Treesearch

Loss of populations and individuals within species to human-induced selective forces can result in loss of specific genes and overall genetic diversity upon which productivity, ecosystem stability, long-term survival, and evolution depend. This is particularly true for long-lived organisms, such as forest trees, because genetic diversity confers adaptability necessary for trees to persist across temporally and spatially variable environments. Forest management is an anthropogenic force by which forest managers selectively remove individual trees from a population leaving a residual stand...

In order to quantify relationships between environmental factors and the distribution of eastern hemlock (Tsuga canadensis (L.) Carr.) and other tree species, sites were established every 100 m along four contour lines, lying at 455 m (1500'), 610 m (2000'), 760 m (2500') and 915 m (3000') on Mt. Ascutney, a monadnock in the Connecticut River valley of eastern Vermont that rises to 960 m (3150'). At each site, basal areas of all trees were determined with a 2.5 BAF metric prism. Dominance, or relative basal area per hectare, of each species was then calculated. At each site, slope, aspect...

Eastern hemlock (Tsuga canadensis (L.) Carr) is the dominant species in a variety of sites in Great Smoky Mountains National Park. Hemlock covers approximately 3820 acres (1528 hectares) or one percent of the Park, which at 524,856 acres is the largest area managed as wilderness in the eastern United States. Since timber was never harvested in about 20% of the Park, many of the hemlock areas are virgin forests containing trees exceeding 400 years of age. From 1992-1995, Park resource managers began to identify, map, and gather baseline information on hemlock forests. Approaching infestation...

The hemlock woolly adelgid, Adelges tsugae Annand, is generally believed to be native to Asia and is known to occur in India, Japan, and China. In China, there are approximately four species of hemlock that grow in 14 provinces. We explored regions of the Southwestern Plateau in Yunnan, Sichuan, and Shaanxi Provinces for the adelgid and its natural enemies. The montane- forests of this region are largely in their natural state and noted for their biological diversity. We found the hemlock woolly adelgid in all three provinces and on each hemlock species examined (Tsuga dumosa (D. Don)...

The rate of decline of hemlock (Tsuga canadensis) trees infested with hemlock woolly adelgid (Adelges tsugae) appears to be highly variable and site dependent. Rates of hemlock forest decline have not been quantified at the landscape scale and reasons for observed variations in the rate of decline remain unknown. Others have suggested that site characteristics and/or landscape features, hemlock woolly adelgid (HWA) dispersal patterns, weather and climate, genetic variation, and a host of other factors may play a role in structuring this apparent variation in the rate of decline. In this...

High resolution paleoecological analyses from Shepherd Lake, Ontario, Canada, show that 10 to 100 year lake level fluctuations due to climatic change were responsible for alterations in the aquatic biodiversity 5,700 to 5,100 years ago. Thermophilic aquatics such as the Bushy pondweed Najas flexilis, charophyte algae and aquatic invertebrates indicate water level fluctuations of several meters, which were likely linked to a warm, dry summer climate. Pollen analysis and radiocarbon dating at Wilcox Lake shows a hemlock decline at 5800 years ago that lasted 1,000 years. Multiple regression...

Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae) is native to Japan where it is an innocuous inhabitant of Tsuga diversifolia Masters and T. sieboldii Carriere. Native populations of this insect are regulated by host resistance and natural enemies. However, introduced populations in eastern North America attain damaging levels on T. canadensis (L.) Carriere and T. caroliniana Engelmann and are regulated mainly by weather and negative density-dependent feedback mechanisms related to host deterioration.

Although many insects and diseases are associated with hemlock, we will, ironically, draw our first conclusion, that hemlocks are very sensitive to the stress of insect defoliation, from a tale of gypsy moth defoliation. The unprecedented gypsy moth (Lymantria dispar L.) outbreak of 1981, when nearly 13 million acres were defoliated in the Northeast (Fig. 1), resulted in hemlock snags throughout the hardwood forest at West Point, New York (and many other locations), in 1986. There were so many larvae in May 1981 that all the preferred hardwood leaves were eaten and the caterpillars still...

Laricobius nigrinus (Coleoptera: Derodontidae) is being evaluated as a potential biological control agent of hemlock woolly adelgid (HWA), Adelges tsugae (Homoptera: Adelgidae) Annand in eastern North America. HWA is not considered a pest on western species of hemlock (McClure et al. 1996). A combination of natural enemies and host resistance likely play an important role in maintaining levels of HWA below economic thresholds. We are studying L. nigrinus because it may play a role in regulating HWA abundance.

The hemlock woolly adelgid (Adelges tsugae Annand.), an introduced pest specializing on eastern hemlock (Tsuga canadensis (L.) Carr.), threatens to cause widespread hemlock mortality in New England forests. In this study, we used a stem-based model of forest dynamics (SORTIE) to predict forest development in a northeastern forest both with and without eastern hemlock. In all simulations, forest development was explained by species-specific life-history characteristics such as growth, mortality, and recruitment as they relate to light availability. Forest composition after 500 years...