Treesearch

Significant mortality of eastern hemlock, Tsuga canadensis, associated with the hemlock woolly adelgid, Adelges tsugae, (HWA), has occurred in Connecticut forests since a recent introduction of the insect in 1985. Mortality associated with HWA has also occurred recently in the Delaware Water Gap (PA and NJ) and the Shenandoah National Park (NC).

Winter water relations have been monitored in hemlock (Tsuga canadensis (L.) Carr.) at their upper elevational limits for three winters, 1997, 1998, and 1999, on Mt. Ascutney, Vermont. Hemlock and white pine trees (Pinus strobus L.) reach their elevational limit on Mt. Ascutney at 640 m (2100?), while the summit has an elevation of 960 m (3150'). Relative water contents (RWCs), water potentials, and cuticular conductances were monitored in combination with micrometeorological weather information on both species. These data were incorporated into a winter water relations model which...

Casual observations have suggested that intermediate size and age gaps may exist in the eastern hemlock (Tsuga canadensis (L.)Carr.) populations of Algonquin Provincial Park, Ontario. This was confirmed in vegetation surveys reported here. Several hypotheses, involving mortality risks at different points in the life cycle of hemlock, are proposed to explain the age gap. The hypotheses include seed predation (a period of intense seed predation), seedling establishment (a period of environmental or climatic changes limiting seedling establishment), hare browsing (a period of high snowshoe...

We assessed the species composition and structure of three riparian forest stands of differing ages (old-growth, late-successional, mid-successional), dominated by eastern hemlock (Tsuga canadensis Carr.), in the Allegheny National Forest of northwestern Pennsylvania.

Both greenhouse and field studies have shown that it is the combined stress of drought and infestation by the hemlock woolly adelgid that causes death in eastern hemlocks. In three separate greenhouse studies it was found that the presence of adelgids alone did not cause the death of the plants over a period of 1, 2 or 5 years respectively, if they were well watered and received sufficient nutrients. Another greenhouse study found that drought hastened the death of infested hemlock seedlings. This was reflected in the rapid fall in the rate of chlorophyll fluorescence. In this study the...

Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), has two generations/year that feed and reproduce on hemlock, Tsugae spp. The spring generation, present from March to June, is called progrediens. The next generation, present from June until the following March, is called sistens (McClure 1987, Gray and Salom 1996). In June, after sistens eggs hatch, they settle at the base of needles and immediately go into an aestival diapause that lasts until October, a duration of 4 months. The occurrence of aestival diapause in HWA sistens is a barrier when trying to continuously...

Clear Lake is located in the centre of the 1300 ha Clear Lake Conservation Reserve in Haliburton County, Ontario, Canada. In 1988, the reserve was designated as a protected area representing undisturbed, old-growth ecosystems. The reserve includes several headwater lakes and their associated catchments which support old-growth hemlock stands that are estimated to be up to 400 years old.

Hemlock woolly adelgid (HWA) was first observed in Shenandoah National Park (SNP) in the mid-1980s. Since then, this exotic insect has expanded its range throughout the park. Most stands were heavily defoliated within several years of infestation. However, several hemlock stands appear to be not affected or only moderately affected to the present date. To investigate this discrepancy in hemlock stand condition, we are analyzing satellite imagery from 1984, 1988-9, 1991-2, 1994, and 1997.

Scymnus (Neopullus) sinuanodulus Yu et Yao, S. (N.) camptodromusYu et Liu, and Scymnus (Neopullus) n. sp. (in press) were collected in the People's Republic of China from hemlocks infested with the hemlock woolly adelgid, Adelges tsugae Annand. To date, 3 of the 14 provinces in China where hemlock occurs naturally have been surveyed; S. sinuanodulus was found in Yunnan, Scymnus n. sp. was found in Shaanxi, and S. camptodromus was found in Yunnan and Sichuan. The three lady beetles were imported from 1996 to 1998 to the USDA Forest Service Quarantine Laboratory in Ansonia, Connecticut, for...

Hemlock ravines in Delaware Water Gap National Recreation Area (DEWA) are highly valued because of their distinctive aesthetic, recreational and ecological qualities.