Warmer, drier climate altering forests throughout California

Historical California vegetation data that more than once dodged the dumpster have now proved their true value, documenting that a changing forest structure seen in the Sierra Nevada has actually happened statewide over the past 90 years. A team of scientists from the University of California, Berkeley, UC Davis and the U.S. Geological Survey compared unique forest surveys collected by UC Berkeley alumnus Albert Wieslander in the 1920s and ’30s with recent U.S. Forest Service data to show that the decline of large trees and increase in the density of smaller trees is not unique to the state’s mountains. “Older, larger trees are declining because of disease, drought, logging and other factors, but what stands out is that this decline is statewide,” said study leader Patrick McIntyre, who began the research while a postdoctoral fellow at UC Berkeley and now manages biodiversity data for the California Department of Fish and Wildlife. “Forests are becoming dominated by smaller, more densely packed trees, and oaks are becoming more dominant as pines decline.” The authors found that the density of large trees declined in all regions of California, with declines up to 50 percent in the Sierra Nevada highlands, the south and central coast ranges and Northern California. “Based on our data, water stress helps to explain the decline of large trees,” McIntyre said. “Areas experiencing declines in large-tree density also experienced increased water stress since the 1930s.” The increased density of smaller trees is usually attributed to fire suppression statewide, he noted...more