Relationships Between Growth Form and Stand Density in Immature Douglas-fir

Abstract

Stem form of the whole tree and branching characteristics at whorls 6 to 10 were examined in 27-year-old Dougias-tir (Pseudoisuga menziesii [Mirb.] Franco) trees established at each of three spacings (1.8 × 1.8 m, 3.6 × 3.6 m, and 4.6 × 4.6 m) and replicated across two blocks. A total of 30 trees from each spacing were analysed. Spacings were found to affect stem, crown, and branching characteristics. Tree height, diameter at breast height, and stem diameter at the base of the live crown all increased significantly with spacing (p < 0.01), while age and height at the base of the live crown both decreased (p < 0.01). Increased spacing resulted in significantly greater branch diameters at whorls 6 to 10; and, in some whorls, an increase in branch number. Swelling of the stern at branch whorls, the number of lammas whorls, knottiness ratio, and a subjective index of stem form (higher index indicates poorer form) all increased with increased spacing (p < 0.01).The considerations involved with choosing high or low initial stocking levels are discussed and the study concludes that intensive management practices such as thinning and pruning will be necessary in all regimes if clear wood is to be produced over short rotations.