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Researcher looks at the enduring impact of land use on an ecosystem

Wednesday, October 30, 2013

LAWRENCE  — Land use by past generations of humans imprints a legacy on the landscape, even decades after an ecosystem may appear to have recovered.

Now, Sharon Billings, associate professor of ecology and evolutionary biology at the University of Kansas, has earned a five-year, $545,520 grant from the National Science Foundation to participate in the establishment of a “Critical Zone Observatory” in Union, S.C., to study how an ecosystem that once was transformed for agricultural production continues to be influenced by that usage long after the activity has ceased. The work will take place at the Calhoun Experimental Forest.

“Much of the land in southeastern North America was covered in hardwood forests when Europeans first arrived, and subsequently transformed into cotton plantations,” said Billings, who holds a joint appointment as an associate scientist at the Kansas Biological Survey. “By the early 20th century, much of the land was severely degraded by erosion. In the 1950s, the U.S. Forest Service established a loblolly pine plantation on what is now a key part of the Calhoun plots. Those trees have developed into a closed canopy forest, and some plots have now been harvested and re-planted into pine. The soils in this region are naturally easily erodible, and steep gullies resulting from agriculturally induced erosion are a clearly evident sign of past land use, though many of them are now forested.”

The new observatory in South Carolina will be developed by a team of investigators from multiple universities and led by Duke University’s Daniel Richter, a champion of long-term soil experiments such as those already conducted at the Calhoun. The Calhoun CZO will be one in a larger network established by the NSF to coordinate study of the interaction of water, ecosystems and the atmosphere between the top of the bedrock underground to the treetops aboveground. 

“All Critical Zone Observatories focus on integrating processes from the bedrock to the atmospheric boundary layer, so there is quite a bit of focus on geologic substrate and how it has influenced the soil types found at the site, and in turn how those soils govern ecosystem functioning,” Billings said.

Billings’ research centers on flows of carbon, nitrogen and water in terrestrial ecosystems. She will lead KU’s contribution to the project, focusing on how a forested ecosystem recovers from human-induced disturbance, and putting it into a context of continual ecological change over the past two centuries.

“The Calhoun Critical Zone Observatory has a unique role to play in the CZO network by helping us to integrate past human activities into these processes,” she said. “The hypotheses we will be testing are focused on how human intervention in this system since European arrival has altered the functioning of the region, and perhaps has shifted the system to a new way of functioning from which it is difficult to deviate. We will explore whether the apparently recovered forests mask key changes in ecosystem functioning since before row crop agriculture, using reference hardwood stands as a guide.”

Much of the work surrounding the network of Critical Zone Observatories relates to climate change. Although the new CZO observatory will be concerned primarily with the aftereffects of land-use, the work will have a direct bearing on the study of climate.

“The Critical Zone is important for understanding effects of climate change and land-use change because it is here that the Earth system both is influenced by climate and feeds back to it,” said Billings. “Assessing how multiple Critical Zones across the CZO network function in different climate regimes can help us to predict how ecosystems will function in the future.

“More broadly, the work will help us understand fundamental controls in soils on soil organic carbon transformations, applicable anywhere. The history of Kansas since Europeans first arrived and introduced row crop agriculture is very relevant here, though it is many miles away from the Calhoun CZO. The story our work at the Calhoun CZO will tell is one of land use change, ecosystem degradation, and ecosystem recovery – a story that is being written all over the globe, particularly in places supporting row crop agriculture where erosion rates can be high. We hope to develop a greater understanding of cycles of degradation and recovery relevant to many of these places.”

Billings said that the impact of changes to both land and climate would have growing importance for humanity, adding a sense of urgency to her research.

“The most concerning feature of my work is the idea of positive feedbacks — that is, that with a change imposed by humans, whether it be climate or land use, we inadvertently change ecosystem function in a way that, in turn, influences climate in unanticipated ways,” she said. “The response time of the Earth system as a whole can be much longer than a human lifetime, making it difficult for us to appreciate the magnitude of some of its responses to current scenarios.”

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