The 9-year post-treatment effects of different levels of Sitka alder (Alnus viridis ssp.
sinuata [Regel] Á. Löve & D. Löve) retention (0, 500, 100, 20 clumps per hectare) on the development of retained alder and on the growth and foliar nutrition of young, naturally regenerated lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were evaluated in the Sub-Boreal Spruce biogeoclimatic zone in central British Columbia. Alder development was inversely related to alder retention density, with the largest height and crown width increments occurring at the lowest alder densities. Low to moderate levels of alder cover (<35%) did not significantly inhibit the diameter at breast height (dbh) or height growth of lodgepole pine. Over the 9-year response period, pine dbh and height increments in the high alder retention treatment were both reduced by 11% (9 mm and 42 cm, respectively) relative to the no alder retention treatment. However, the average height of lodgepole pine, and the average height difference between the pine and alder, exceeded freegrowing guidelines for the SBSdw3 in all of the alder retention densities 6 years following treatment. Our results indicate that brushing on submesic to mesic sites in the SBSdw3 is likely unnecessary unless Sitka alder is taller than regenerating lodgepole pine and alder percent cover is uniformly very high (>40-50%) at early stages of pine development. The presence of Sitka alder improved the foliar nitrogen (N) concentration of young lodgepole pine growing on this site. However, the facilitative effects of alder retention on pine foliar N status were partially offset by an imbalance of foliar N relative to other nutrients (especially sulphur, S). Deficiencies of S (and possibly phosphorus, P, and potassium, K) induced by high foliar N levels may partially explain the smaller dbh and height growth of lodgepole pine in the alder retention treatments at this site.
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Updated March 02, 2007