Insect Guild Structure Associated with Eastern Hemlock in the Southern Appalachians

Abstract

An assessment of the insect guild structure associated with immature and mature eastern hemlock, Tsuga canadensis (L.) Carrière, at high and low elevations was made before the invasion by the hemlock woolly adelgid, Adelges tsugae (Annand), and elongate hemlock scale, Fiorinia externa Ferris. Guild dynamics were determined among 243 insect species associated with eastern hemlock in the southern Appalachians. Detritivore, hematophage, herbivore, fungivore, parasitoid, predator, scavenger, and transient guild assignments were made. The herbivore and transient guilds were subdivided into chewers, sapsuckers, flower feeders, pollen feeders, pollen/nectar/sap feeders, and seed feeders. A significant association was found between guilds on immature and mature hemlocks at low elevations, but no significant association was found at high elevations. There was also a strong association of phytophagous insects on immature hemlocks and scavengers on mature hemlocks. The observed transient, scavenger, and predator guilds had a significantly lower co-occurrence among species indicating segregation of the species within these guilds. The herbivore guild had a significantly higher co-occurrence among species than the simulated index indicating aggregation of species within this guild across sites. Detritivore, hematophage, and parasitoid guilds did not differ significantly from the simulated community. These results document a diverse and dynamic insect community on eastern hemlock before invasion by hemlock woolly adelgid and elongate hemlock scale.

Response of macroarthropod assemblages to the loss of hemlock (Tsuga canadensis), a foundation species

“…Overall, our data provide experimental support for earlier correlative observations (Ellison et al 2005b, Dilling et al 2007) that species richness and evenness of macroarthropods increases when hemlocks disappear. Our experimental data provide little evidence that competitive interactions structure assemblages of the ants, spiders, or beetles in these northern forests, but they do provide evidence for environmental filtering-far fewer species are present in late-successional hemlock stands than in disturbed forest stands or in early-successional hardwood stands.…”

“…We chose to study these three taxa because of their known utility as indicators of environmental change (e.g., Andersen 1997, Rohr et al 2007) and their known sensitivity to ecological parameters such as litter structure and depth (Bultman andUetz 1982, Latty et al 2006), temperature and moisture (Lessard et al 2011), and resource supply (Chen and Wise 1999), all of which are affected strongly by the presence or absence of eastern hemlock (e.g., Ellison et al 2005a, 2005b, Ford and Vose 2007. The results from this experimental study expand on previous correlative studies of differences in arthropod assemblages among hemlock and hardwood stands (Ellison et al 2005b, Dilling et al 2007) because they allow for stronger inferences regarding the relative importance of three different ecological mechanismscolonization from the regional species pool, environmental filtering, and interspecific competition-that control the reassembly of arthropod assemblages following loss of hemlock.…”

“…Eastern hemlock, which deeply shades and cools the forest floor and which sheds needles that form a slowly decomposing, thick, organic layer, provides unique habitats for some insects but is inhospitable to others (Ellison et al 2005a, Dilling et al 2007). Although our long-term experimental results generally support the conclusions of these previous correlative studiesthat arthropod diversity will change as hemlock declines-we are able to provide new evidence that the type of hemlock removal affects arthro- Notes: Values (and 95% confidence intervals in parentheses) in a column with different superscripted letters indicate significant differences among treatments (P , 0.05) based on non-overlap of 95% confidence intervals from an independent sampling algorithm with 1000 iterations.…”

Arthropod Diversity and Functional Importance in Old-Growth Forests of North America

“…Some herbivores are specialized to colonize only a particular plant species (e.g., the catalpa sphinx, Ceratomia catalpa, found only on catalpa, Catalpa spp., trees) or a few related plant species (e.g., red-humped oakworm, Symmerista canicosta, on related beech, Fagus grandifolia, chestnut, Castanea dentata, and oak, Quercus spp., trees), whereas others (such as the forest tent caterpillar, Malacosoma disstria), are adapted to feed on a wide variety of hardwood species, although local populations may be more restricted in diet breadth [23]. Hemlocks and cedars host particularly unique insect assemblages that complement the community in both eastern and western old-growth forests [7,17,24,25]. Typically, insects that feed on angiosperms cannot feed on conifers and vice versa, although some, such as the whitemarked tussock moth, Orgyia leucostigma, and fall webworm, Hyphantria cunea, are capable of doing so.…”

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

“…The forest floor beneath the eastern hemlock canopy is cool and dark [16,27], and the slowly decomposing hemlock needles give rise to a deep organic layer, which is very acidic and low in nutrients [28]. Unique faunal assemblages, including groups of birds [29], arthropods [30][31][32], and salamanders [33] live in eastern hemlock stands. Fungal diversity in eastern hemlock stands rarely have been studied, but in general is at best equal to, and generally lower than, that in deciduous forests [34][35][36].…”