Mongabay Series: Global Forests

Scientists blame Smokey Bear for making U.S. forests less resilient

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A new study warns that decades of fire suppression have made eastern U.S. forests more vulnerable to climate change.

Scientists blame Smokey Bear for making U.S. forests less resilient
  • Strict anti-fire policy was implemented in the 1940s aimed at stomping out wildfires and preventing them from starting.
  • But many scientists and wildlife experts say fire suppression can be harmful to ecosystems.
  • A new study finds fire suppression has contributed to a big compositional change in eastern U.S. forests, with less resilient tree species supplanting drought- and fire-resistant species.

According to a new study, strict wildfire control has changed the forests in the eastern U.S. over the past century, leading to less drought resistance. Researchers are warning this could make them more vulnerable to the effects of climate change.

Wildfire was a common visitor to many eastern U.S. forests for millennia, encouraging the growth of vegetation species that evolved to survive periodic burning events. But then heavy logging began 140 years ago, spurred by the industrialization of the U.S. and followed by a spate of fires that destroyed much of the region’s remaining forest. As a result, strict anti-fire policy was implemented in the 1940s aimed at stomping out wildfires and preventing them from starting.

The iconic Smokey Bear became the mascot of movement, and “Only you can prevent forest fires” became his call to arms. But many scientists and wildlife experts decry the friendly-looking character and the policies he represents, saying fire suppression can be harmful to ecosystems.

A study published earlier this month in the journal Tree Physiology adds its voice to the dissent, with its authors finding 70 years of fire absence has fundamentally changed the forests of the eastern U.S.

“Our forests are in a state of flux from these two very contrasting land-use history events,” said Marc Abrams, professor of forest ecology and physiology at Pennsylvania State University, and co-author of the study. “We had a lot of fire on the landscape during the time of Native American occupation and also during early European settlement and the associated clear-cut era — so we went from a moderate to large amount of fire to an era of overprotection. With Smokey Bear, we have lost fire, and we need to get it back. This issue is on the radar screen of foresters.”

Specifically, Abrams and co-author Gregory Nowacki of the USDA Forest Service found that tree species more sensitive to drought and fire like maple and birch have replaced species that are less sensitive, such as oak and hickory. This, they say, may have serious implications as climates shift due to global warming.

Massachusetts may not have always had so many maples, according to new research. Photo by Rhett A. Butler.
Massachusetts may not have always had so many maples, according to new research. Photo by Rhett A. Butler.

“Eastern forests are changing in a way that we haven’t seen for thousands of years, and this is basically because they have gone through major changes in disturbance regimes and land-use history,” Abrams said. “The change to less drought resistance — part of a process known as mesophication — has serious implications in a warming climate, which portends more frequent and more severe droughts.”

For their study, the researchers looked at historical human impact trends and records dating back to the precolonial period, giving them a lengthy frame of reference for their analysis. They discovered that eastern U.S. forests have changed significantly in that time, with large declines in conifers like pine, hemlock, and larch in many areas. Meanwhile, maple trees – which are sensitive to fire and do well in shade – have increased substantially all over the region.

Abrams asserts that fire suppression, along with other human activities like logging, agricultural expansion, and introduction of nonnative species, has done far more to change the nature of eastern forests than could have happened from normal shifts in the climate.

“What is particularly fascinating about our study is that while forests have changed primarily as a result of altered land-use history, they are changing in a way that likely will make them more vulnerable to future climate change, including drought,” Abrams said.

 

Citation:

  • Abrams, M. D., & Nowacki, G. J. (2016). An interdisciplinary approach to better assess global change impacts and drought vulnerability on forest dynamics. Tree physiology.

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