© 2000 Heron Publishing—Victoria, Canada
Application of volume growth and survival graphs in the
evaluation of four process-based forest growth
models
Annikki Mäkelä (1), Risto Sievänen (2), Marcus Lindner (3) and Petra Lasch (3)
1. Department of Forest Ecology, P.O. Box 24 (Unioninkatu 40), FIN-00014, University of Helsinki, Helsinki,
Finland (annikki.makela@helsinki.fi) / 2. Finnish Forest Research Institute, Vantaa Research Centre, Vantaa, Finland / 3. Potsdam Institute for Climate Impact Research, P.O. Box 60 12 03, 14412 Potsdam, Germany / Received October 22, 1998
Summary
Volume growth and survival (VGS) graphs, which show volume growth rate and risk of mortality for individual trees (or tree
size classes), have been proposed as a tool for assessing the validity of models that describe the development over time of
tree size distributions within forest stands. We examined the utility of the VGS method in evaluating four process-based models.
The performance of the models FORSKA, 4C, MORG, and PipeQual is analyzed against long-term data from a Scots pine stand in
Evo, Finland, and the models FORSKA and 4C are also assessed with respect to data from a beech stand in Fabrikschleichach,
Germany. Comparison of the measurement-based VGS graphs with those produced from the model-based data shows that although
the models yield similar stand-level predictions, they can differ widely in their projections of individual tree growth and
size distributions. Examination of the discrepancies between models and data in the context of the VGS graphs reveals several
areas in which the models could be improved. We conclude that the method is useful in model evaluation, especially if used
in combination with indicators of stand structure, such as the height/diameter ratio.
Keywords:
model evaluation, size distribution, Pinus sylvestris, Fagus sylvatica, stand structure, permanent sample plot.
