cut down, said San Francisco Urban Forestry Council member Carla Short, who is also the urban forester for the San Francisco Department of Public Works.
On Tuesday, the council will meet to discuss the agencies’ concerns about the disease and consider whether San Francisco should have a specific unified policy about how it handles trees infected by the disease.
Pine pitch canker, believed to be transmitted by insects, can infect most pines native to California, but Monterey pines seem particularly susceptible. The fungus causes lesions on the branches, roots and trunks of the trees, slowly constricting water flow to the tree; most trees eventually die.
The disease also has been found to take a steeper toll on trees in San Francisco than on pines in suburban or rural settings, said Chris Geiger, integrated pest management program manager for the Department of Environment.
“It may have something to do with stress on the trees, with all the exhaust and the harsher conditions of a tree sitting along a city street, as opposed to the middle of a forest,” he said.
The City is expected to lose about 25 percent of its pine trees over the next decade, Geiger said.
“In places like the Presidio or Golden Gate Park, where you have these beautiful mature stands of Monterey pines, it’s quite distressing when a bunch of them die and have to be cut down,” he said.
Arborists in both the Presidio and the San Francisco Department of Recreation and Parks have taken matters into their own hands to try to get a handle on the problem. The disease was first discovered in the Presidio in 2000, and the next year, arborists began testing trees for resistance to the disease, said Christi Conforti, Presidio Integrated Pest Management Coordinator.
Of about 100 young trees tested, 20 were unscathed by the disease, so the Presidio began taking cuttings of those trees and growing them. Now, every time a Monterey pine dies, it’s replaced by a young tree resistant to the disease, she said.
The Rec and Park department has begun taking similar measures, said department spokeswoman Lisa Seitz Gruwell.
Pine pitch canker is plaguing trees in The City, leading officials to meet about what to do next.
What it is: Pine pitch canker is a disease of pine trees caused by a fungus. It can infect many pine trees indigenous to California, but Monterey pines are particularly susceptible. It’s believed to be spread by insects.
Symptoms: The fungus causes lesions that can encircle branches, roots or trunks, cutting off water circulation. The tips of infected branches wilt and needles turn yellow, then red.
Mortality: Many trees die after infection, while others partially die but eventually fight off the disease. About 20 percent of Monterey pines appear to be entirely resistant to the disease.
Effect on The City: Trees in San Francisco seem to be more susceptible to the disease than trees in suburban or rural settings. About 25 percent of The City’s pine trees are expected to die in the next decade.
Sources: University of California Integrated Pest Management Program, City of San Francisco