A recent Dartmouth-led study on climate change broke away from traditional critical dialogue to discuss the potentially positive impact of warmer global temperatures on some forests. The article, published in the journal Ecological Monographs, is the most comprehensive review yet of how climate change impacts forests, compiling data from 500 scientific papers in fields including insect physiology, tree physiology and natural resource economics.
Biology professor Matthew Ayres and ecology and evolutionary biology postdoctoral research assistant Aaron Weed led the study in collaboration with a colleague from the University of Idaho. The article contributed to the National Climate Assessment, a government project that compiles climate change studies from various institutions around the country.
The National Climate Assessment tracks a variety of issues related to climate change, including levels of invasive plants, windfall, drought and more. Ayres and Weed focused primarily on the effects of warmer winter temperatures on the population dynamics of native forest pests, such as the southern pine beetle.
Ayres previously worked on the National Climate Assessment of 2000, in which he predicted that rising winter temperatures would move the southern pine beetle's distribution northward. The data that he and Weed gathered for the 2013 assessment supports his hypothesis, showing that the beetle has moved northward into the New Jersey pinelands due to an average seven degree increase in this year's coldest winter nights from to last year. The cold would periodically kill insects before an infestation could become entrenched.
"The cost of not managing and not being fairly aggressive in trying to control [the beetles] could change the forest type in New Jersey," Ayres said. "It's conceivable that in a decade or so, people could be driving through there and asking why it's called the pinelands because there will be no pine trees."
While the forests of New Jersey are negatively impacted by the southern pine beetle's arrival, Louisiana forests are benefiting from warmer temperatures. Weed and Ayres hypothesized that temperatures in the Deep South may have become too warm for the beetle, driving the population northward. Since the insects must be studied in their natural habitats, however, it is almost impossible to isolate which variable is causing the shift.
Louisiana forest ranger Don Smith said he noticed the change during his 20 years on the job.
"It's been relatively quiet for southern pine beetle in this part of the country," Smith said. He noted that the state had problems with the beetles in the 1980s and again in the mid-1990s but that they now seem to stay west of the Mississippi River.
Forests and People magazine editor Janet Tompkins said she has not noticed any southern pine beetle problems since moving to the state in 1994 but that she is "always on the watch."
The study showed that warmer temperatures and increased carbon dioxide in the atmosphere may cause expansion of forests, particularly in the southeastern United States. While increased forest growth in one region does not ecologically compensate for losses in another, the expansion might have positive effects on local economies, particularly timber-based ones. Weed said he did not know the exact amount of potential improvement.
"It's hard to put a dollar sign on an ecosystem service," Weed said.
Ayres said a growing role exists for the scientific process in forestry, a field previously dominated by conventional wisdom and personal experience. He added that initiatives like the National Climate Assessment will make forestry more precise and help foresters come up with tailored solutions.
"We don't have time to spend another century learning what works and what doesn't by trial and error," Ayres said.
Weed hopes others will conduct studies that take into account both the positive and negative effects of climate change on society.
"It seems like we need to be thinking about the opportunities that might exist," he said.
