Climate change did not play a significant role in changes seen in the composition of forests in the eastern United States, according to a new study. Effects from the warming period experienced worldwide over the last five centuries has largely been overwhelmed by local effects, researchers concluded.

Forests in the eastern United States have undergone significant changes since the 1930's, when fire prevention programs first became common.

"Over the last 50 years, most environmental science has focused on the impact of climate change. In some systems, however, climate change impacts have not been as profound as in others. This includes the forest composition of the eastern U.S.," Marc Abrams, professor of forest ecology and physiology at Penn State University, said.

Gregory Nowacki from the U.S. Department of Agriculture (USDA) Forest Service worked with Abrams and compared modern woodlands with evidence left from ancient trees. The researchers were hoping to find how forests responded to changes in temperatures and precipitation, including other environmental stresses, such as forest fires.

Forest fires, bark beetles and wind are driving forces in shaping forests, effects which are becoming more pronounced over the last few decades.

The Euro-American period, which began 500 years ago and extends to the current day, shows records of forests responding in a manner consistent with a warming period. Many of the pre-settlement forest maps used in the study were created by the earliest European explorers to the New World.

"To the north, intensive and expansive early European disturbance resulted in the ubiquitous loss of conifers and large increases of Acer (maple), Populus (poplar) and Quercus (oak) in northern hardwoods, whereas to the south, these disturbances perpetuated the dominance of oak in central hardwoods," Abrams said.

Mesophication is a name given to the process of forests growing thicker and denser, allowing less light to reach the ground. The effect can occur when a wooded area has not experienced a fire in a long time. In extreme cases, this can lead to problems with the life cycle of the forest. Forest fire prevention efforts increased the number of areas where mesophication is occurring, beginning in the mid-20th Century, according to the report.

Trees are long-lived, and their environment is often heavily affected by environmental changes brought about by outside forces, making them an invaluable resource for studying the climatic record.

Study of the role of climate change on forests in the eastern United States was published in the journal Global Change Biology

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