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Appalachian researcher studies relationship between carbon dioxide and western coniferous tree growth; Research is funded by a $182,000 NSF grant

treecore_t.jpgBOONE—The ponderosa pine and Douglas fir are iconic images of the Northern Rockies. Towering more than 130 feet and with circumferences that can exceed 200 inches, the trees provide researchers with a wealth of information related to fire history, climate changes and tree growth trends.

Appalachian State University’s Peter T. Soulé is researching the relationship between the growth of the ponderosa pine and Douglas fir and the rise in carbon dioxide in the Northern Rockies.

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Phil White takes a core sample from a ponderosa pine in Montana as part of a research project being conducted by Dr. Peter T. Soulé, a professor in Appalachian State University’s Department of Geography and Planning. White is a graduate student in the Department of Geography and Planning. The research focusing on the relationship between the growth of the ponderosa pine and Douglas fir and the rise in carbon dioxide in the Northern Rockies is funded by a three-year grant from the National Science Foundation. (Photo courtesy of Paul Knapp)

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A team of student and faculty researchers from Appalachian State University and UNC Greensboro spent several weeks this summer collecting core samples from some 150 Douglas fir, ponderosa pine and western larch. Pictured are Steve Shelly, front row left, with the National Forest Service, Dr. Peter T. Soulé, a professor in Appalachian’s Department of Geography and Planning, and Appalachian graduate student Phil White. On the back row from the left are Justin Maxwell, a former geography graduate student at Appalachian and now enrolled in a PhD program at UNC Greensboro, and Paul Knapp, a professor from UNCG’s Department of Geography. The team is studying the relationship between the growth of the ponderosa pine and Douglas fir and the rise in carbon dioxide in the Northern Rockies. (Photo courtesy of Paul Knapp)

His work is funded by a three-year, $182,000 grant from the National Science Foundation and is collaborative with Dr. Paul Knapp for the Department of Geography at UNC Greensboro.

Soulé is a professor in Appalachian’s Department of Geography and Planning. His research focuses on mountain climatology and vegetation change. His latest research is an outgrowth of his work over the past decade related to climate change and the growth rates of coniferous trees in the western United States.

“It’s a project that has snowballed over the years,” Soulé explained. “One project leads to another. We keep coming up with new ideas that center around a main theme of carbon dioxide enrichment stimulating tree growth.”

Soulé’s research has documented the ponderosa pines’ favorable response to a carbon dioxide rich environment. Over time, the species has become more efficient at converting CO2 and water into energy or sugars. “Carbon dioxide acts like a fertilizer,” Soulé said. “Because carbon dioxide is more readily available in the atmosphere, the tree doesn’t have to work as hard during photosynthesis and is able to use water more efficiently. That makes them grow faster and continue to grow during dry seasons,” he said.

Soulé tracks the years in which the trees had fast or slow growth by analyzing the core samples taken from trees. He then compares that information to known climate data. “We match 100 year’s worth of climate data with the growth of the tree, so we know what’s causing the tree to grow, and what the patterns of growth are,” he said.

Wide bands in the core sample might indicate a wet growing season or a change in temperature. Narrow bands can indicate a year in which tree growth was poor, possibly because of a dry climate. By comparing the rings with the recorded climate data for the region, researchers can determine factors at play in the tree’s growth rate.

This summer, Soulé and graduate students took core samples from some 150 trees – Douglas fir, ponderosa pine and western larch – at three study sites in Montana. They will spend the academic year analyzing the samples. Next summer, they will sample more than 300 trees from four study sites in Idaho.

Soulé chooses locations that are as free from human impact as possible, such as Research Natural Areas, wilderness areas and areas otherwise protected from grazing, logging or fire suppression. “Our niche has always been to try and look at the effects in undisturbed natural forest environments. In that sense, we eliminate as many of the other confounding influences as we possibly can,” Soulé said.

Expanding his research to include the Douglas fir will help Soulé better determine if increased CO2 alone is driving force behind changing growth rates of trees, and how different species respond when exposed to the same environmental stimuli.

“What we have been seeing throughout the West is pretty consistent through time,” he explained. “The radial growth over the last 50 years or so has trended upward, over and above what we would expect from climate drivers. So, is there some other factor that is that is suddenly causing these trees to grow? Our work has shown that the most likely culprit for that is CO2.”

Current climate models predict that the Northern Rockies study area will experience more frequent and severe summertime droughts, Soulé explained, and this should lead to slower growth rates for the trees.

“The potential positive impacts on growth resulting from increasing atmospheric CO2 might offset any reductions in growth due to changing climatic conditions, and this could be significant because of the commercial value of these species, their role in ecosystem dynamics, and the propensity for old growth forests to serve as major carbon sinks,” he said. “A greater understanding of issues facing future ecosystems under increased CO2 and warmer, drier conditions is critical.”

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