Fitting process-based models with stand growth data: problems and experiences

A process-based growth model (PBM) for even-aged stands is presented which is based on photosynthesis relationships and provides predictions in terms of tree dimensions. The model has been simplified with only the most essential aspects of photosynthesis, physiology, and tree structure included. As a result, the model has fewer parameters than a typical PBM. Some of these parameters are aggregation of physiological and biometrical constants and thus summarize the effect on stand growth of many PBM parameters. Problems arising in estimating the parameters of a PBM are discussed, using the present model as an example. Finally, an example of calibrating the present model for different sites using typical measurements of stand growth is presented.