EXTENDED ROTATIONS AND CULMINATION AGE OF COAST DOUGLAS-FIR - OLD STUDIES SPEAK TO CURRENT ISSUES

Trends of mean annual increment and periodic annual increment were exa mined in 17 long-term thinning studies in coast Douglas-fir (Pseudotsu ga menziesii var. menziesii (Mirb.) France) in western Washington, wes tern Oregon, and British Columbia. Maximum ages included ranged from a bout 90 years on high sites to 117 years on a low site. None of the st ands had clearly reached culmination of mean annual increment, althoug h some appeared close; periodic annual increments declined only slowly . Extended rotations combined with increased thinning harvests are pro mising components of any strategy to reduce conflicts between timber p roduction and other forest values. These comparisons indicate that rot ations can be considerably extended without reducing long-term timber production. A major problem in such a strategy is design of thinning r egimes that can maintain some reasonable level of timber flow during a ny transition period.