Fires, drought, beetles taking toll on Tahoe forest
Posted: July 11, 2016Source: Nevada Appeal
“We had a better snow pack this year and a better precipitation season in the Tahoe Basin,” said Brian Garrett, urban forest manager for USFS. “But the trees in the forests are still extremely stressed and one season of 100 percent precipitation does not take you out of that condition.”
He said it takes at least two consecutive good winters for the forest to start to recover.
After a good winter, he said there has been little thunderstorm activity.
‘The snowpack melted early and fuels were exposed early,” Garrett said. “We’re getting to the high fire danger level. Weather has been hot and dry and everything is drying out very quickly.”
He said USFS estimated that on the California side of the southern Sierra some 66 million trees have died.
“We’ve never seen this kind of mortality,” he said. “It’s unprecedented.”
Garrett said the situation isn’t nearly that bad in the Tahoe Basin but that they are seeing increased areas of tree mortality.
“All you’ve got to do is stand back and take a look up the hillside,” said John Christopherson, Natural Resources Manager with Nevada Division of Forestry. “You see dead trees and dying trees.”
The result is an increase in bark beetle infestation because weakened trees are much more vulnerable to insect attacks.
Warmer and longer summers along with less precipitation, “really causes the bark beetles population to explode.”
He said instead of reproducing once, maybe twice a season, they reproduce up to five times a season.
“We know we’re at risk if we continue to have drought stress conditions.”
The United State Department of Agricultural says bark beetles are not much larger than a piece of cooked rice.
“Bark beetles survive in trees that are stressed, diseased, or injured; either by human activity or during storms or wildfires,” USDA says. “In many years, more trees are killed by bark beetles than by fire.
“When beetle populations are low, healthy trees often produce enough resinous pitch to drown” and keep the beetles from entering the trees. When trees are “stressed, they may unable to produce sufficient amounts of defensive pitch.”
Garrett said the Tahoe management unit has been through this scenario before — in the last 1980s into the early 1990s. But since then, he said the unit has changed its tactics, doing much more forest thinning and clearing away dead trees.
As a result, he said the forests are in much better condition today, especially near the urban interface.
“Our priority has been protecting communities,” he said. “That’s where we focus our efforts.”
But in the more remote areas away from urban centers, he said many of the trees that died 20-plus years ago, “are still laying up there.” He said the forest service just doesn’t have the capacity or the money to do all that’s needed in those areas.
Garrett said he would take a few thunderstorms if they come with significant moisture. The danger, he said, is dry thunderstorms accompanied by winds. That can result in “thousands of (lightning) strikes.”
“We haven’t seen that this year — yet,” he said.
In the meantime, Garrett said the trees continue to compete for whatever moisture is still in the ground and tree mortality is on the rise.
Christopherson said the worst hit areas on Nevada’s side of the Sierra are the forests lower down the slopes. When there isn’t enough moisture, he said the trees become weakened and susceptible to attack by bark beetles.
Simply put, he said, “there are too many trees vying for a limited amount of moisture.”
Garrett said they will know more after they conduct this summer’s aerial survey of the forests to see exactly how bad the forests are hurting.