1. School of Forestry, University of Montana, Missoula, MT 59801, USA.
2. Scripps Institution of Oceanography, University of California, San Diego, CA 92037, USA.
3. Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyoku, Tokyo 113, Japan.
4. NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA.
5. Department of Geography, Boston University, Boston, MA 02215, USA.