Tahoe Tree Mortality Increases in 2017
Despite last year's wet winter, the Lake Tahoe forest saw an increase in tree mortality.
Last winter's record snowpack appears to be having a positive impact on the amount of trees that died this year in the Sierra Nevada. In fact, California saw a decrease in tree deaths from 62 million in 2016, to 27 million in 2017.
"Possibly, what we've seen is there could be some recovery in just one year after a drought, given the water year that we had last year," Patricia Maloney, Associate Director of the Tahoe Environmental Research Center said.
Other studies show that it could take one to three years for trees to recover from a drought. That might be what is happening in the Tahoe Basin. Despite a snowpack that was double the average, Lake Tahoe's tree mortality rate increased this year. In the last decade, 304,000 trees have died on 40,000 acres managed by the U.S. Forest Service Lake Tahoe Basin Management Unit. 168,000 of those died in 2017, up from 72,000 in 2016. In fact, only 6,000 trees died in the Tahoe Basin in 2014. Four years of drought made many trees more susceptible to bark beetle infestations.
"You have those sort of dry, drought-stressed trees and you create conditions that are favorable for those kind of outbreaks to occur," Maloney said.
Maloney says healthy trees produce sap that fends off bark beetles, but that is harder to do without enough water.
"They're able to overwhelm them and kill those trees," Maloney said.
Most of Tahoe's tree deaths are on south-facing slopes on the north shore of the lake. Despite the higher number of tree deaths, Maloney says she can see a difference in the forest. Many rust-colored pine needles are turning green again, thanks to more water in the soil. Still, many dead trees remain, creating potential safety hazards and fire danger.
"Standing dead and down dead trees are like match sticks in a forest," Maloney said.
Trees help stabilize the soil and clean the air. Trees have adapted to the arid climate but Maloney says fire suppression efforts have made some forests unhealthy.
"By suppressing fires, we've increased our stand densities, and so in those areas where you have overstocked forests, they are set up for a bark beetle outbreak," Maloney said.
Federal and state agencies continue to thin forests of dead trees and underbrush. Maloney says that is helping tree mortality rates from climbing even higher.
"I think the agencies have done a really good job in mitigating it across all of the Tahoe Basin," Maloney said. "It could be a lot worse."
The Tahoe Fund and California Tahoe Conservancy are growing 10,000 sugar pine seedlings. When the plants are mature enough, they will use them to reforest some areas of the Tahoe Basin.