State Forests Seeing More Tree Mortality

Posted by on Jul 7th, 2016 and filed under News. You can follow any responses to this entry through the RSS 2.0. You can skip to the end and leave a response. Pinging is currently not allowed.

Photo courtesy of USFS Tree mortality seen at Bass Lake, Sierra National Forest.

Photo courtesy of USFS
Tree mortality seen at Bass Lake, Sierra National Forest.


The drought affects all residents of California – humans, pets, wild animals and especially plants. The biggest plants in Southern California that need the most water are trees, like the conifers and oaks in local neighborhoods and in Angeles National Forest. And now, as a new study finds, they are dying in droves.

“We’ve seen a major increase in tree mortality across California’s forests. Not just [in the land controlled by] Forest Service, because we do [survey] other lands out there, but basically in 2014 we had 3.3 million dead trees. In 2015 it jumped up to 29 million,” said John Heil, press officer for the Pacific Southwest region of the U.S. Forest Service. “We typically do 150 aerial surveys each year when we go out and fly over [the area] with some really good [equipment] when they measure the number of trees across the landscape.”

The aerial surveys are done in conjunction with the Jet Propulsion Laboratory in Pasadena using NASA’s Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) aboard an ER-2 aircraft. AVIRIS gathers spectroscopy data and, combined with human operators using oblique viewing angles, color and texture, healthy trees are distinguished from sick or dying trees. Various species can also be identified.

The first flight of 2016 took place in May and examined the hardest hit area of tree mortality in Sequoia, Sierra and Stanislaus national forests in the central and southern Sierra Nevada range. In that one area’s flight, 26 million dead trees were found – 89% of 2015’s total, and there are still 149 flights left remaining this year. The next flight took place yesterday, Wednesday, but the data is not yet available.

Bore holes are evidence of bark beetles, which attack trees already stressed due to drought conditions.

Bore holes are evidence of bark beetles, which attack trees already stressed due to drought conditions.

Two flights conducted last year observed the Crescenta Valley’s resident forest, the Angeles National Forest. One flight took place from April 8-10 and another Aug. 10-14. The April flight surveyed more than 4.2 million acres, covering the Cleveland, San Bernardino, Angeles and Los Padres national forests, Pinnacles National Monument and nearby private lands. It was discovered that 164,000 acres had notable tree mortality with 2 million dead trees. Live oaks in Angeles, east of Santa Clarita, were hit particularly hard. The August flight saw a jump in mortality. The flight surveyed 6.24 million acres, primarily of the Cleveland, Angeles, San Bernardino national forests and portions of Los Padres, Sequoia and Inyo national forests. Of that total, 854,000 acres had noticeable mortality, and there were 11.75 million dead trees.

The trees are dying not only from lack of water but from lack of defenses. Bark beetles are abundant and thrive in warm temperatures. They are usually killed off in a harsh winter, but the last two years have seen rather mild winters, so their numbers have increased. Add to that the warm summer and their population explodes, overwhelming the already taxed trees.

“We’re in our fifth year of drought,” Heil said. “What happens in a drought is that the trees’ mechanisms for defense become weakened from the lack of water and the bark beetles attack the trees. So the bark beetles are thriving and a lot of these trees are dying as a result. If they’re not dying from the drought already, they are dying from the attack.”

Wildfires pose another danger to trees. With trees being as dry as they are and with other dead trees still upright in the stand, throwing their needles down to coat the forest floor, wildfires are at high risk. The dead trees, thoroughly killed and structurally weakened by the bark beetles, have a tendency to fall over. This adds more fuel for fires and increases the severity and intensity of the blaze, said Stanton Florea, fire information officer with the U.S. Forest Service. It is now the height of the fire season, and there have been some wildfires already. In addition to the wildfires, there are human created fires that spread and become brushfires across the overly dry chaparral around Los Angeles. These can easily spread out of control quickly in wooded areas full of dead, beetle-eaten fuel. As of press time, fire crews are battling the Sierra Fire at Sierra Highway and Newhall Avenue in Santa Clarita. L.A. County Fire Dept. expects it to be knocked down quickly, but it has already consumed two acres as it burns on both sides of Sierra Highway.

One would think that the coming monsoons of August and September may bring rain and reduce the fire threat but, as Florea said, they also bring lightning strikes that create lightning fires. It is a long uphill battle for the forests of California, and the USFS has partnered with CAL Fire and several other agencies to create a Tree Task Force that will help in the fight. As for the plans going forward for USFS itself, the immediate solution is to make the forest healthy again through thinning, focusing first and foremost on the areas which are frequented by employees and visitors to the forests.

“One of the things we need to do, [and that] we’re looking to do more of, is to do more thinning to reduce the overcrowded stands of trees,” Heil said. “What it’ll do is create a healthy, resilient forest that can handle the disturbances from drought, bark beetle attacks and wildfires. If there aren’t as many trees competing for that water, the trees that are left will be more healthy and able to handle and withstand these attacks.”

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