Source: USDA Forest Service

Figure 1. Distribution of white oak (Quercus alba), the gypsy moth’s preferred host species, by basal area (m²/ha). Basal area is closely correlated with foliage cover. Dots indicate locations of national parks in the Southeast Region.

Invasive exotic insect forest pests and pathogens (IFPs) pose a serious, permanent threat to natural and cultural resources in parks administered by the National Park Service (NPS). Though the attrition of these immigrant species is undoubtedly great, the few populations that survive are, de facto, part of the affected community, and can have a profound influence at the population, community, and ecosystem levels (Mack et al. 2000). Oak (Quercus sp.), the most abundant tree genus in many forested southeastern units of the National Park System (NatureServe, R. White, ecologist, personal communication, August 2009), is under constant threat from multiple IFPs (fig. 1, above). A serious outbreak of an exotic species with a wide host range (e.g., European gypsy moth, Lymantria dispar) could affect energy and nutrient flux in the short term (Fajvan and Wood 1996; Lovett et al. 2006). A potent exotic invasive (e.g., hemlock woolly adelgid, Adelges tsugae) could, by killing dominant tree species, alter the hydrologic processes and successional dynamics of an entire ecosystem over the long term (Ellison et al. 2005; Stadler et al. 2006; Ford and Vose 2007; Nuckolls et al. 2008). Further, IFPs’ effect on forested areas is approximately 45 times greater than wildfire because the damage is incurred over a greater area, relatively synchronous, and continuous over a period of years (Dale et al. 2001). Interactions between stressors such as IFPs and global climate change could lead to compounded effects that further increase the likelihood of long-term, unpredictable alterations to forest ecosystems (Paine et al. 1998; Hansen et al. 2001; Walther et al. 2002). Finally, their estimated annual aggregate economic damage is estimated in the billions of dollars (Pimentel et al. 2000; Dale et al. 2001). The environmental and economic damage caused by IFPs justifies their monitoring by numerous federal and state agencies, universities, and nongovernmental organizations.