Drought In California Turning Deadly For State’s Trees

Laser-imaging technology and satellite data reveal that up to 888 million trees in California experienced measurable canopy water losses between 2011 and 2015.

California’s forests, home to the planet’s oldest, tallest and most-massive trees, are feeling the effects of the state’s recent droughts in the form of progressive water stress, the findings show.

On top of the persistently low rainfall, there has been high temperatures and outbreaks of the destructive bark beetle which increase forest mortality risk.

Getting a big picture understanding of the forests’ responses to the drought, as well as to ongoing changes in climate, demanded more than just a picture of trees that have already died.

The Carnegie Institute’s Greg Asner and his team turned to the laser-guided imaging spectroscopy tools mounted on the Carnegie Airborne Observatory (CAO) to measure the full impact of the drought on California’s forests for the first time. They combined the CAO data with more-traditional satellite data going back to 2011.

“California relies on its forests for water provisioning and carbon storage, as well as timber products, tourism, and recreation, so they are tremendously important ecologically, economically, and culturally,” Asner explains. “The drought put the forests in tremendous peril, a situation that may cause long-term changes in ecosystems that could impact animal habitats and biodiversity.”

water stress

This image shows progressive water stress on California’s forests. Courtesy of Greg Asner

The team’s high tech tools revealed that about 41,000 square miles, or 10.6 million hectares, of forest containing up to 888 million large trees experienced measurable losses of canopy water between 2011 and 2015. Out of this group, up to 58 million large trees reached water loss thresholds that the scientists deemed extremely threatening to long-term forest health.

Given the severity of the situation, even with increased precipitation due to El Nino, if drought conditions reoccur in the near future, the team predicts that there would be substantial changes to already significantly weakened forest structures and systems.

“Our high-resolution mapping approach identifies vulnerable trees and changing landscapes,” Asner added. “Continued airborne and satellite monitoring will enable actions on the ground to mitigate a cascade of negative impacts from forest losses due to drought, as well as aid in monitoring forest recovery if and when the drought subsides.”

The team’s results helped spur the California governor’s recent proclamation of a state of emergency for dead and dying trees across the state.

Top Image courtesy of Greg Asner