1U.S. Army, Corps of Engineers, Cold Regions Research and Engineering Laboratory, 72 Lyme Rd., Hanover, NH 03755, U.S.A.
2Department of Biology, San Diego State University, San Diego, CA 92182-0057, U.S.A.
3Forest Soils Laboratory, The University of Alaska, Fairbanks, AK 99775-0760, U.S.A.