1. General Model Information
Name: HyPAR: A mechanistically-based agroforestry model
Main medium: air+terrestrial
Main subject: agriculture, forestry, hydrology, biogeochemistry
Organization level: ecosystem
Type of model: not specified
Keywords: agroforestry, Hybrid, PARCH, semi-arid tropics, overstorey, leaf area index, water use efficiency, competition, sorghum
Deena C. Mobbs,
Institute of Terrestrial Ecology,
Bush Estate, Penicuik, Midlothian EH26 0QB, UK
Tel: 0131 445 4343/6
D. C. Mobbs; M.G.R. Cannell; GJ. Lawson; N.M.J. Crout
HyPAR (v.2.7) is developed by taking a 'generic' approach, modelling a simple, theoretical
agroforestry system, by combining an existing tree/forest model (
Hybrid) with a
dryland tropical crop (sorghum) model
A generic modelling approach
Generic models are built from first principles, and capture only the essential elements
of a problem. The problem here was to explore the climatic boundary conditions where total site
production (of trees and crop) might be increased by growing trees, without severely depressing
crop yields. The limiting resources were defined as light and water. The essential elements were
therefore: (i) an overstorey tree model which could calculate annual net primary production
(NPP) as a function of daily weather, requiring a physiologically-based model including light
interception, tree water balance, photosynthesis, stomatal conductance and maintenance
respiration; (ii) a crop model, appropriate for semi-arid regions (we chose sorghum), which could
predict potential harvested yield as a function of daily weather beneath the trees; and (iii) a soil
model which represented vertical soil water movement and status, and water capture by tree and
The resulting theoretical generic model must give realistic estimates of tree and crop
production as a function of daily light and water use. However, unlike a simulation model, it is
not possible to reproduce observations at the plot level, as these depend on factors not
represented in the model, such as nutrient cycling. The purpose of the model is to
help to define biophysical boundary conditions.
The simple model system
An overstorey of `generic' broadleaved tropical trees was assumed to occupy a plot
throughout the year. In standard runs, the canopy was assumed to be spatially
homogeneous and to have a constant leaf area index (LAI) throughout the year.
Similarly, tree fine roots were assumed to be spatially homogeneous and present
throughout the year, but to penetrate to deeper soil layers than crop roots.
Daily net photosynthesis, transpiration and maintenance respiration by the trees were
calculated to give annual NPP. Water was extracted from the rooting zone according to
transpiration demand, soil water availability and root length density, which decreased
exponentially with depth (Jonsson et al., 1988).
One sorghum crop (cultivar CSH-6) was sown at the start of the rains each year
beneath this overstorey canopy. The solar radiation it received was that transmitted
through the tree canopy (the trees were always taller than the crop), rainfall was
throughfall, and soil water was shared with the trees (see below). The crop roots grew
dynamically into the soil occupied by tree roots. Daily crop dry matter production and
transpiration were calculated, and the crop grew to harvest according to a phenological
timetable with a final potential grain yield.
Strengths and limitations of the model:
The strengths of this simple model system were that:
The limitations were that:
- transpiration and assimilation, and hence the use of water and light, were coupled
in both the overstorey and the crop, and between the two components;
- tree NPP and potential crop grain yield were calculated from daily climate; and
belowground competition for water was represented.
"Some of these limitations are being addressed in future versions of the model, but we
believe that the model in its present form has given valuable and clearly interpretable
output"(Cannell et al.,1997).
- nutrients were not represented;
- tree canopy and roots were spatially homogeneous;
- tree growth is based on a yearly timestep;
- air temperatures and humidities were the same for the trees and crop; and
- the crop was limited to sorghum and to one crop per year.
Source of abstract: D.C.
Mobbs et al. 1998 (60K, .pdf download file)
II. Technical Information
III. Mathematical Information
Mobbs, D.C.; Lawson, G.J., Brown, T.A.W.; Crout, N.M.J.; Hodnett, M.G. & Friend, A.D. 1998. The HyPAR User Guide, Version 2.7, November 1998. 120p. ITE: Edinburgh
Mobbs, D. C., Cannell, M. G. R., Crout, N. M. J., Lawson, G. L., Arah, J. and Friend, A. D., 1998. Complementarity of light and water use in tropical agroforests. I Model outline, performance and sensitivity. Forest Ecology and Management 1998, 102: 2-3, 259-274; 40 ref..
Cannell, M.G.R.; Mobbs, D.C. and Lawson, G.J. 1998. Complementarity of light and water use in tropical agroforests. II. Modelled theoretical tree production and potential crop yield in arid to humid climates. Forest Ecology and Management 1998, 102: 2-3, 275-282; 20 ref..
