A researcher says vast numbers of Southern California trees are dying from insects and disease — an unprecedented die-off that may cost the region billions of dollars and leave it much less green.
Greg McPherson with the U.S. Forest Service says just one species — the polyphagous shot hole borer beetle — could kill 27 million urban trees in Los Angeles and neighboring counties.
That's roughly 38 percent of the 71 million urban trees in the region.
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McPherson says removing and replacing them could cost $36 billion.
He tells the Los Angeles Times the region from Ventura County to the Mexican border is becoming a "post-oasis landscape."
McPherson says trees are struggling with drought, higher salinity levels in recycled water and new pests arriving through global trade and tourism.
"Many of the trees we grow evolved in temperate climates and can't tolerate the stress of drought, water restrictions, higher salinity levels in recycled water, wind and new pests that arrive almost daily via global trade and tourism, local transportation systems, nurseries and the movement of infected firewood," McPherson told The Times.
The loss of the natural green canopy could have consequences for health, property values, carbon storage and air quality, McPherson said.
California live oak, avocado, citrus, ash and prunus species, such as almond and peach trees, are among the most at-risk, according to the U.S. Forest Service research. But many other types of trees, such as California sycamores, also face a threat from the shot hole borer.
"Here's the sad news about sycamores," said Akif Eskalen, a University of California, Riverside plant pathologist. "If we cannot control the shot hole borer, it will kill all the sycamores in California. And when they're done with sycamores, they’ll move to other trees."
Researchers determined the shot hole borer beetle was transmitting a fatal disease to 19 tree species by 2012. The number of identified species threatened by the pest jumped to 30 since then -- and it's likely to increase.
The beetle's origin is unknown, but it might have come from an area around northern Thailand and southern Japan.
The tiny pest, first collected near Los Angeles in 2003, is difficult to control because it reproduces inside trees. It carries a fungus that lines the tunnels they create for eggs and larvae that interferes with the tree's xylem -- the tissue that conducts water.
Adults are brown and black, oval shaped and about the size of a sesame seed. The eggs and lavae found inside the tree are white.
The beetles leave behind tell-tale signs of an attack on the main stem and larger branches. Staining and discoloration are early signs of infestation. Depending on the species of tree, a shot hole borer can also produce a "sugaring" response, identifiable by white mounds of "sugar volcanoes" on the bark.
As for managing the pest, researchers are still trying to determine the best option. Insecticides might reduce attacks and fungicides might limit growth of the damaging fungi, but McPherson told the Times that initial steps should include monitoring the damage and taking steps to remove dead trees. Newly planted trees should include "well-adpated" species, he added.
If residents suspect they have found the polyphagous shot hole borer or seen symptoms in their yards, the Forest Service suggests contacing a pest control advisor, local Forest Health Protection representative, California Avocado Commission or county Agricultural Commissioner office.