Increasing Drought Threatens Almost all U.S. Forests
February 22, 2016 - 2:44 PM
(Photo credit: United States Geological Survey)
Forests nationwide are feeling the heat from increasing drought and
climate change, according to a new study by scientists from 14 research
"Over the last two decades, warming temperatures and variable
precipitation have increased the severity of forest droughts across much
of the continental United States," said James Clark, lead author of the
study and an environmental scientist at Duke University.
Clark and colleagues published their paper today in the journal Global Change Biology.
"While the effects have been most pronounced in the West, our
analysis shows virtually that all U.S. forests are now experiencing
change and are vulnerable to future declines," Clark said.
It's a tall order to predict what these forests will look like in 20 years, the researchers say.
Drought across the U.S. West
Drought-induced forest diebacks (the deaths of entire communities of
trees known as stands), bark beetle infestations, and wildfires are
already occurring on large scales across the West. Many models predict
droughts are likely to become more severe, frequent and prolonged across
much of the U.S.
Evidence is also mounting that climate is changing faster than tree populations can respond.
As conditions become drier and warmer, many tree populations,
especially those in Eastern forests, may not be able to expand into new,
more favorable habitats, fast enough to keep up.
"Most forest research is carried out at local study sites, where
trees are individually catalogued and measured," said Henry Gholz, a
program director in the Division of Environmental Biology at the
National Science Foundation (NSF), which supported the research. "This
approach risks 'missing the forest for the trees.'"
The new results show that changes in both western and eastern U.S.
forests could happen quickly under drier conditions in the future, said
"Prolonged drought affects wildfire risks, species distribution,
forest biodiversity and productivity, and virtually all goods and
services provided by forests," Clark said, "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."
Forests and drought, from A to Z
The new paper addresses this need by providing a comprehensive
overview of current and projected drought effects on forests nationwide,
how they vary by region, and which management practices could help to
partially mitigate adverse effects.
The paper also identifies critical gaps in our knowledge base that
hinder scientists' ability to predict the pace and extent of future
drought effects on forests.
"We currently have a pretty good handle on predicting the impacts of
climate change and drought on individual trees," Clark said. "Ecologists
have identified many of the important differences between species that
explain how they respond differently to drought."
But, he said, uncertainty still exists about what might happen at the
species-wide or stand-wide levels, particularly in Eastern forests.
"These are the scales where we really need reliable predictions so
forest managers can take steps now to help reduce large-scale adverse
Without a stronger basis for understanding how the complex
interactions among trees, species and environmental conditions work at
broader scales, even the most sophisticated current models can provide
only limited guidance, Clark said. "That's where we need to focus our
Major co-authors of the paper are Louis Iverson and Christopher W.
Woodall of the U.S. Forest Service, as well as scientists with the U.S.
Geological Survey, the University of Vermont, the University of
California (UC), Santa Barbara, Sarah Lawrence College, the University
of Michigan, the University of Arizona, Ohio State University, Harvard
Forest, UC Davis, Northern Arizona University and the Swiss Federal
You don't have permmission to comment, or comments have been turned off for this article.