Nov. 3, 2000 ATHENS, Ohio - Studies of a 373-year-old white oak found in an Ohio old-growth forest suggest it is the oldest recorded hardwood east of the Mississippi. But while this ranking is exciting to the researchers studying the forest, they are more interested in what the tree can tell them about the climate and ecology in the region over nearly four centuries.
The region's oldest oak, felled during a 1998 storm, is one of 10 under scrutiny by environmental and plant biologists at Ohio University who do research in Dysart Woods, a university land laboratory in Belmont County in southeastern Ohio. Scientists use this information to track how climate and drought conditions affect tree growth. The undisturbed old-growth forest provides a clear picture of what a forest would look like without human intervention.
"Any one of us has maybe a 10- or 20- or 30-year frame of reference, but that may represent less than 10 percent of a life span of a tree," said Brian McCarthy, an associate professor of environmental and plant biology in the College of Arts and Sciences. "Studying the tree allows us to reconstruct fairly clearly what's been happening over the past 400 years."
Such information is useful for determining weather patterns for years without recorded climate data. Studying old trees gives researchers insight into climate and ecological patterns of this region and, perhaps, a glimpse of future climatological patterns for Ohio. Studying the tree rings also indicates how adverse weather conditions affect a tree's life.
Scientists date trees by counting the number of rings inside a tree's trunk. They determine climatological and ecological data by examining the size and structure of the rings. The researchers' studies revealed that droughts cause a decrease in growth, characterized by a thin ring of xylem, which is the tissue of a tree.
When water resources are scarce, a tree diverts available water to the leaves so it can maintain a healthy crown. During a severe drought, the tree doesn't take in enough water to maintain normal wood growth. McCarthy's study, published in a recent issue of Journal of the Torrey Botanical Society, found that this limited growth can continue for five years after a drought.
The studies also have allowed the researchers to fill in gaps in the climate history of the region, which only has been accurately recorded since 1950. Researchers identified which years reported droughts during the last 50 years and found the corresponding rings in the tree samples. They used these as a guide to identify other rings associated with drought years throughout history.
"That allows you to then infer backward and then we can determine, for example, that there were droughts in the 1600s, which might have had a big influence on Native Americans or the early settlers in the late 1700s," McCarthy said.
Because climate data for the past 400 years is limited nationwide, McCarthy said researchers use information from studies of old oaks, such as this project, to track global warming trends for the east. Bristlecone pine trees in the west are used to determine climate patterns for thousands of years and serve as the primary data to illustrate global warming.
The study also suggests that human misuse of the environment might affect the health of trees. During a period that lasted from the early 1800s to about 1950, there was a continual increase in the size of the rings, suggesting healthy tree growth. But after 1950, the growth rate began to decline, possibly due to human impact on the environment, McCarthy said.
While the discovery of a 373-year-old oak tree is important, McCarthy said he believes there are many trees in Dysart Woods that may be even older. Studies of this old-growth forest are continuing, work that McCarthy said could lead to an even clearer picture of past and future climate conditions.
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