A comparison of forest gap models: Model structure and behaviour |
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| Authors: | Harald K M Bugmann Xiaodong Yan Martin T Sykes Philippe Martin Marcus Lindner Paul V Desanker Steve G Cumming |
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| Institution: | (1) Department of Global Change and Natural Systems, Potsdam Institute for Climate Impact Research, P.O. Box 601203, D-14412 Potsdam, Germany;(2) Institute of Applied Ecology, Academia Sinica, P.O. Box 417, Shenyang, People's Republic of China;(3) Department of Plant Ecology, Lund University, S-22361 Lund, Sweden;(4) Institute for Remote Sensing Applications, CEC Joint Research Centre, I-21020 Ispra, VA, Italy;(5) School of Forestry and Wood Products, Michigan Technological University, 1400 Townsend Drive, 49931 Houghton, MI, USA;(6) Department of Forest Sciences, University of British Columbia, V6T1Z4 Vancouver, B.C., Canada |
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| Abstract: | Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models.As examples of qualitative model comparisons, the different formulations used for the heightdiameter relationship, for the maximum growth equation, and for the effects of temperature and drought on tree growth are reviewed. The variety of formulations currently in use has the potential to influence simulation results considerably, but we conclude that little is known on the sensitivity of the models in this respect.The quantitative model comparisons performed so far allow us to draw the following conclusions: (1) Gap models are quite sensitive to the formulation of climate-dependent processes under current climate, and this sensitivity is even more pronounced under a changed climate. (2) Adaptations of forest gap models to specific regions have required detailed sub-models of species life history, thus complicating model comparison. (3) Some of the complex models developed for region-specific applications can be simplified without hampering the realism with which they simulate species composition. (4) Attempts to apply the models without modification beyond the area for which they were developed have produced controversial results.It is concluded that the sensitivity of forest gap models to the exact process formulations should be examined carefully, and that more systematic comparisons of model behaviour at a range of test sites would be desirable. Such studies could improve our understanding of forest dynamics considerably, and they would help to focus future research activities with gap models. |
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