4Weiser C J.Cold resistance and injury in woody plants [J]. Science, 1970, 169 : 1269 - 1278.
5Cannell M G R, Murray M B,Sheppard L J. Frost hardiness of red alder( Alnus rubra ) provenances in Britain [ J ]. Forestry, 1987,60:57 - 67.
6Turner J, Mitchell S J. The effect of short day treatments on containerised Douglas-fir morphology, physiology and phenology[J]. New Forests,2003,26:279 - 295.
7Li B, Howe G T, Wu R. Developmental factors responsible for heterosis in aspen hybrids( Populus tremuloides × P. tremula ) [J]. Tree Physiology, 1998,18 : 37 - 43.
8Yu Q, Tigerstedt P M A, Haapanen M. Growth and phenology of hybrid aspen clones( Populus tremula L. ×Populus tremuloides Michx. ) [J]. Silva Fennica ,2001,35 : 15 - 25.
9Hawkins B J, Henry G, Whittington J. Frost hardiness of Thuja plicata and Pseudotsuga menziesli seedlings when nutrient supply varies with season [J]. Canadian Journal of Forest Research, 1996,26 : 1509 - 1513.
10Bigras F J, D' Aoust A L. Hardening and dehardening of shoots and roots of container black spruce and white spruce seedlings under short and long days [ J] . Canadian Journal of Forest Research, 1992.22 : 388 - 396.
