California has more than 100 million dead trees in its forests, and there is no consensus on their impact on the environment or how to deal with them.
In November, the U.S. Forest Service said an aerial survey revealed that 36 million additional trees had died in the midst of a multi-year drought, bringing the total since 2010 to more than 102 million.
The tree deaths have been concentrated in the southern and central Sierra Nevada, but experts warn of increasing deaths in forests all the way up to the Oregon border.
“The scope and magnitude of the problem is seemingly overwhelming,” said Janet Upton, a deputy director for the California Department of Forestry and Fire Protection (CAL FIRE).
The phenomenon raises questions on what causes wildfires as well as the role that wildfires play in the greater ecological scheme. Officials are also grappling with logistical, financial and public safety risks associated with the removal of the trees.
According to AccuWeather Senior Meteorologist Brett Anderson, five years of drought in California has been the primary cause of the tree deaths. While a series of potent storms in early 2017 has alleviated the dry conditions, it has not been enough to undo the damage to the trees or to prevent the die-off from continuing.
“When you have severe droughts, trees are going to die,” said Adrian Das, an ecologist with the U.S. Geological Survey.
The drought and the resulting tree deaths are byproducts of global climate change, Anderson and Das said.
“The fact that temperatures are warming means that the effects of the drought are probably exacerbated,” Das said.
If the tree population continues to thin out, Anderson said, California will face increased risks of erosion, mudslides and flooding due to the loss of natural barriers.
“These long-term droughts are more likely to be common over the next decade,” he added.
According to some experts, the dead trees pose a major fire threat. When a lot of dead fuel remains on the ground, Upton said, fires burn hotter and damage the soil.
Not everyone agrees that dead trees increase the risk of wildfire. Dick Hutto, a professor emeritus of ecology at the University of Montana, said that large wildfires are almost always caused by dry weather.
“If you’re worried about fire, it’s the weather you’ve got to be worried about,” he said.
While people commonly think of wildfire as a destructive force, Hutto said, it actually serves a greater good in the ecosystem. Many plant species evolve in direct response to it; for example, morel mushrooms emerge and pine cones open after a wildfire.
In addition to drought, California's trees have been weakened by bark beetles.
“A lot of trees are dead from infestation,” said AccuWeather Senior Meterologist Ken Clark.
According to CAL FIRE, bark beetles attack stressed trees by boring holes into the bark. A healthy tree would be able to fend off attack by exuding pitch (a substance derived from the sap of coniferous trees) into the holes, pushing the beetle out. However, drought-stressed trees have a difficult time producing enough pitch to fight off insects.
“Over five years of drought has robbed trees of their normal ability to protect themselves from bark beetles,” Upton said. “There’s barely enough water to keep trees alive.”
While bark beetles have been destructive to trees, she conceded that there have only been a couple of fires in beetle-infested areas.
Although Hutto said he doesn’t support harvesting dead trees indiscriminately since it could disturb ecosystems, he and other experts agree that dead trees in populated areas pose major risks. That means removing trees that endanger people, homes, buildings and infrastructure, such as power lines.
While there is “zero chance of removing 100 million dead trees,” Upton said, California state officials are honing in on “10 high-hazard counties.” A Tree Mortality Task Force has been formed that includes over 80 local and state governmental organizations, including the California Department of Transportation.
The task force has so far removed about 423,000 trees, Upton said. In addition, the state government has provided about $15 million in funds to help communities deal with dead trees on a local level.
The state has also allocated about $6 million worth of equipment such as wood chippers, saw mills and air curtain burners (which mitigate smoke from open fire burning) to local governments to deal with dead trees.
California residents who face risks from wildfires and dead trees can learn about how to protect themselves and their property at CAL FIRE's website.