© 2005 Heron Publishing—Victoria, Canada
Evaluating the accuracy and generality of a hybrid patch model
Rupert Seidl (1), Manfred J. Lexer (1, 2), Dietmar Jäger (1) and Karl Hönninger (1)
1. University of Natural Resources and Applied Life Sciences (BOKU) Vienna, Department of Forest and Soil Sciences, Institute
of Silviculture, Peter Jordan Straße 82, 1190 Vienna, Austria / 2. Corresponding author (mj.lexer@boku.ac.at) / Received June 1, 2004; accepted March 19, 2005; published online May 2, 2005
Summary
Forest patch models have been used extensively to simulate vegetation development under current and changing environmental
conditions. However, their physiological foundation is subject to criticism and recent validation experiments against long-term
growth and yield data have shown major deficiencies in reproducing observed growth patterns of mixed-species forests. Here
we describe the modified forest patch model PICUS Version 1.3, a model variant that couples the structurally detailed three-dimensional
patch model PICUS Version 1.2 and the physiologically based stand-level production module of the 3-PG (Physiological Principles
in Predicting Growth) model. The approach attempts to combine the ability of PICUS v1.2 to simulate forest dynamics on time
scales relevant to forest succession with a simplified but successful production model based on the concept of radiation-use
efficiency. We evaluated the hybrid model in a series of simulation experiments. Results indicated a realistic response to
a climate sensitivity experiment: the response to environmental gradients was well captured both in terms of productivity
on time scales of a rotation length and of forest succession over several hundreds of years. Testing against independent long-
term growth and yield data revealed good correspondence between observed and predicted values of volume production and stand
structure. Further model development should include a dynamic soil component to consider effects of nutrient cycling.
Keywords:
3-PG, model coupling, PICUS, productivity, species composition, validation.