Lott, J.E., Black, C.R. & Ong, C.K. 1998 Comparison of output from HyPAR with observed maize yields in CIRUS.Report to DFID-FRP from Nottingham University (R5810). 45p. Sutton Bonnington.
Lawson, G.J. & Mobbs, D.C. 1998.Carbon allocation in individual tree models: a literature review and description of recent modifications made to the HyPAR model. In: Combined growth and water use modelling of mixed vegetation. Centre for Ecology and Hydrology Project T6050P2, 23p, Wallingford
Mobbs, D.C.; Lawson, G.J.; Cannell, M.G.R. & MacDonald, K.J. 1997. Light Interactions in the HyPAR ModelIn: Agroforestry Modelling and Research Co-ordination, Annual Report to ODA July 1996 - June 1997; Institute of Terrestrial Ecology: Edinburgh, UK
Crout, N.M.J. 1997. Nutrient relationships in the HyPAR model In: Agroforestry Modelling and Research Co-ordination, Annual Report to ODA July 1996 - June 1997; Institute of Terrestrial Ecology: Edinburgh, UK
Mobbs, D.C.; Crout, N.M.J.; Lawson, G.J.; Cannell, M.G.R. 1997. Structure and applications of the HyPAR model. Special issue on agroforestry modelling: selected papers from a workshop held in Edinburgh, 28-30 May 1997. Agroforestry Forum. 1997, 8: 2, 10-14; 6 ref..
Lawson, G.J. & MacDonald, K.J. 1996. Approaches to modelling the interception of radiation in discontinuous canopies. In: Agroforestry Modelling and Research Co-ordination. Annual report to ODA June 1995 - May 1996, 73-90. ITE: Edinburgh
Mobbs, D.C.; Cannell, M.G.R. 1995. Optimal tree fallow rotations: some principles revealed by modelling. Agroforestry-Systems.1995, 29: 2, 113-132; 24 ref..
Lawson, G.J.; Crout, N.M.J.; Levy, P.E.; Mobbs, D.C.; Wallace, J.S.; Cannell, M.G.R.; Bradley, R.G.; Sinclair, F. 1995. The tree-crop interface: representation by coupling of forest and crop process-models. Agroforestry: science, policy and practice.Selected papers from the agroforestry sessions of the IUFRO 20th World Congress, Tampere, Finland, 6-12 August, 1995. Agroforestry-Systems. 1995, 30: 1-2, 199-221; 29 ref..
Friend, A.D.; Stevens, A.K.; Knox, R.G. and Cannell, M.G.R., 1997. A process-based, biogeochemical, terrestrial biosphere model of ecosystem dynamics (Hybrid v3.0). Ecol. Modelling 95: 249-287.
Friend, A.D., 1997. Parameterization of a global daily weather generator for terrestrial ecosystem and biogeochemical modelling. Ecol. Modelling (in press).
Friend, A.D., 1995. PGEN: an integrated model of leaf photosynthesis, transpiration and conductance. Ecol. Modelling 77: 233-255.
Bradley, R.G. and Crout, N.M.J., 1994. PARCH - User Guide. Tropical Crops Research Unit, University of Nottingham, Sutton Bonington, Leicestershire, UK. 122pp.
Bradley, R. G., Crout, N. M. J. and Azam-Ali, S. N., 1996. PARCH: A model for the growth and yield of sorghum: 2. Validation of yield and biomass predictions. Submitted to J. Agric. Sci.
Ong, C. K.; Black, C. R.; Marshall, F. M. and Corlett, J. E., 1996. Principles of resource capture and utilisation of light and water. In: Tree-crop interactions - a physiological approach. Eds C. K. Ong and P. A. Huxley. CAB International.
Gregory, P., 1996. Growth and activity of tree roots - the key to understanding agroforestry? Agroforestry Forum 7, 4-6. Bangor, UK.
Conijn, J.G., 1995. RECAFS: a model for resource competition and cycling in agroforestry systems. Rapport No 12. Production Soudano-Sahelienne. AB-DLO, Wageningen, Netherlands.
Huxley, P. A., 1994. Root systems of some tree species and implications for resource capture in agroforestry. In: Resource capture by crops. Eds J. L. Monteith, R. K. Scott and M.H. Unsworth. p 409-410. Nottingham University Press, UK.
V. Further information in the World-Wide-Web
VI. Additional remarks
Last review of this document by: J. Bierwirth Thu Dec 10 15:19:44 MET 1998
Status of the document:
last modified by
Tobias Gabele Wed Aug 21 21:44:44 CEST 2002