Growth and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) in nursing mixtures established on nitrogen-deficient mineral soils

Rate of growth and wood properties of Sitka spruce (Picea sitchensis (Bong. ) Carr.) were investigated in triplet mixtures with lodgepole pine (Pinus c ontorta Loud.) (Alaskan provenance) and Japanese larch (Larix kaempferi (La mb.) Carr.), established on nitrogen-deficient, iron pan soils. These "nurs ing" mixtures were compared with pure stands of Sitka spruce that had been either regularly or periodically fertilized with nitrogen. Japanese larch p romoted a growth rate in Sitka spruce greater than that achieved in the lod gepole pine-nursed spruce and equivalent to the two pure spruce treatments over the duration of the experiment (current age 28 yrs). Growth of regular ly fertilized pure Sitka spruce was not significantly greater than that of periodically fertilized pure spruce. Alaskan lodgepole pine controlled bran ch size on the lower part of the spruce stems more effectively than the oth er treatments, although this may have been a function of tree size. Branch characteristics of Japanese larch-nursed spruce, however, were similar to t hose of the pure spruce treatments. Japanese larch caused an imbalance in c rown development in the spruce, although it is unclear from the present stu dy whether this will have an influence on stem and wood quality by the end of the rotation. Overall, the evidence from this study suggests that Japane se larch is an effective nurse of Sitka spruce on nitrogen-deficient iron p ans, maintaining a rate of growth similar to that of pure Sitka spruce peri odically fertilized with nitrogen and higher than that observed in spruce n ursed by Alaskan lodgepole pine.