Changes in a hemlock-dominated forest following woolly adelgid infestation in southern New England¹

A foundation tree at the precipice:Tsuga canadensishealth after the arrival ofAdelges tsugaein central New England

“…All of these are poised to be successful replacement species for hemlock in our study area. Birch and the other hardwood species have already begun to replace hemlock in southern New England and the mid-Atlantic region , Small et al 2005, Eschtruth et al 2006 and are predicted to replace hemlock across much of the eastern U.S. (Kincaid 2007, Albani et al 2010, Spaulding and Rieske 2010. In terms of understory vegetation, many of the forests we examined had low species richness and abundance, conditions that are common in healthy hemlock forests (Rogers 1980, D'Amato et al 2009.…”

Response of Bird Populations To Long-Term Changes In Local Vegetation and Regional Forest Cover

“…Although hemlock was previously the most dominant species in the forest canopy in terms of stem density, basal area, and frequency, there were few surviving hemlocks in the study area by 2002 (Small et al 2005). Not surprisingly, the hemlock associates showed the strongest relationship with the second vegetation principal component, rising in abundance as eastern hemlock became increasingly dominant in the forest canopy prior to the adelgid's arrival.…”

“…This group includes flycatchers, which often perch on exposed snags while looking for food, and species such as Hooded Warbler and Veery that benefit from dense shrubs that develop in stands of dead trees Yamasaki 2001, Becker et al 2008). Although the hemlock woolly adelgid arrived in the Connecticut College Arboretum in 1987, mortality did not begin to increase until after 1992, and subsequent changes in forest structure took even longer, which may explain the delayed response of this group of species (Small et al 2005). Perhaps more importantly, the abundance of these species in the study area is determined by the characteristics of the understory, including areas where hardwoods were always dominant.…”

“…Many shrub species that are frequent in the study area show a significant positive relationship to this ordination axis indicating that they have declined. In contrast, invasive, introduced shrub and vine species such as Berberis thunbergii, Celastrus orbiculatus, and Lonicera japonica increased in the years since the hemlock decline (Small et al 2005), but they still occurred in only 3.1% of the vegetation plots in 2012 (CCJ, unpubl. data).…”

“…In 1962, the study area was categorized as a primarily oak-hemlock forest (Niering and Goodwin 1962), but the site has undergone a severe decline in eastern hemlock (Tsuga canadensis) since the arrival of the hemlock woolly adelgid (Adelges tsugae) in 1987 (Small et al 2005). The only non-forested areas within the study site are small areas of open water and low herbaceous and shrub vegetation in two small bogs (0.5 and 0.8 ha; Niering and Goodwin 1962).…”