Modelling the rubber tree system

• Main Author: Abd Karim, Yahya
• Other Authors: Buckley, Peter ; Cadisch, Georg ; Edwards, Grant
• Published: Imperial College London 2006
• Subjects: 633.8952
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429388

An effort is made to develop a model that aims to predict the growth and production of rubber under different environmental conditions as well as different agroforestry options. The work begins with the development of the simple static model, namely Hevea Version 1.0, which acts as a precursor for development of a dynamic model. The dynamic model, which was developed using STELLA Research Software Environment and Microsoft EXCEL is then linked to the current agroforestry model WaNuLCAS (Water, Nutrients, and Light Capture in Agroforestry Systems). STELLA is the software for building system models while Microsoft EXCEL provides data analysis, list keeping, calculations as well as presentation tools. Two sub-models were added, namely a Tapping sub-model and a Tapping Panel sub-model, as a part of process to improve the efficiency of the overall model predictions. The model was run for 20 years, representing the economics life of rubber, and the outputs of the simulation were compared with observed data for validation purposes. Results from the statistical analysis showed that the model was able to simulate the girth, latex production, above-ground biomass, leaf and twigs and wood production with efficiencies (EF) of 0.83, 0.97, 0.70, -0.15 and -4.90 respectively. EF measures the accuracy of the model in performing simulation as compared to experimental data. An optimum value of EF is 1. The negative value for leaf and twigs and wood production indicated that the observed mean value is better than predicted value. An economic analysis, based on the output of the dynamic model for different rubber agroforestry system options, showed that the option of planting maize as an intercrop with rubber before tapping, followed by selling rubber wood at the end of a 20-year of rotation gave the highest Net Present Value, Internal Rate of Return, Benefit-Cost Ratio and Annual Equivalent Value compared with the option of planting rubber as monocrop.