Composition and Tree-Size Distributions of the Snyder-Middleswarth Old-Growth Forest, Snyder County, Pennsylvania

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 steep ravine of Swift Run in central Pennsylvania. Eighty nested quadrats sampled along 5 topographic transects (16 quadrats each) encountered eastern hemlock (Tsuga canadensis), yellow birch (Betula alleghaniensis), black birch (Betula lenta), chestnut oak (Quercus montana), red maple (Acer rubrum), striped maple (A. pensylvanicum), and eastern white pine (Pinus strobus). The occurrences of these species differed by topography. Increasing soil phosphorus and potassium, and elevation correlated significantly with shift from hemlock and yellow birch-dominated bottomlands to ridge tops dominated by chestnut oak and red maple. Increasing soil acidity was significantly correlated with the shift from yellow birch dominated quadrats to those primarily occupied by hemlock. Size distributions suggest that hemlock and yellow birch populations are stable, while those of black birch indicate episodic recruitment that may follow tree falls and other perturbations. Size distributions for chestnut oak imply impacts from white-tail deer browsing.