|
Article Excerpt
ABSTRACT -- Eastern hemlock, Tsuga canadensis (L.), Carr is an
integral part of forested systems in eastern North America now threatened by invasions of exotic pests. Due to the threat of exotic pests, information on the species associated with eastern hemlocks was collected to compile a species listing. The insect fauna associated with eastern hemlock was assessed at four sites representing new and old growth trees and ten alternate sites in the Great Smoky Mountains National Park and adjacent areas in eastern Tennessee. Sites were sampled using malaise/pan traps, pitfall traps and direct collection. Species diversity was assessed using the Shannon index and species richness estimates were made using the program estimates. The rich insect fauna of eastern hemlocks yielded 2,832 specimens representing 292 species in 101 families and ten orders. Species richness and abundance were highest at Chimney Tops old growth site with 107 species and 801 specimens. Species richness estimators projected between 415 and 550 species associated with eastern hemlock. Several pests of eastern hemlock, including the hemlock woolly adelgid, Adelges tsugae (Annand), elongate hemlock scale, Fiorinia externa Ferris, hemlock scale, Abgrallaspis ithacae (Ferris), and hemlock looper, Lambdina fiscellaria (Guenee), as well as natural enemies of these pests, were collected.
**********
Eastern hemlock, Tsuga canadensis (L.), Carr is an important component of forests throughout the eastern United States and possesses both intrinsic and unique values. Eastern hemlocks are ecologically important representing an integral component of many old growth communities providing distinct microclimates for an array of wildlife. The areas dominated by eastern hemlocks are cool and shaded making them attractive to both wildlife and people. This tree is often found near streams where it reduces the water temperature making the stream favorable to native brook trout. Within forests where eastern hemlocks are threatened can be found a myriad of outdoor recreational opportunities, a rich and diverse assemblage of regional flora and fauna, scenic waterfalls and historic structures, as well as a variety of environmental and outdoor educational opportunities. Also, eastern hemlock is among the most widely grown evergreens in ornamental landscapes. Because of these scenic mountains in the Southern Appalachians, more than 14 million visitors annually contribute over five billion dollars to the local economy of eastern Tennessee.
Forest decline is an issue confronting the southern Appalachian region with significant damage caused by several invasive insect pests. Introduced species such as Adelges tsugae (Annand), hemlock woolly adelgid, and Fiorinia externa Ferris, elongate hemlock scale, represent pernicious pests with the potential to cause widespread destruction to eastern hemlocks in the eastern United States (Danoff-Burg and Bird, 2002; McClure and Fergione, 1977; Stimmel, 1980, 2000). Wallace and Hain (2002) concluded that none of the four established predators collected from eastern hemlock had a significant impact on populations of hemlock woolly adelgid. The Great Smoky Mountains National Park (GSMNP) includes some of the largest remnants of eastern hemlock in the world, which are presently confined to about 35,399 ha at various elevations. Because information on the status of the insect fauna on eastern hemlock within the region is lacking, this study was initiated to identify and assess those insect species associated with this important tree.
MATERIALS AND METHODS
Four primary test sites (each 20 m by 40 m), each consisting of three trees, were established representing mature and new growth hemlocks at high and low elevation gradients within the GSMNP in eastern Tennessee. Two lower sites (760 m) at Elkmont representing new (35[degrees]39'56.388"N, 83[degrees]35'04.915"W) and old (35[degrees]39'47.733"N, 83[degrees]35'10.036"W) growth trees and two higher sites (1,149 m) at the Chimney Tops representing new (35[degrees]38'1.74"N, 83[degrees]28'11.4"W) and old (35[degrees] 37'49.44"N, 83[degrees]28'3.18"W) growth trees were selected for study. These sites were located in areas not infested by the hemlock woolly adelgid. Each site consisted of three old growth (diameter at breast height > 20 cm) or new growth (diameter at breast height; dbh < 20 cm) trees. The Elkmont new growth site is located in a xeric oak forest (type 7) and the Elkmont old growth site is part of a pine forest (type 9). Chimney Tops old growth is located in a tulip poplar forest (type 6), while the Chimney Tops new growth site is located in cove hardwoods (type 3). Specimens were obtained from these four sites using Malaise/pan traps, pitfall traps, and direct (beat-sheet, sweep-net and handpicking) sampling from 1 June 2002 through 30 November 2002 and from 5 June 2003 through 2 September 2003.
Modified malaise/pan traps were placed in the tree canopy of each of three trees at the four primary test sites in the GSMNP to sample the insect fauna. Trap frames were constructed using PVC pipe (60 cm by 60 cm by 60 cm) and covered with polyester netting (#156). The collecting unit consisted of a plastic cup (60 mm wide by 65 mm deep, 120 mL volume) that contained 30-60 mL of 50% propylene glycol (Sierra[R]) and tap water. The pan (15 cm wide by 65 cm wide by 12 cm deep) was hung under the frame and contained 900-1000 mL of 50% propylene glycol and water. Samples were obtained from all collection units and pans biweekly, labeled, and taken to the laboratory for processing. Pitfall traps were used to sample ground-dwelling species at two trees per site. Four shallow holes (8 cm deep; one in each cardinal direction at the canopy's peripheral edge) per tree were dug into the ground for placement of traps. Each trap consisted of two plastic cups (60 mm wide by 65 mm deep/120 mL volume) with a plastic cover. One cup was placed inside the other to aid in sample collection and reduce flooding. The outer cup had a drainage hole, while the inner cup was filled with a 50% mixture of propylene glycol and tap water. Plastic covers with 90[degrees] directional fans were placed on the surface of the ground above the pitfall traps to prevent flooding and direct insects into the trap. Two pitfall traps at each tree were retrieved every 14 days/site and taken to the laboratory for processing and identification. On each sampling date, the collection cup with preservative was removed and replaced with fresh preservative. Visual observations and direct sampling of insects were conducted every 14 days (15-20 min/tree) within each study site using...
|
