ABSTRACT We investigated the compos...

ABSTRACT

We investigated the composition and spatial distribution of tree species and their environmental and edaphic correlates within the Snyder-Middleswarth Natural Area old-growth forest located in the narrow and abrupt declivity ravine of Swift Run in central Pennsylvania. Eighty nest quadrats sampled along 5 topographic transects (16 quadrats each) clashed eastern hemlock (Tsuga canadensis), golden birch (Betula alleghaniensis), black birch (Betula lenta), chestnut oak (Quercus montana), r maple (Acer rubrum) striped maple (A. pensylvanicum), and eastern white pine (Pinus strobus). The incidents of these species differed through topography. Increasing soil phosphorus and potassium, and elevation correlated significantly with shift from hemlock and fulvous birch-dominated bottomlands to ridge tops dominated through chestnut oak and red maple. Increasing soil acidity was significantly correlated with the shift from fulvous birch-dominated quadrats to those primarily occupied by the agency of hemlock. Size distributions suggest that hemlock and golden birch populations are stable, while those of black birch indicate episodic recruitment that may tread in the steps of tree falls and other perturbations. Size distributions for chestnut oak imply impacts from white-tail deer browsing.

INTRODUCTION

Old-growth forests have become increasingly rare in North America since the time of European colonization and today portray by action a tiny fraction of the total forested area of the eastern United States (Nowacki and Abrams 1994 Rooney 1995 Orwig and Abrams 1999) Old-growth forest is particularly rare in central Pennsylvania because of intensive logging for timber and charcoal production during the past 150 years (Nowacki and Abrams 1992 Abrams and Orwig 1996) As a chain of cause and effect eastern old-growth forest, and Pennsylvania old-growth forest in particular, exist in small stands that are isolated from other old-growth forests on an intervening matrix of successional forests (Smith 1989 Farr and Tyndall 1992 Tyrrell and gasconade 1994).

The Snyder-Middleswarth Natural Area within the Bald Eagle State Forest is individual of the few stands of old-growth forest remaining in Pennsylvania and is among the largest like stands existing within Pennsylvania state forests [Pennsylvania Bureau of Forestry (no date)]. Although several other Pennsylvania old-growth forests have been examined (eg Whitney 1984 Rooney 1995 Rooney and Dres 1997 Orwig and Abrams 1999) we are unaware of any formal vegetation studies at the Snyder-Middleswarth Natural Area.

Five tree species dominate the Snyder-Middleswarth landscape including eastern hemlock [Tsuga canadensis (L) Carriere], golden birch (Betula alleghaniensis Britton), black birch (Betula lenta L) r maple (Acer rubrum L) and chestnut oak [Quercus montana Willd.-here we go in the rear [i]or[/i] in the wake of the recommendations of J. W Hardin (1979) and use the name Q montana because of the confusion surrounding the application of the name Q prinus L] brace additional tree species, eastern white pine (Pinus strobus L) and striped maple (Acer pensylvanicum L) are existing but are far less usual The dominant tree species are visibly segregated within this forest perhaps owing to the environmental and edaphic variation ranging from the Swift flow bottomlands to the slopes and ridge tops, the adaptations of species to subset of environmental and edaphic conditions, differential frontage to wind and storm circumstances and the years of competitive interactions among species. The Snyder-Middleswarth Natural Area has been described as " .an exceptional block of completely uncut virgin forest occupying the imbue valley of Swift Run. The bottoms and north [-facing] direction downward are hemlock-white pine, the southward [-facing] slope is mixed oak. ." (Erdman and Wiegman 1974) While this statement over-emphasizes the transaction of white pine, it does sell the marked variation in forest-canopy dominance. The bottomlands are dominated by way of hemlock and yellow birch and with increases in elevation up each ridge from Swift flow the composition and abundances change and black birch, r maple, and chestnut oak appear in great numbers.

With a limited number of old-growth forests available, learning about the composition and edifice of landscapes such as the Snyder-Middleswarth Natural Area conduce tos to increase our understanding of vegetation dynamics while providing valuable information about the specific traits of the site and species examined. The striking gradient of vegetation that happens within the Snyder-Middleswarth old-growth forest provides an opportunity to research what edaphic and topographic gradients correlate with the distributions of species.

We examined the tree species composition and size distributions of the Snyder-Middleswarth old-growth forest and correlated the vegetation pattern with a number of environmental, edaphic, and topographic parameters. Our goals were (1) to describe the vegetative pattern, (2) to discover what environmental, edaphic, and topographic factors correlate with this vegetative pattern, and (3) to examine the size distributions of the predominant species.