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Gypsy Moth In North America


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Evaluation of Forest Susceptibility to the Gypsy Moth across the Coterminous United States

Andrew Liebhold, Kurt Gottschalk, Doug Mason
USDA Forest Service
Northeastern Forest Experiment Station
180 Canfield St.
Morgantown, WV 26505

Since the gypsy moth was originally introduced near Boston in 1868 or 1869, it has been slowly expanding its range to include the entire northeastern US and portions of Virginia, North Carolina, Ohio, and Michigan. It is inevitable that the gypsy moth will continue to spread to the south and east over the next century.

Considerable effort has been expended on documenting the spatial extent of gypsy moth defoliation via aerial sketch mapping and other techniques. This information has been used to map the spatial distribution of forests susceptible to the gypsy moth within the generally infested region (Liebhold and Elkinton 1989, Liebhold et al. 1994). In order to plan for the management of the gypsy moth over the next decade and beyond, there is a need to delimit the distribution of susceptible stands in areas that are currently uninfested.

The gypsy moth is a polyphagous insect; North American populations feed on over 300 different shrub and tree species (Leonard 1981). Despite this wide breadth of host preference, there is considerable variation within northeastern North American forests in their susceptibility to defoliation; we use "susceptibility" defined as the probability or frequency of defoliation (for a description of alternative approaches, see Twery et al. [1990]).

Several studies have focused on relating various characteristics of forests to their susceptibility to defoliation by the gypsy moth. These studies have yielded susceptibility models of varying levels of complexity. Probably the most important factor affecting stand susceptibility is the proportion of basal area represented by species highly preferred by the gypsy moth (Herrick and Gansner 1986). Other variables, such as the predominance of chestnut oak, the abundance of tree structural features (e.g. bark flaps), and various site characteristics (e.g. soils), are also known to be correlated with susceptibility (Bess et al. 1947, Valentine and Houston 1979, Herrick and Gansner 1986) but often these correlations are specific for certain regions or the variables are rarely measured in most forest inventories.

Gansner et al. (1993) demonstrated how suscpeptibility models can be applied to forest inventory data in order to map forest susceptibility at the landscape-level. In this study, we applied a similar technique to map forest susceptibility over the coterminous US.




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Last modified 10-29-03 by Sandy Liebhold .

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