Nearly 80,000 trees throughout San Diego County have died as result of a beetle infestation that has spanned a decade in parts of Southern California, according to researchers at the University of California in Riverside.
On Saturday, researchers identified the beetle, referred to as the goldspotted oak borer, as a major threat to coast live oaks, California black oaks and canyon live oaks.
Using a $635,000 federal grant, UCR natural resource specialist Tom Scott and UCR Agricultural and Natural Resources researcher Kevin Turner studied the oak borer and discovered that firewood shipments are most likely the leading cause of the pest's propagation.
"If we can keep firewood from moving out of the region, we may be able to stop one of the biggest invasive pests to reach California in a long time," said Scott.
Oak borers emanated from Arizona, likely being carried across the desert into California by firewood importers in the mid-1990s, according to researchers. The towns of Descanso and Guatay in the Cleveland National Forest, about 40 miles east of San Diego, were the first devastated by the beetles, which have infested virtually every oak tree in the locations.
Known for burrowing into the timber and feeding on its cambium, the beetles have a reputation for damaging oaks' water- and food-conducting tissues. The creatures leave distinct D-shaped holes in the bark when they chew their way out, according to the researchers.
Researchers said about 10 million acres of red oak woodlands in California are threatened by the species.
Scott and Turner found that the pattern of oak borer outbreaks points to firewood as the means by which the beetles are spreading throughout the region. Communities that harvest their own firewood are largely unaffected by the pests, the researchers said.
Trees more than two centuries old have been felled by the creatures.
In parts of the Cleveland National Forest, artificial canopies have been installed for campers because the natural shading is gone as a result of oak borer activity.
Adding to the issue is the cost of removing massive dead or dying oak trees, which can cost anywhere from $700 to $10,000, according to UCR.
"Quarantines don't work, but enlightened self-interest can keep oak woodland residents from importing infested firewood," Scott said. "This is a situation where the university can play a critical role in changing behavior through research and education rather than regulation."