Quantitative Delineation and Characterization of Hierarchical Biophysical Regions of Maine

Natural resource managers and researchers are often faced with the issue of how to subdivide large landscapes into smaller, homogeneous units for analytical or administrative purposes. We used data in a Geographic Infor- mation System and cluster analyses to divide Maine into broad-scale regions based on elevation, slope, two measures of species richness, and three weather variables. The locations and numbers of these biophysical regions were affected by variable selection, cell size (and sampling), and euclidean distances used to terminate clustering. We present rationales, largely based on our intended uses of these regions, for selecting the seven variables, a cell size (21.44 km2), and a euclidian cut-off (1.56). Thirteen biophysical regions, in fourteen units, were delineated and characterized; the regions were hierarchically arranged in five levels. Five of the seven variables used in the final clustering were abiotic versus biotic, suggesting that regions relate to potential as well as current ecological conditions. The euclidian distances defining individual regions can be used to quantify the biophysical distinctness of each region (and grid-cell).