NEWTOWN SQUARE, Pennsylvania, September 27, 2011 An analysis of two decades of data collected by the U.S. Forest Service's Forest Inventory and Analysis (FIA) program shows that the live volume of hemlocks in the eastern United States is increasing despite infestations of hemlock woolly adelgid that have decimated local populations.
The information comes from an e-Science Update co-authored by scientists from two U.S. Forest Service research stations, the Northern Research Station (NRS) and the Southern Research Station (SRS), and published by SRS.
"The update provides an overview of the status and extent of hemlocks in the eastern United States based on FIA inventories conducted by SRS and NRS," according to Randall Morin, a research forester with the NRS' FIA program and the primary author. "It also incorporates research by NRS scientists and the results of pest surveys conducted by the Forest Service's State and Private Forestry Program."
Two native species of hemlock eastern and Carolina grow in eastern North America. Although a minor component in most of the forests of the eastern United States, high densities of eastern hemlock are found in New England and the mountains of the Southeast and Mid-Atlantic. The Carolina hemlock, similar in appearance to the eastern hemlock, is found only on rocky mountain slopes of the Southern Appalachian region.
Researchers conducted the analysis on 20 years of data collected across 433 counties stretching from southern Maine into northern Georgia. They found an overall increase in live-tree hemlock basal area in counties infested with hemlock woolly adelgid as well as those without infestations.
A tiny insect introduced into the United States from East Asia, the hemlock woolly adelgid, feeds at the base of hemlock needles, defoliating and eventually killing trees. "Since the insect was first noticed in the 1950s it has expanded its range at between 4.7 and 12.7 miles a ye
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USDA Forest Service - Northern Research Station