1. Dep. of Forest Ecology; Swedish Univ. of Agric. Sci.; S-901 83 Umeå Sweden
2. Dep. of Physical Chemistry; Univ. of Umeå; S-901 87 Umeå Sweden
3. Pacific Forestry Centre; Natural Resources Canada; 506 West Burnside Rd. Victoria British Columbia Canada V8Z 1M5