Drought Is Killing the Trees at Lake Tahoe

Fir trees are dying in the Lake Tahoe Basin at a quicker rate than in the rest of California.

The trees are perishing in greater numbers and faster than previously seen before, especially near Fallen Leaf Lake and around North Lake Tahoe, Rita Mustatia, forest silviculturist for the Lake Tahoe Basin Management Unit of the U.S. Forest Service, told SFGate.

"Drought and the stress brought on by drought conditions increases the potential for the spread of insects and diseases that can infest, cause damage to or kill trees," Mustatia said.

Lake Tahoe is situated in the Sierra Nevada mountain range, straddling the California-Nevada border. The Lake Tahoe Basin is occupied by a large number of pine and fir tree species including the Jeffrey pine, lodgepole pine, white fir, red fir, sugar pine, ponderosa pine, and western white pine.

Now, it seems like many of these evergreen firs are dying, turning orange. Russet leaves are a clear sign that a tree is on its way out, with the auburn colors of the dying leaves of deciduous trees indicating the onset of fall each year. Evergreens, however, rarely turn orange unless something is going wrong.

Four thousand acres of trees in the Lake Tahoe Basin are affected by mass mortality, according to an aerial survey by the Forest Service in 2021. The survey found that around 70,000 trees are dead in Lake Tahoe, with over a million trees dead across the Tahoe National Forest.

Across the entire state of California, the survey also found that 9.5 million trees had died.

It is thought that the main driver of these deaths is the scorching drought that has gripped the state recently, leading to blisteringly high temperatures, water shortages, wildfires and other extreme weather.

"This prolonged water deficit has had profound impacts on California forests, killing trees outright and predisposing them to insect outbreaks and other damage agents," the survey said.

Additionally, fire suppression in the Sierra Nevadas has caused trees to be increasingly overgrown, meaning that these cramped trees are competing for nutrients and water in the soil, as well as sunlight.

"Our forests are at mortal peril," Hugh Safford, a recently retired Forest Service regional ecologist, told the San Francisco Chronicle earlier this year. "They are absolutely at mortal peril."

Mustatia said that one way to remedy these mass deaths could be by actively thinning the trees.

"An important way to manage the stress brought on by drought is to stay ahead of it by conducting strategic thinning to reduce tree competition for water and nutrients," she told SFGate. "There is also a need to remove trees that are heavily infested with dwarf mistletoe, which will help reduce its spread to other trees."

According to the Forest Service survey, other factors exacerbating the threats to the trees include root rot and dwarf mistletoe, Cytospora fungus, and bark beetles. Root rot and mistletoe are parasitic plants that steal nutrients and water from the host plant, exacerbating the problems caused by drought and overcrowding. Bark beetles burrow through a tree's bark, eating essential layers of tissue used for water and sugar transport inside the tree. Once weakened by a variety of these other factors, Cytospora can then easily infect a tree.

Dead trees also provide excellent kindling for wildfires, which are now expected to be seen nearly year-round in California. While these fires may help with the overcrowding problem in the forests, they are not a welcome phenomenon for the residents of forested California. In a blaze earlier this month in Northern California, two people were killed.

Drought has also had a host of other impacts on nearly every aspect of the climate, both across California, the rest of the United States, and around the world. Lake Mead, the largest reservoir in the U.S., is approaching dead pool levels due to water shortages, while in China, the government is trialing cloud-seeding to geoengineer rain.