Complementarity of light and water use in tropical agroforests I. Theoretical model outline, performance and sensitivity.
1998
Mobbs, D. C. | Cannell, M. G. R. | Crout, N. M. J. | Lawson, G. J. | Friend, A. D. | Arah, J.
Agroforestry models are needed to help define the biophysical boundary conditions where agroforestry may be beneficial. A generic, process-based model is outlined which couples light and water use in a tree-crop-soil system, focusing on ability of trees to enhance production in regions where water is limiting. The model predicts the net primary production (NPP) of a uniform overstorey of tropical broadleaved trees, using parts of the model Hybrid v3.0 (Friend, A.D. et al. (1997) Ecological Modelling 95, 249-287) and the growth and grain yield of an understorey sorghum crop, modelled using the resource capture crop model PARCH. Below-ground competition for water is simulated. The model is driven by daily climate, which can be generated for any half-degree pixel in the world. The performance of the model is illustrated for a site in Ghana. The model gives validated output of the NPP of natural forest/woodland vegetation and of potential sorghum grain yield. Tests of the sensitivity of the model to simplifying assumptions are presented and discussed. It is concluded that the model provides a useful tool to explore opportunities for complementarity of light and water use by trees and sorghum in a range of climates. The following paper (Cannell, Mobbs & Lawson Forest Ecology and Management 102 pp. 275-282) uses the model to explore the climatic boundary conditions for agroforestry with respect to rainfall.
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