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Quantifying effects of different levels of canopy tree retention on stocking and yield of the regeneration cohort in the southern interior of British Columbia
Variable retention has become a prominent silvicultural strategy for meeting multiple resource management objectives. Under this strategy, retained trees contribute to the structural complexity of the subsequent stand, and provide habitat for wildlife and shelter for regeneration and understory vegetation. Retained trees, however, affect the stocking and yield of the young tree cohort to some degree. The effects of retained trees vary by the spatial arrangement of retention (group or dispersed), attributes of retained trees (type of species, condition, size and frequency), site, and other factors.Under a variable-retention strategy, accurate growth and yield predictions for the resulting two-tiered stands are required. This paper outlines the effects of retained trees on understory tree development and compares various approaches that are used to model and simulate the effects of different levels of retention on yield at rotation. Specific simulations were conducted to quantify the effects of retained trees on seedling stocking and future yield for pure lodgepole pine (Pinus contorta Dougl. ex Loud.) and interior spruce (Picea engelmannii×glauca) stands in British Columbia. Compared to clearcut scenarios, retained trees reduced regeneration stocking by 0.3–6.5%. The effects on the final yield of the understory cohort ranged from −8 to −32%, depending on the level of retention (2–12m2/ha).