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Thinning Effects on Foliar Elements in Eastern Hemlock: Implications for Managing the Spread of Hemlock Woolly Adlegid

Photo of Photo of hemlock tree crown released by the thinning treatment. Mary Ann Fajvan, U.S. Department of Agriculture Forest Service.Photo of hemlock tree crown released by the thinning treatment. Mary Ann Fajvan, U.S. Department of Agriculture Forest Service.Snapshot : With the imminent entrance of hemlock woolly adlegid (HWA) into forest stands in the Allegheny National Forest in Pennsylvania, it was critical to understand whether silvicultural thinning results in increased foliage palatability for HWA. Forest Service research findings suggest that thinning may be used in hemlock stands without risking HWA attack due to increased needle nutritional value.

Principal Investigators(s) :
Fajvan, Mary Ann 
Research Location : Allegheny National Forest, Pa.
Research Station : Northern Research Station (NRS)
Year : 2016
Highlight ID : 1128

Summary

Silvicultural manipulations are being used to minimize the impacts of the invasive hemlock woolly adelgid (HWA) on eastern hemlock. Thinning is being tested as a means for reducing hemlock vulnerability to HWA because it increases resources for residual trees, and may affect crown growth and foliar chemistry. With the imminent entrance of HWA into these stands, it was critical to understand whether thinning may also result in increased foliage palatability for the HWA. Hemlock woolly adelgid densities have been correlated with foliar concentrations of calcium (Ca), potassium (K), nitrogen (N), and phosphorus (P). Forest Service scientists determined foliar element levels prior to and for 4 years after thinning in northwestern Pennsylvania stands of eastern hemlock. All element concentrations except Ca decreased over time. Thinning by itself did not affect the tested foliar nutrients. Treatment year interaction was significant and evident in the different temporal trajectories of foliar N and K; however, the differences between thinned and unthinned plots within years averaged only 0.03 percent for N and K. The scientists concluded that even though thinning changed the temporal trajectories, the nutritional shifts reflected decreased competition and increased growth and appeared to be a short-term effect of the treatment.

Forest Service Partners

External Partners

 
  • West Virginia University

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