1. Akita Prefectural University; Nakano, Shimo-Shinjo Akita 010-0195 Japan
2. Dep. of Land, Air and Water Resources; Univ. of California; Davis CA 95616
3. Landcare Research; PB 11052 Palmerston North New Zealand
4. Institute for Environmental Sciences, Univ. of Shizuoka; Shizuoka 422-8526 Japan