by Ari Phillips Posted on January 21, 2015 at 10:54 am Updated: January 22, 2015 at 8:54 am]
A group of California scientists published a study this week comparing forest surveys from the 1920s and ’30s to recent U.S. Forest Service data. What they found was not encouraging for the future of the state’s renowned large trees. Published on Tuesday in the journal Proceedings of the National Academy of Sciences, the study found that drought, changes in land use, and fire suppression efforts have caused the number of trees larger than two feet in diameter to decline by 50 percent in a 46,000 square mile area of the state’s forest they surveyed. “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 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.”
With California currently locked in a serious drought, the role of water stress in determining tree size does not bode well for the future. The study does not factor in the four-year drought now underway as the latest census was taken just before it began. Scientists have determined that the impacts of climate change are exacerbating the state’s current drought. Climate models predict that the state and much of the Southwest will continue to get hotter and drier.
“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.”
According to the study, both large tree declines and increased oak dominance are associated with increases in water deficit, “suggesting that water stress may be contributing to changes in forest structure and function across large areas.”…
By Robert Sanders, Media Relations | January 20, 2015
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. Scientists debate the cause of the decline of larger trees, which has been observed in other parts of the world as well, but many suspect that larger trees need more water than smaller trees to withstand droughts and disease.
Co-author David Ackerly, a professor of integrative biology [and Point Blue Board science board member],
said that stressed forests and the loss of large trees could exacerbate the global carbon situation, especially since many are hoping that forests will soak up more and more fossil fuel emissions….“All these records are now brought together in digital form in the EcoEngine, which will allow more people to plumb the data and ask more questions, such as, What about logging? What do the photographic records show?” Kelly said. “We need to remember that there are a lot of valuable collections of data that we can use to make inferences about the future.” Other co-authors are Christopher Dolanc of UC Davis and Alan and Lorraine Flint of the USGS California Water Science Center in Sacramento.