1. General Model Information

Name: Model of resource competition in cassava-based agroforestry systems

Acronym: HYCAS

Main medium: terrestrial
Main subject: agroforestry
Organization level: ecosysystem
Type of model: not specified
Main application:
Keywords: cassava, Manihot esculenta, agroforestry, Hybrid, GUMCAS


Robin B. Matthews
Lecturer in Agroecological Modelling
Department of Natural Resources Management,
Cranfield University, Silsoe,
Bedfordshire MK45 4DT,
United Kingdom.
Tel: +44 (0) 1525 863008
Fax: +44 (0) 1525 863384
email: r.b.matthews@cranfield.ac.uk


Robin Matthews


Cassava (Manihot esculenta L. Crantz) is an important energy source in the diet of people in the tropics; recent estimates suggest that its storage roots provide 8% or more of the minimum calorie requirement for more than 750 million people . Moreover, the crop is often grown in association with trees and other crops in agroforestry systems; in Brazil, it is often grown with perennials such as cocoa and rubber, in Malaysia with rubber in the first 2-3 years, and in India with coconut.

As a means of understanding the complex competitive interactions in such systems, a model describing the dynamics of resource capture and use by the components of a tree/cassava agroforestry system was developed by combining the Hybrid tree model with the GUMCAS cassava model.

Model Structure:
Both Hybrid and GUMCAS models are process-based, and run on a daily time-step. The combined HyCAS model takes into account interactions between the trees and the crop for light, water and nitrogen.
The amount of light intercepted by the tree canopy (assuming a horizontally uniform leaf area distribution) is subtracted from overall incident solar radiation to calculate the amount of light reaching the crop.
Modification of crop temperatures is not considered at present.
Water uptake by each species is calculated using the GUMCAS routines , assuming that the root inflow rates (cm3 water (cm root)-1) are the same for both tree and crop for a given soil water content. Thus, the competitive ability for water of each species is determined by the relative size of its root system only.
Nitrogen uptake by each species is described by first calculating the `demand' required to maintain tissue N contents (g N (g DM)-1) at set levels, and then calculating the ability of the soil and root system to supply N, again assuming the root inflow rates for N are the same for each species. Actual N uptake is taken as the minimum of these two values. Thus, as with water, competitive ability for N is determined by the relative sizes of the root systems.

Source of abstract: HyCAS Model homepage, Cranfield University

II. Technical Information

II.1 Executables:

Operating System(s):

II.2 Source-code:

Programming Language(s):

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

Matthews, R.B. & G J Lawson, 1997a. Structure and applications of the HyCAS model- Summary of Proceedings of 3rd DFID (ODA) Agroforestry Modelling Workshop, Newbattle Abbey, Edinburgh, 28-29 May 1997.
Matthews, R.B. & G J Lawson, 1997b. Structure and applications of the HyCAS model- Chapter 6 in Agroforestry Modelling Project Annual Report, June 96-July 97.
Matthews, R.B. & G.J. Lawson, 1997c. Structure and applications of the HyCAS model. Agroforestry Forum 8(2):14-17.
Matthews, R.B. 1998.Modelling phosphorus dynamics of cassava-based agroforestry systems. Final Report of Sub-contract to DFID Project R6348, Agroforestry Modelling Project.

V. Further information in the World-Wide-Web

VI. Additional remarks

Last review of this document by: Juergen_Bierwirth Mon Dec 14 17:35:48 CET 1998

Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:44 CEST 2002

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