Gypsy Moth In North America

The purpose of this research was to study how two silvicultural treatments that reduce stand susceptibility or vulnerability prior to potential gypsy moth defoliation, affect gypsy moth dynamics, defoliation, and tree mortality. The objective of presalvage thinning is to reduce stand vulnerability through reduction in stand density by removing high hazard trees (i.e., those trees which have the highest probability of dying following defoliation). The trees in the thinned stands can then increase in vigor and be even more likeley to survive defoliation. The objective of sanitation thinning is to reduce stand susceptibility, the likelihood of defoliation, through reducing the highly susceptible species (mostly oaks) component of the stand and keeping the resistant and immune components. In this study, sixteen stands (four pairs of each treatment), ranging from 19.3 to 31.2 acres and accounting for a total of 408 acres were selected in 1989. A pair represents two adjacent stands of similar species composition and size structure, and reflects comparable suitability as host for the gypsy moth. One of each pair was thinned in Fall, 1989 or early Spring 1990. Defoliation followed in six stands in 1990 and in 1991. Each of the six stands incurred over 50% defoliation of preferred species and over 40% defoliation of all species for two years. Defoliation on the other stands, i.e. background defoliation level, was less than 15% of all species, including preferred.

The gypsy moth is known to feed on several hundred different tree species. Among these species there is considerable variation in preference and performance. A listing of all tree species and their relative suitibility for gypsy moth (grouped into 3 catagories) can be found in USDA For. Serv. Gen. Tech. Rep. NE 211. On the West Virginia University forest, where this study was conducted, most of the preferred tree species were oaks.

An account of what the site may have looked like at the time of first European settlement.

"The following day we crossed Chestnut Ridge, the last of the mountain ranges. This chain is so named from the immense forests of chestnut trees that clothe its sides and summit, for nearly the whole of its extent in Pennsylvania and part of Virginia. The soil is sandy and rocky; and so exactly adapted to the growth of this tree, that no part of the world produces it more abundantly. In fruitful years the hogs from a distance of twenty or thirty miles were driven by the inhabitants to fatten on its fruit. Bears, wild turkies (sic), elk and deer traveled from afar to this nut producing region, and luxuriated on its bountiful crop."

Hildreth, S.P. 1843. Early emigration or the journal of some emigrant families across the mountains from New England to Muskingum in 1788. American Pioneer 2:112-134

Since the late 18th century the area has been heavily disturbed. Charcoal manufacture for the iron industry accounted for early use of the timber resource, followed by specialty wood products such as railroad ties and whiskey barrels. Nearly all of the Forest was eventually clearcut and much of it burned by the early 1930's.

Here is a table showing some statistics about each of the 16 stands before and after thinning.

Very heavy defoliation occurred in stands 7, 8, 13, 14, 15 & 16 in 1990 and 1991. These effects can be seen in the change in basal area in Stands 13 (thinned) and 14 (unthinned).

Some photographs from the WVU forest sites

Changes in egg mass densities at the WVU forest sites

This information was prepared by R. Muzika, A. Liebhold , and E. Luzader, USDA Forest Service, Northeastern Forest Experiment Station, Morgantown, WV 26505.

If you have any questions about this study, direct your questions to Kurt Gottschalk, project leader, RWU 4557, "Silvicultural Options for the Gypsy Moth" USDA Forest Service, Northeastern Forest Experiment Station, Morgantown, WV 26505.

Links back to related USDA Forest Service information

• Forestry Sciences Laboratory, Morgantown, WV
• RWU 4557 Silvicultural Options for the Gypsy Moth
• Northeastern Forest Experiment Station
• Gypsy Moth in North America

USDA Forest Service - Northeastern Research Station
Last Modified: Friday, 22 August 2003 at 17:48:24 EDT