A COMPARISON OF STAGE–STRUCTURED AND SINGLETREE MODELS FOR PROJECTING FOREST STANDS

Abstract

A stage–structured model for stand management is presented and compared with the structure of singletree simulators. In contrast to single–tree simulators which project the dimensions of each tree in a list that describes the stand, stage–structured models project the movement of trees between predefined diameter classes that are further described by fixed levels of tree height, volume and crown area. A stage–structured model for white–fir is constructed using growth equations from the California Conifer Timber Output Simulator. Both models are used to project yields by product class and time period in managed and unmanaged stands. A comparison of these projections reveals that both simulators make nearly the same projections of total stand volume. The stage–structured model, however, produced different volume yields by product class. The differences appear to be within the accuracy range demonstrated by single–tree simulators. These results suggest that, in a management context, stage–structured models and single–tree simulators predict stand productivity and evaluate alternative management regimes with the same degree of accuracy. Stage–structured models, however, are much more compact and are more easily embedded in numerical optimization algorithms for the analysis of stand management problems.