Volume Growth Trends in a Douglas-Fir Levels-of-Growing-Stock Study

Mean curves of increment and yield in gross total cubic volume and net merchantable cubic volume were derived from seven installations of the regional cooperative Levels-of-Growing-Stock Study (LOGS) in Douglas-fir. The technique used reduces the seven curves for each treatment for each variable of interest to a single set of readily interpretable mean curves. To a top height of 100 ft and corresponding average age of 45 years, volume growth and yield are strongly related to stocking level, being highest at the highest stocking levels. At that point, current annual increment is still far greater than mean annual increment. Thinning has accelerated diameter growth of the largest 40 trees per acre as well as of the stand average. Maximum volume production would be obtained at stand relative densities approaching the zone of competition-related mortality, although in practice considerations of feasibility of frequent entries and wildlife and amenity considerations would make somewhat lower average levels necessary. West. J. Appl.