1. Pacific Northwest Research Station, USDA Forest Service, Seattle, WA 98195, USA
2. Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR 97331, USA
3. Geophysical Institute, University of Alaska Fairbanks, PO Box 757320, Fairbanks, AK 99775, USA
4. Pacific Northwest Research Station, USDA Forest Service, Anchorage, AK 99503, USA