Our Dry, Warm Future may Favor Oaks

Once established, oaks tolerate drought much better than maple, beech, and other mesophytic species. Photo by Paul Wray, Iowa State University, courtesy of Bugwood.org.
Once established, oaks tolerate drought much better than maple, beech, and other mesophytic species. Photo by Paul Wray, Iowa State University, courtesy of Bugwood.org.

Historically, many oak forests across the eastern U.S. experienced frequent low-intensity fires that promoted the establishment and growth of oaks. “However, fire and other disturbances have become less common,” says U.S. Forest Service scientist James Vose. “Red maple, tulip poplar, and other mesophytic, fire-sensitive, and shade-tolerant trees are increasing in many areas of the eastern U.S.”

But what does the future hold? Over the coming decades, changes in fire regimes, climate, and land use will continue to affect forests. However, new climate and disturbance regimes may actually favor oak forests, according to a new synthesis by Vose and Katherine Elliott, a U.S. Forest Service research ecologist. The synthesis was recently published in the journal Fire Ecology.

Changes in precipitation regimes – the pattern and amount of rainfall and other precipitation – appears to be one of the factors favoring mesophytic tree species in eastern forests. Once established, oaks tolerate drought better than many non-oak species that are becoming common in eastern forests, such as maple, beech, willow, blackgum, and others. However, droughts were less common and less severe over most of the 20th century.

Along with a reduction in drought, fire and other disturbances have also become less common. Oaks are fire-tolerant, and although it’s unclear what fire’s future role will be, it will probably play an important role in shaping oak forests. “The combination of climate change, wildfire, and other disturbances could create environmental conditions that favor oaks,” says Vose.

Climate models suggest that through the 21st century, the eastern U.S. will become warmer and have longer rain-free periods. “The combined effect of these changes will probably be increased wildfire risk,” says Vose. “Multiple models converge on the projections that mixed-oak forests in the eastern U.S. will likely experience greater prolonged dry periods, increased wildfire risk, and larger areas burned.”

According to Vose and Elliott, future conditions will likely favor oak forests – with or without management. However, along with climate change and predicted increases in fire risk, land use is expected to change rapidly. Over the next 45 years, up to 40 million acres of land could be newly developed.

Most development is expected to take place at the edges of cities, in the wildland-urban interface. As the landscape becomes more fragmented, there may be fewer opportunities to conduct prescribed burns, even as the predicted hotter and drier conditions cause increased fire risk. Management intervention, such as thinning and prescribed fire, will be critical to protecting neighborhoods and communities from wildfire.

Management can also create forests that are healthier and more resilient. “Management can enable a faster shift to oak dominance,” says Vose. “This, in turn, would create stands more resistant and resilient to future climate stressors.”

Read the full text of the article.

For more information, email James Vose at jvose@fs.fed.us

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