A catastrophic forest die-off in California’s Sierra Nevada mountain range in 2015-2016 was caused by the inability of trees to reach diminishing supplies of subsurface water following years of severe drought and abnormally warm temperatures. That’s the conclusion by researchers from the University of California, Irvine and UC Merced outlined in a study published today in Nature Geoscience.
“In California’s mixed-conifer mountain forests, roots extend from five to 15 meters deep, giving trees access to deep-soil water,” said co-author Michael Goulden, UCI professor of Earth system science. “This is what has historically protected trees against even the worst multi-year droughts.”
But Goulden said the severity of California’s 2012-2015 dry-spell exceeded this safety margin. Many forest stands exhausted accessible subsurface moisture, leading to widespread tree death.
From 2012 to 2015 the entire state of California experienced a crippling drought, and it was especially severe in the southern Sierra Nevada. With a multi-year combination of below-average precipitation and above-average warmth, the resulting drought was considered to be the most extreme in hundreds of years.
Observations by the U.S. Forest Service Aerial Detection Survey showed that many tree stands suffered nearly complete losses of mature conifers. Pines were especially hard hit, due to an infestation of bark beetles. A post-drought survey found that the tree mortality was greatest at lower elevations, with nearly 80 percent loss in 2016 compared to 2010.
Read more at: University of California - Riverside
A massive tree die-off struck California's Sierra Nevada mountain range at the end of the 2012-2015 drought. Numerous stands, such as the one near Soaproot Saddle (pictured), suffered significant losses caused by the exhaustion of soil water supplies tapped by the trees' deep roots, a recent UCI, UC Merced study concluded. (Photo credit: Margot Wholey / UC Merced)