GREEN-TREE RETENTION - CONSEQUENCES FOR TIMBER PRODUCTION IN FORESTS OF THE WESTERN CASCADES, OREGON

National Forest management in the Pacific Northwest is adopting ecosys tem management, in which the entire forest ecosystem is considered, as well as commodity production. Silvicultural prescriptions in ecosyste m management often include retention of some live trees following timb er harvest (green-tree retention) with the primary goal of maintaining biodiversity. How green-tree retention will affect growth and tree sp ecies composition of future forests is an important question. We took a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. We used United States Department of Agriculture (USDA) Forest Service timber inventory plot data from the Cascade Mountains of Oregon and southwest Washington (western hemlock zone). We selected 132 unmanaged stands w ith a tree cohort of 70-110 yr old (regeneration) or a tree cohort of 70-110 yr old with an overstory of large trees 200+ yr old (remnants), representing clearcuts and stands harvested with green-tree retention , respectively. Regeneration basal area (BA) across species and for Ps eudotsuga menziesii tended to decline with increasing remnant density (R(2) = 0.51 and 0.60, respectively), but only after remnant densities reached approximate to 15 trees/ha; the relationships were roughly si gmoidal. Part of the effect of remnants on regeneration results from r emnants' occupation of space, making it unavailable to the regeneratio n. After adjusting regeneration BA to account for remnants' space occu pation, the relationship between regeneration BA and remnant density w eakened by about half, implying that remnant effects resulted from bot h space occupancy and other factors associated with remnants. Total-st and BA was relatively constant across remnant densities. Remnant densi ty was not related to tree-species diversity in the regeneration.