"While the effects have been most pronounced in the West, our analysis shows virtually all US forests are now experiencing change and are vulnerable to future declines," says James Clark. (Credit: iStockphoto)

climate change

Drought now threatens virtually all U.S. forests

Forests across America are feeling the heat from increasing drought and climate change.

“Over the last two decades, warming temperatures and variable precipitation have increased the severity of forest droughts across much of the continental United States,” says James S. Clark, lead author of the study and professor of environmental science at Duke University.

“While the effects have been most pronounced in the West, our analysis shows virtually all US forests are now experiencing change and are vulnerable to future declines. Given the high degree of uncertainty in our understanding of how forest species and stands adapt to rapid change, it’s going to be difficult to anticipate the type of forests that will be here in 20 to 40 years.”

Drought-induced forest diebacks, bark beetle infestations, and wildfires are already occurring on large scales across the West, and many models predict droughts are likely to become more severe, frequent, and prolonged across much of the United States.

[Drought can kill trees for years]

There is also mounting evidence that climate is changing faster than tree populations can respond by migrating to new regions. As conditions become drier and warmer, many tree populations, especially those in Eastern forests, may not be able to expand rapidly enough into new, more favorable habitats through seed dispersal or other natural means.

The new paper, published in Global Change Biology, synthesizes findings from hundreds of studies and serves as a summary overview of a full report released earlier this month by the US Department of Agriculture and the US Global Change Research Program as part of the US Forest Service’s National Assessment on the Impacts of Drought on Forests and Rangelands.

“Prolonged drought affects wildfire risks, species distribution, forest biodiversity and productivity, and virtually all goods and services provided by forests, so there is a pressing need to know what is happening now, what might happen in the future, and how we can manage for these changes,” Clark says.

The new report addresses this need by providing a comprehensive overview of current and projected future drought impacts on forests nationwide, how they vary by region, and which management practices could help partially mitigate problems. The paper also identifies critical knowledge gaps that hinder scientists’ ability to predict the pace and extent of future effects.

Source: Duke University

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