A unified system for tree- and stand-level predictions

Abstract The unified system developed in this study comprises two components, one to predict survival and the other to predict diameter, both at tree and stand levels. The tree survival model defaults to the stand survival model when tree diameter reaches a certain value. Similarly, the tree diameter growth model defaults to the quadratic mean diameter model when tree diameter is equal to quadratic mean diameter. The annual growth approach was used to accommodate growth intervals of different lengths. Parameters of the unified system can be estimated together (Simultaneous Estimation) or separately in two phases (Sequential Estimation). Also investigated was the Disaggregation method in which tree attributes (survival probabilities and diameters) were adjusted to match outputs from the stand-level models (number of trees and basal area per unit area). Results indicated that, overall, the Disaggregation approach gave a better performance than did the Unadjusted approach. On the other hand, the Sequential Estimation narrowly surpassed the Simultaneous Estimation method (overall rank of 1.00 versus 1.10). Parameters of the unified system should be estimated by use of the Sequential Estimation method because it is a simpler method which involves only a subset of the parameters at each estimation phase.