Quantifying effects of different levels of dispersed canopy tree retention on stocking and yield of the regeneration cohort

Under a variable retention strategy, retained trees contribute to the structural complexity of the subsequent stand, and provide habitat for wildlife and shelter for regeneration and understory vegetation. The effects of retained trees on the stocking and yield of the understory cohort vary by the spatial arrangement of retention (group or dispersed), attributes of retained trees (species, condition, size and frequency), site, and other factors. Accurate growth and yield predictions are not yet readily available for the wide variety of stand structures possible under a variable retention strategy. General effects of retained trees on understory tree development are outlined and various approaches to modeling and simulating the effects of variable retention on final yields are compared. Specific simulations quantified the effects of retained trees on regeneration stocking and future yield for pure lodgepole pine (Pinus contorta Dougl. ex Loud.) and interior spruce (Picea engelmannii Parry × glauca) stands in British Columbia. Compared to clearcut scenarios, retained trees reduced regeneration stocking by 0.3–6.5%. Depending on the level of retention (2–12 m2/ha), the effects on the final yield of the understory cohort ranged from −8 to −32%.