Constraining individual tree diameter increment and survival models for loblolly pine plantations

Abstract

Among extant forest growth and yield models, individual tree growth models provide the most detailed information, which is useful for intensive forest management. However, individual tree growth models may be inaccurate for stand-level predictions because of the cumulative error resulting from individual tree predictions. This paper is aimed at developing a method to ensure that individual tree growth models not only provide precise individual tree predictions but also give precise stand-level estimation. Based on the conceptual relationships between basal area of each diameter class and the diameter increment of trees in the same diameter class, a constrained regression equation system is proposed. The same approach is also applied to modeling individual tree survival probability. An algorithm for estimating multiresponse regressions was developed. Results using data from unthinned loblolly pine (Pinus taeda L.) plantations show that the simultaneous equation system provides nearly the same individual tree diameter increment estimates as the unconstrained model but better estimates for basal area of each diameter class and for total stand basal area. The potential for improving stand mortality estimation with a constrained individual tree survival model where there is little mortality in the data is limited.