Are California's Forests Changing With the Climate?

You've likely heard all about how climate change is impacting our forests, changing how fast they grow, and which species grow fastest. Now, new research has revealed that a warming clime is even impacting forests in California, where a statewide change in tree species and density has been occurring for nearly a century.

That's at least according to a study recently published in the journal Proceedings of the National Academy of Sciences, which details how California's largest tree species (mainly pines) are slowly disappearing, even while smaller trees (lesser oaks) move in and increase in density per forest.

Study leader Patrick McIntyre quickly admitted in a recent statement that this trend is not exactly unusual. It is often part of the incredibly long and slow natural cycles of forests, in which the mightiest must fall only to return in several decades.

"Older, larger trees are declining because of disease, drought, logging and other factors," McIntyre said, "but what stands out is that this decline is statewide."

What's more, the change is occurring at the same pace in a great deal of California's forests, over the last nine decades, according to data from the US Forest Service and flora surveys taken by researchers at the University of California, Berkeley.(Scroll to read on...)

McIntyre and his colleagues 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."

And while water stress is not exactly uncommon in a part of North America that commonly sees drought conditions, the researchers say that the situation has increasingly worsened over the last 90 years. Rising temperatures, they wrote, may be exacerbating the problem, with dying big trees releasing the carbon dioxide (a greenhouse gas) they normally absorb in photosynthesis.

"There's no question that if you are losing large trees, you are losing the standing carbon in the forest," co-author David Ackerly added. "Loss of these big trees and the impact of drought stress become a big concern going forward in terms of its impact on the carbon cycle; they can turn a carbon sink into a source of carbon released to the atmosphere."

And that theory may not be entirely wrong, After all, 2014 was recently confirmed by three separate international climate authorities as the hottest year ever recorded, continuing a trend in near-constant net warming across the globe since the 1890s.

Reason for Doubt

Still, a little skepticism could be healthy. Just last October, researchers from the US Department of Agriculture and Pennsylvania State University's Department of Ecosystem Science and Management revealed that the decline of pines and firs on the other side of the continental US (northeastern woods) may have a lot more to do with a natural "rebalancing" that is unrelated to temperature change. (Scroll to read on...)

"Over the last 50 years, most environmental science has focused on the impact of climate change. In some systems, however, climate change impacts have not been as profound as in others," forest ecology expert Marc Abrams explained in a statement. "This includes the forest composition of the eastern US."

"Looking at the historical development of Eastern forests, the results of the change in types of disturbances - both natural and man-caused - are much more significant than any change in climate," he said.

According to the researcher, there is a great deal of evidence that indicates that, prior to major settlement, North America's forests looked a lot more like the forests they are becoming, rather than the forests they are now.

The same may hold true for California's forests. However, that still needs to be investigated, and Abrams is quick to add that this does not mean climate change isn't happening.

Likewise, when the NOAA recently revealed that the historically harsh four-year drought that is currently pressing on California is not a consequence of man-driven climate change, they pressed that this simply means that efforts to predict and understand climate consequence need to be aimed elsewhere.

"[Other factors] often trumped or negated the impacts of our warming climate, and this needs greater recognition in climate change discussions, scenarios and model interpretations," Abrams added.

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