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June 8, 2011

National grant awarded to determine earthwork stability at Poverty Point

The National Center for Preservation Technology and Training awarded a grant to the University of Louisiana at Monroe to investigate earthwork stability at Poverty Point State Historic Site.

Principal Investigator Diana Greenlee said the $22,000 in funding, which runs from May 2011 through June 2012, will help document the site’s history of erosion over the past 60-80 years and the effects of transitioning from woody to grassy ground cover on the site’s 3,500-year-old earthen mounds.

Greenlee is an adjunct assistant professor at ULM and station archaeologist at the site.

Located near Epps, Poverty Point is well known for its elaborate earthen architecture, most of which dates to the major period of occupation and construction from about 1700-1100 B.C.

“For years, the earthen mounds at Poverty Point State Historic Site have been covered with trees, mostly oak, hickory, and sweetgum,” said Greenlee. “The trees were becoming, as they aged, increasingly susceptible to falling during windstorms and other weather events.”

Greenlee explained that when a tree falls, the roots often bring a lot of soil with them, disturbing the archaeological deposits beneath them and creating an opportunity for erosion. By blocking sunlight, the trees also prevent grass from growing; leaving bare patches of earth that could erode.

“A grassy ground cover would seem to be a more stable surface compared to the trees,” Greenlee said. “But there are no quantitative data available on managing earthen landscapes. Also, transitioning between one ground cover and the other creates potential hazards for the earthworks.”

The Louisiana Office of State Parks recently embarked on a project to remove the trees from the four oldest mounds at the site and establish a grassy ground cover, presenting a unique opportunity to use tree-ring dating of surface processes to estimate the rate of soil loss, according to Greenlee.

“Relevant methods include looking at the anatomy of the wood to identify both the location of the ground surface when the tree sprouted and when lateral roots were exposed to air,” she said.

“We can also establish control points that allow us to monitor soil loss during the transition to a grass cover. In addition, records of earthwork disturbance by wind-thrown trees over the past decade will allow us to model what kinds of damage to the mounds might have occurred in the future had the trees not been removed.”

Greenlee said the research will provide a set of methods for other earthen landscape managers to assess the processes affecting their earthworks and also make available baseline data about the impact of transitioning from a woody to a grassy ground cover, information that would have been very useful when the Louisiana Office of State Parks began this major project.

She will collaborate with Dr. David Stahle, distinguished professor in the University of Arkansas Department of Geosciences, for the project. Stahle is also founder and Director of UA’s Tree-Ring Laboratory. 

ULM Associate Professor Sean Chenoweth of the Department of Atmospheric Science, Earth Science and Physics will assist with GIS and computer modeling, and Andrea Shea Bishop, a biologist with the Tennessee Department of Environment and Conservation, will assist with tree identification. 

The complex includes four earthen mounds, with a fifth one added some 2,500 years later, and six concentric, semi-elliptical earthen ridges and a 35-acre plaza. 

Poverty Point was at the center of a vast raw material acquisition network that covered a large swath of the eastern United States, with stone and ore coming from Iowa, the Great Lakes region, Ohio, Tennessee, Georgia, Missouri and Arkansas.

It is the largest, most complex archaeological site of its age in North America, and it has the second largest constructed earthen mound.

The Poverty Point Station Archaeology Program is a collaborative effort between ULM and the Louisiana Department of Culture, Recreation and Tourism. Poverty Point is on the U.S. World Heritage Tentative List, with the eventual goal of inscription on UNESCO's World Heritage List.

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