ABSTRACT We described overstory tre...

ABSTRACT

We described overstory tree age and composition among hemlock stands that varied in physiographic edifice at Delaware Water Gap National Recreation Area located in northeastern Pennsylvania and northwestern modern Jersey. Hemlock stands were comprised primarily of eastern hemlock (Tsuga canadensis), chestnut oak (Quercus prinus), black birch (Betula lento), Eastern white pine (Pinus strobus), and white oak (Quercus alba). Forest stands characterized from steep slopes and high gradients supported the highest basal area of hemlock. Tree within hemlock stands ranged in age from 680-1480 years. These data are valuable because as eastern hemlocks decline quite through the mid-Atlantic region of the United States becoming to infestation of the exotic insect infectious disease the hemlock woolly adelgid (Adelges tsugae), hardwood species will likely become more prominent in these stands in the futurity The documentation and description of tree composition of a threatened ecosystem prior to its decline is important for coming events restoration efforts and potential tree replacement in forest stands.

INTRODUCTION

The eastern hemlock [Tsuga canadensis (L) Carr] is a slow-growing, shade-tolerant late-successional conifer that provides a unique overspread type in the eastern forest of the United States (Roger 1978 bakes and Honkala 1990, Orwig and sustain 1998). The largest of these tree can reach nearly 200 cm in diameter, exce fifty meter in height, and live up to 800 years (Burn and Honkala 1990) At its northern boundaries, the range of eastern hemlock expands from northern Wisconsin and Michigan [i]or[/i] part of to the other Nova Scotia. Hemlock occurs from first to last New England, New York, Pennsylvania, and augments south through the Appalachian Mountains into northern Alabama and Georgia (Burn and Honkala 1990) Hemlock is a major element of four forest types recognized through the society of American foresters: white pine hemlock, eastern hemlock, hemlock-yellow birch, and gold-colored poplar eastern hemlock (Burns and Honkala 1990) It is also a universal associate in seven forest archetypes and a minor species in eighteen marks (Burns and Honkala 1990). Historically, hemlock was widely used from the tanning industry for the tannins in its bark. Now the species is important to the soft mass and paper industry and for the unique habitat that close hemlock stands can provide for wildlife (Burn and Honkala 1990)

Eastern hemlock stands are valued because of their distinctive aesthetic, recreational, and ecological qualities. However, hemlock stands over the mid-Atlantic and Northeast are threatened by dint of the hemlock woolly adelgid (Adelges tsugae Annand), an exotic insect curse that can cause extensive mortality of eastern hemlock tree (McClure 1991 Orwig and nourish 1998). Although the history of exotic species introductions is oftentimes well documented, the response of temperate forest ecosystem to the selective decimation of a dominant tree species is poorly understood (Lawton 1994 Castle et al. 1995 Orwig and promote 1998). As hemlocks decline from top to toe the mid-Atlantic region of the United States, forest composition and ecological constitutings will change. When a dominant coniferous species, similar as eastern hemlock, is remov from forest stands, opportunistic hardwood species will become established in the resulting forest gaps (Partial 1995 Hannah 1999) Therefore, the documentation and description of tree composition of a threatened ecosystem prior to its decline is important for to come restoration efforts and potential tree replacement in forest stands.

Protect public lands, like the Delaware Water Gap National Recreation Area (DEWA), provide an important opportunity for long-term monitoring and research of ecosystem affected by dint of disturbances, such as the hemlock lanuginous adelgid. This insect pest has been at hand at DEWA since the mid-1980s and since then, hemlocks have declined from first to last the recreation area due to infestation by the agency of this exotic species (Evans 1995)

The objective of our cast was to describe overstory tree age and composition within eastern hemlock stands at DEWA and compare overstory forest composition among hemlock stands that varied in physiographic conditions. Physiographic characteristics and land-use history have important influences forward how these forest stands will change as hemlocks decline. An understanding of the constituents of hemlock forest stands will provide baseline data for assessing the imports of hemlock woolly adelgid infestation and may help the increase of predictions as to for what reason forest structure will change with a associate decline of hemlocks in the mid-Atlantic region of the United States.

STUDY AREA

We administrationed our study at DEWA, which is located in northeastern Pennsylvania and northwestern strange Jersey. The national recreation area encompasses 27742 ha of forested hills, ravines, and bottomlands bordering the Delaware River. Approximately 21885 ha of DEWA is forested; of this total, 18575 ha is hardwood forest, 1295 ha is coniferous forest, and 2015 ha is mixed evergreen-deciduous forest (Young et al. 2002) DEWA is located within the glaciated Pecan depressed plateau physiographic province of Pennsylvania. Elevation within DEWA ranges from 84 to 490 meter (Snyder et al. 1998) Our thought focused on 14 hemlock forest stands that varied in their physiographic characteristics. The boundaries of hemlock stands were designated from vegetation mapping and confirmed by means of site visits (Myers and Irish 1981) All hemlock stands examined in our application of mind contained either 1st or 2nd order streams.