Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation

Abstract

Hemlock woolly adelgid (HWA; Adelges tsugae Annand) infestations have resulted in the continuing decline of eastern hemlock (Tsuga canadensis (L.) Carrière) throughout much of the eastern United States. In 1994 and 2003, we quantified the vegetation composition and structure of two hemlock ravines in the Delaware Water Gap National Recreation Area. This is the first study to use pre-adelgid disturbance data, annual monitoring of infestation severity, and annual records of hemlock health to assess forest response to HWA infestation. In 2003, 25% of monitored hemlock trees were either dead or in severe decline. Measures of hemlock decline (crown vigor, transparency, density, and dieback) were correlated with HWA infestation severity and changes in light availability over the study period. Average percent total transmitted radiation more than doubled at these sites from 5.0% in 1994 to 11.7% in 2003. The total percent cover of vascular plants increased from 3.1% in 1994 to 11.3% in 2003. Species richness increased significantly, and more species were gained (53) than lost (19) from both ravine floras over the 9-year study period. Though exotic invasive plants were absent from these ravines in 1994, our 2003 resurvey found invasive plants in 35% of the permanent vegetation plots.

Foundation Species Loss and Biodiversity of the Herbaceous Layer in New England Forests

“…During this interval, species richness and cover of bryophytes (mosses and liverworts) more than doubled, in large part because of the amount of new habitat (dead and fallen branches and boles) and higher light availability on streambanks. In the same plots, all understory ferns, herbs (except for Streptopus amplexifolius (L.) DC), shrubs, and trees increased in occurrence and abundance as hemlock declined [57]. At the same time, there was a large increase-further accelerated by increasing density of deer-in abundance of nonnative species, including Ailanthus altissima (P.Mill.)…”

Evaluating a potential area-wide IPM strategy for managing hemlock woolly adelgid in the eastern United States

“…The juxtaposition of a small, select cohort of trees as a reliable indicator of overall forest health underrepresents the magnitude of the forest. It is therefore in the best interest of forest health professionals to develop large-scale projects that observe the longterm effects of various treatment methods on invasive insects (Eschtruth et al 2006, Eschtruth et al 2013. Studying on an area-wide scale is also appropriate when considering other aspects of forest management, as it relates to biological invasions (i.e.…”

How climatic conditions, site, and soil characteristics affect tree growth and critical loads of nitrogen for northeastern tree species

“…It occurs at elevations up to 730 m in New England, 300 to 910 m in New York and Pennsylvania, and from 610 to 1520 m in the southern Appalachians (Godman and Lancaster 1990). Eastern hemlock populations in the southern part of the range are often subject to infestation of hemlock wooly adelgid (Adelgis tsugae), which can result in tree death in 4-5 years (Lovett et al 2006), although tree decline may occur much more gradually (Eschtruth et al 2006(Eschtruth et al , 2013.…”