Towards a nationwide growth and yield model for radiata pine plantations in New Zealand

Abstract

A study was designed to evaluate a forest stand modelling approach for management use that can be applied across a wide range of site types and climatic regions. Radiata pine (Pinus radiata D. Don) plantations dominate New Zealand's forestry sector; thus, this species was the subject of the study. A major goal of the study was to compare different modelling approaches, which combine simplicity and site sensitivity. Therefore, two general modelling approaches were investigated: a site-stratified and a physiological hybrid approach. Both approaches were implemented by using difference equations. The investigation revealed more consistently improved fits of stratified models, although the fitting process showed potential bias of parameter estimates. On the other hand, the hybrid approach resulted in promising results, especially for stand basal area. The introduction of climate and site variables showed less improvement for mean top height than for basal area. The application of the model on regional scales resulted in an improved prediction in a region with plenty of growth limitations, but less precise results in a region where growth was limited primarily by light and temperature. In the whole, results of the hybrid approach will encourage further studies that incorporate more sophisticated approaches for depicting physiological processes.