Managing Drought in Forest Ecosystems

prescribed-fire
By reducing stand density, prescribed burning can increase resilience to drought and wildfire. New housing developments in and around forested areas complicate the use of fire due to air quality concerns. USFS photo.

More wildfire. More insects and diseases. Less predictable timber supply. Less predictable water supply. Changing wildlife habitat.

Severe drought can cause all of these impacts, and more. USDA Forest Service scientists and partners have created a new resource to help land managers anticipate, prepare for, respond to, and recover from drought.

“Maintaining healthy and diverse forest and rangeland ecosystems is the first line of defense against drought,” says James Vose, senior research ecologist and lead editor of the report. “New drought regimes could overwhelm a forest’s ability to tolerate drought. Today, effective response means integrating drought predictions with on-the-ground practices, coordinating across agencies to reach more stakeholders, and increasing public awareness about the changing face of drought.”

The state-of-the-science report builds on a previous synthesis of drought effects, connecting recent scientific evidence with adaptive practices for managing forests for drought resilience on public and private lands. The report was published as a General Technical Report.

“Taking the long view, this approach can shift land managers away from crisis management and instead make drought planning an integral part of forest management operations,” says Vose.

Drought effects vary across the wide range of U.S. climatic zones, topography, and vegetation types. To meet land managers’ needs, the report includes regional approaches for minimizing drought impacts and facilitating recovery. Regional chapters include Alaska, California, Great Plains, Hawaii and U.S.-Affiliated Pacific Islands, Interior West, Midwest, Northeast, Pacific Northwest, and Southeast.

francis-marion-national-forest
The Southeast chapter includes a case study on the Francis Marion National Forest in South Carolina, where planners and managers integrated drought into new forest management and monitoring plans. Photo by Jennifer Moore Myers, USFS.

In the Southeast, droughts are typically shorter than those in the Midwest and Southwest. They can develop rapidly when warm season rainfall is low or variable, when plants use more water due to higher temperatures, or when there’s a lack of tropical cyclone activity.

“Drought impacts almost every aspect of southeastern forests,” says Steve McNulty, research ecologist, Southeast Regional Climate Hub director, and lead author of the Southeast chapter. “Climate change increases the likelihood for severe droughts, now and into the future.”

Climate change is shifting the Bermuda High westward, closer to southeastern states. “The High traps heat and prevents cold fronts carrying moisture from moving in. This creates parched conditions that can lead to flash droughts and rapid increases in fire risk,” explains McNulty.

How can forest land managers combat drought? Options include:

  • Reducing stocking density through thinning or prescribed fire,
  • Favoring drought-resistant tree species with selective thinning and planting,
  • Reducing invasive species,
  • Increasing water storage to maintain riparian areas and wetlands.

“We know that higher forest leaf area and stand density leads to increased forest water use. We can start to look at reducing stocking density, to create a water buffer. We can think about slightly understocked stands as a new normal, which can help to prevent secondary drought effects like southern pine beetle outbreaks,” says McNulty.

“In fact, we’re restoring pine woodlands and grasslands with this goal in mind. We can consider thinning more than we have in the past. Along with more controlled burning, these practices will help southern forests become more drought and fire adapted.”

There are still unknowns and a role for research on managing forests for drought resilience. “We’re still working to understand how different species use water at broader spatial scales. There are interactions between site conditions like slope and soils. The Southern Research Station’s network of experimental forests is a great framework for evaluating water use by a species across a range of climate and site conditions,” adds McNulty. “We can explore which practices affect soil water levels and try to identify water-conserving forests that are less susceptible to severe drought over the long term.”

Read the full text of Effects of Drought on Forests and Rangelands in the United States: Translating Science into Management Responses.

 For more information, email Steve McNulty at steve.mcnulty@usda.gov or James Vose at james.m.vose@usda.gov.

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