Aug. 15 2018 03:50 PM

Drought, climate change and invasive insects have led to millions of dying trees.

Western pine beetle
Darren Blackford, USDA Forest Service, Bugwood.org


California’s trees are in trouble. Even though the drought has been declared officially over for some time, it’s had a long-term impact on the states’ urban and native forests.

According to the U.S. Forest Service, since 2010, an estimated 129 million trees have died in California’s national forests due to climate change, unprecedented drought, wildfires and an out-of-control bark beetle infestation.

The most serious of the pests currently killing the state’s trees are several species of pine beetle. Pine trees, weakened by drought, are highly susceptible to these expanding infestations. While the beetles usually prey on weak trees, they can overwhelm even healthy ones if insect populations are high.

Pine beetle larvae attack the phloem, the vascular tissue in trees, eventually cutting off the flow of nutrients and water to it and reducing the amount of pitch the tree can release to fight the invaders. “When a pine tree is healthy, it can pitch out bark beetles with a copious outflow of sticky sap,” says Rob Gorden, director of urban forestry and business development at Arborjet, Inc. Woburn, Massachusetts.

Under normal conditions, this pitching-out process keeps beetle populations in check. But conditions in California have been anything but normal. The pine trees, weakened by five years of drought, haven’t been able to make enough pitch to drown the insects. The result was a beetle baby boom.

As a result, California now has millions of dead standing and fallen trees. This buildup of fuel adds to the wildfire risk, creating conditions that can be volatile and dangerous, as we’ve seen in Orange County’s Holy Fire, still raging at the time this article was posted. “It is difficult to stop a fire propelled by wind and fueled by dead trees,” says Gorden,

This situation has destroyed many homes and endangered many others. Dead trees are unstable and prone to collapse, increasing risk to people and property, as well as providing fuel that can easily alight from in a wildfire from drifting embers.

Not much can be done about the trees in the forest besides removing the dead ones. But there are ways to prevent the death of trees that are adjacent to homes. Insecticide applied via trunk injection is effective and increases a tree’s chance of survival.

The treatment is best when applied prophylactically rather than after an attack. These treatments, available from Arborjet and other companies, is effective for up to two years. The chemical is applied and sealed inside the trunk of the tree, making it an eco-friendly approach for birds and beneficial insects.