Although some parts of California have recently seen some large storms that helped to relieve a multi-year severe drought, the water table remains low throughout the state and extreme drought conditions still exist in several areas across the state.
New research from the Carnegie Institution for Science has determined that over 888 million California trees have experienced drought-related water losses since 2011, and as many as 58 million trees statewide are currently experiencing severe water loss.
The new study was published in the Proceedings of the National Academy of Sciences this week, comes after a U.S. Forest Service report last spring that highlighted at least 12 million trees that had been killed by the ongoing drought, but did not resolve questions about how many more trees were at risk from water loss.
More on drought damaging California trees
The article highlighted that trees in California were being stressed from multiple sources. Never mind the years of low rainfall, trees in many parts of California have also suffered from high temperatures and outbreaks of the destructive bark beetle, both of which boost mortality risk for trees.
Given the drought and other problems faced by California trees, the scientific community started becoming aware of the need for a large-scale understanding a forest’s responses to the drought. This obviously required more than just data about trees that have already died. A team from the Carnegie Institution for Science, led by Greg Asner, decided a high-tech approach would yield the best results, so they used laser-guided imaging spectroscopy tools aboard on the Carnegie Airborne Observatory to make an assessment of full impact of the drought on California’s forests. The statistical analysis included both the new CAO data with satellite data as far back as 2011.
The new technique revealed a progressive loss of water in California’s forest canopies over the four-year span. Mapping changes in canopy water content tells scientists when trees are under drought stress and greatly aids in predicting which trees are at greatest death and fire risk.
The new airborne imaging tools made it clear that close to 41,000 square miles (10.6 million hectares) of forest containing an estimated 888 million large trees had seen notable losses of canopy water in the four year period between 2011 and 2015. Among this group of California trees, around 58 million large trees had met or exceeded water loss limits that botanists say are a serious threat to the long term health of the trees.
To give you some idea about the seriousness of the situation, even with more rain coming to the West Coast from a strong El Nino this year, if drought conditions come back to the area in the next few years, the team’s models project significant to already quite stressed and weakened forest ecosystems.
Statement from lead researcher Greg Asner
“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 noted in a press release on the new research. “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.”