Ecological forestry in an uneven-aged, late-successional forest: simulated effects of contrasting treatments on structure and yield.

摘要

Ecological forestry practices are designed to retain species and structural features important for maintaining ecosystem function but which may be deficient in conventionally managed stands. We used the spatially-explicit, individual tree model CANOPY to assess tradeoffs in enhanced ecological attributes vs. reductions in timber yield for a wide variety of treatments in uneven-aged, late-successional northern hardwood forests. Treatments included various combinations of (1) larger retained maximum tree diameters in the post-harvest stand, (2) permanently reserved legacy trees, (3) variable opening sizes, (4) coarse woody debris retention, (5) species harvest restrictions, and (6) occasional moderate-intensity harvests with larger openings ('irregular multi-cohort harvests'). Compared to conventional single-tree selection, reduction in simulated harvest yields varied widely from a 9% decline with 7 reserve trees/ha to a 55% reduction in treatments that retained coarse woody debris along with a maximum residual live-tree diameter of 80 cm. Despite the dominance by shade-tolerant species, simulated declines were similar in magnitude to those predicted or observed for relatively shade-intolerant conifers of the Pacific Northwest. Treatments that protected 'sensitive' species from harvest or raised the maximum residual diameter to 80 cm appeared to have the best balance between fostering ecological values of old-growth forests and moderating the impact on timber yield. These treatments produced stands meeting minimum structural criteria of old-growth forests while causing harvest declines of 27-30% compared to conventional single-tree selection. Coarse woody debris volumes were similar to those produced by the reserve-tree treatments, but the species-protection and 80 cm treatments had higher densities of large trees, and there was less reduction in yield for each large tree retained in the residual stand. Most other treatments maintained mature forest structure or stands that vacillated between mature and borderline old-growth conditions.