Composition of Canyon-Slope Woodlands in Zoar Valley, Western New York, as Associated with Slope Orientation and Elevation

Abstract

The 11 km long and 50-140 m deep Zoar Valley Canyon in western New York State represents a nearly undisturbed riparian ecosystem. Forest composition and age structure have previously been studied on riverside floodplains and raised terraces, but the slopes above were heretofore unexplored. The present study aimed to catalogue tree species distributions on 20-60 degree slopes that also tend to be solidly forested. Two major objectives were to evaluate the influence on forest composition of north vs. south slope orientation and elevation above the river bed. Additionally, multivariate Non-metric Multidimensional Scaling (NMDS) ordination was used to assess the relative roles of different slope communities in providing colonizers to the lower elevation fluvial landforms. A clinometer and laser range finder were used to measure slope angles and elevations of safe vantage points and of individual trees. Trees were identified to species and classified as understory, midstory, canopy, and emergent. South-facing slopes >40 m above the river supported xeric canopies, often <10 m in height, dominated by Quercus rubra, Q. prinus, and Pinus resinosa (57-93% of trees collectively). In contrast, north-facing slopes supported >30 m tall mesic canopies (Acer saccharum, Fagus grandifolia, Tsuga canadensis, Fraxinus americana, Liriodendron tulipifera) across their entire vertical profiles. Eastern hemlock was notably more abundant on mesic north-facing slopes than on terraces below (27-48% vs. 2-27%, respectively), especially above 40 m where it comprised 42-58% of trees. Ordination results suggest xeric communities play little role in floodplain/terrace colonization (communities were widely separated in ordination space), but that mesic slopes have variable influence on the flats below.