1. Institute of Forest Genetics, Pacific Southwest Research Station, U.S. Department of Agriculture Forest Service, Davis, California 95616
2. Dipartimento di Scienze Ambientali, Universita' di Parma, 43100 Parma, Italy
3. Department of Environmental Horticulture, University of California, Davis, California 95616
4. Institute of Forest Genetics, Pacific Southwest Research Station, U.S. Department of Agriculture Forest Service, Placerville, California 95667