Aerial technology measures effects of drought on California forests

Carnegie Airborne Observatory surveys the Sierras from above.
Carnegie Airborne Observatory surveys the Sierras from above. Photo courtesy of Greg Asner

Environmental scientists using new technology to measure the amount of water in tree canopies have found the California drought is having a devastating effect on the state’s forests.

Scientists are flying over forests and using a process called imaging spectroscopy to measure the mass of water in foliage.

“It does start in the southern forest, north of L.A., Los Angeles area, those forests are in really bad shape, extremely drought-stricken, lots of leaflessness, lot of dead trees,” Greg Asner, earth scientist at the Carnegie Institution for Science, told Warren Olney on “Which Way, L.A.?” last week.

Previous estimates put the number of trees affected by the drought at more than 12 million, but Asner’s research suggests it’s 10 times more than that.

Counting dead trees isn’t new. The U.S. Forest Service has been doing it for years in assessing the magnitude of tree death. Comparing that process to what Asner is doing is like comparing “an apple to an orange,” he said.

Instead of flying low over portions of the state’s forests like the Forest Service does, Asner and his Carnegie Airborne Observatory fly over the entirety of the state’s forests looking not only for dead trees, but for those most vulnerable to drought.

California’s weather is only making things worse for the state’s forests and scientists are still trying to assess how big the impact of drought stress is.   

“No matter how we cut it, it’s going to be a pretty high number this year,” Asner said.

North of Los Angeles, in the Sierras, Asner said he’s seeing a very stressed tree canopy. The drought-stricken trees create a trail leading some 350 miles to the Oregon border.   

Even in the coastal northwest, where the trees are able to absorb the humid air, Asner mapped out a “patchy mosaic” of extreme drought stress.      

“You really can’t get away from it anywhere in the state now, but it’s not an even distribution. It’s really patchy out there,” Asner said. “We’re going to lose a lot of trees and other species may move into those new openings that are generated by the loss of some trees and some species. We don’t really know.”  

It’s going to take monitoring over a longer period to determine how the drought would affect the overall makeup of California’s forests, Asner said.

But it’s in the Sierras where scientists are seeing the most change and where they need to focus their attention and conservation efforts, Asner said.

Despite forecaster predictions that this year’s El Niño could bring a significant amount of rain to the Pacific, that still won’t help California’s forests, Asner said.    

“El Nino after a severe drought doesn’t alleviate drought,” Asner said. “What we need is precipitation in the Sierras that’ll provide snowpack.”

And frozen water in the Sierras is at its lowest in 500 years, scientists estimate. Without that snowpack in the water cycle, droughts can last longer and have greater health, environmental and political impacts.    

Asner gave a TED talk in June 2013 describing his aerial observatory, which uses lasers to detect the chemical makeup of a tree canopy and determine its biodiversity and the rate at which vegetation is growing.