A Novel, GIS-Based Approach to Developing Ecological Sites in Highly Variable Landscapes of the Eastern US.

Development of Ecological Sites (ESs) with associated State-and-Transition Models (STMs) has long been a foundational component of land management plans in the vast landscapes of the western United States.  In contrast, this approach to landscape characterization and anticipation of disturbance- and management-driven ecological dynamics has been slow to take hold in the eastern United States.  This time lag may be due, in part, to the unique challenges associated with developing ESs within highly variable eastern landscapes as well as conceptualizing STMs on lands with several centuries of sequential, multifaceted land-use history.  However, the basic concept of ESs is well rooted within the ecological literature of the eastern United States.  Furthermore, development of ESs and STMs within this landscape offers new opportunities to unite academic and applied ecologists around the central theme of understanding how landscape context mediates dynamic ecological responses to disturbance.  We illustrate these points by presenting preliminary results of a study wherein we define a series of topographically based ESs in the Deep Valleys Physiographic Province of north-central Pennsylvania (DVPP).  The DVPP is largely composed of a deeply incised plateau of sedimentary rocks and is experiencing rapid development of shale-gas resources.  We take a novel, GIS-based approach to ES development, which focuses purely on the multivariate relationship among four geomorphological variables derived from a 10-m resolution digital elevation model and the bedrock type.  Geomorphic variables include (1) elevation, (2) landform index, (3) topographically defined potential soil moisture, and (4) aspect.  These variables along with bedrock geology displayed a strong correlation structure.  An iterative approach was used to objectively determine the optimal number clusters to be used in a k-means cluster analysis, which ultimately delineated X ESs.  We leveraged the historical record of early settlement in the eastern United States by quantitatively defining reference states for each ES via GIS analysis of geo-referenced warrantee maps, depicting location and species information for a total of 1602 witness trees on tracts of land surveyed between about 1790 and 1810.  Current community phases were assessed via analysis of modern plot data and stand tying performed by the Pennsylvania Bureau of Forestry.  Though preliminary, these analyses allowed us to define ecological sites on public lands under shale-gas development pressure, which provides a first step toward developing management-ready STMs in this complex landscape.