Impacts of oak decline, gypsy moth, and native spring defoliators on the oak resource in VirginiaThis article is part of a larger document. View the larger document here.
The oak-hickory and oak-pine forest types dominate much of the southern landscape. In the Blue-Ridge and Appalachian Mountains of western Virginia, oak as a percentage of total forest volume can be as high as 60 percent. Much of this forest type is represented by older aged cohorts with little potential for oak regeneration to replace declining codominants. Oak decline is a prevalent natural phenomenon across the landscape, brought about by aging cohorts growing on poor sites, and exacerbated by inciting factors such as recurring drought and insect defoliation events. In Virginia, the gypsy moth (Lymantria dispar L.) has been the primary spring defoliator of oaks since the mid-1980s, although outbreak populations have been moderated since the mid-1990s by the gypsy moth fungus, Entomophaga maimaiga. In addition, several native defoliators have produced periodic outbreaks since the 1950s, particularly the fall cankerworm. The fall cankerworm (Alsophila pometaria) is the most common native defoliator of Virginia’s oaks, producing outbreaks somewhere in the State about every 5 years for the last 65 years or so. According to detailed historical records, these outbreaks seem to be getting worse in terms of acres impacted by defoliation. Other native defoliators have also had periodic outbreaks over this time period, albeit less frequently than the fall cankerworm. These include the forest tent caterpillar (Malacasoma disstria), variable oakleaf caterpillar (Lochmaeus manteo), linden looper (Erannis tiliaria), oak leaf tier (Croesia semipurpurana), and half-winged geometer (Phigalia titea). Collectively, these insects produce recurring stresses on the oak resource that, in concert with periodic drought stress, could significantly exacerbate ongoing decline and punctuate mortality events.