Potential alpine habitat in the western USA based on treeline elevation

Purpose: create a map of potential alpine habitat in the western USA as a basis for future studies in ecology and biogeography. Location: all mountains in the continental USA west of 104° longitude. Procedure: manually identify treeline elevations; interpolate a surface of these elevations; intersect the surface with a 90-m resolution DEM; record all areas above these elevations as projected alpine habitat; for display, map the area recorded as alpine at 90-m resolution. Products: a map for display; a dataset of elevations of treeline at 268 points on 66 mountain ranges in the western USA (61) and Canada (5); a dataset of points recorded as above treeline at 90-m resolution.