Comparison of outputs of a biophysical simulation model for pasture growth and composition with measured data under dryland and irrigated conditions in New Zealand

Abstract

AbstractSimulation models have a role in predicting and understanding the consequences of weather and management perturbations to biophysical systems. One such model is EcoMod – a biophysical simulation model of a pastoral ecosystem. It comprises a range of sub‐models that form the main components of pastoral ecosystems – namely plants, soils and ruminant livestock. These component models are integrated to simulate the complex interactions occurring within such systems. The purpose of this study was to test how well EcoMod simulated the changes in growth rate and plant composition of dryland and irrigated pasture production in a temperate climate through comparison with a long‐term (1966–2003) data set measured in New Zealand. The general behaviour of the modelled pastures was similar to those of the observed pastures. There was also close agreement between the measured and modelled total annual and monthly growth rates of dry matter (DM), particularly after modifying some of the parameters of plant growth to better represent the characteristics of dominant species present under dryland and irrigation pastures. There was greater discrepancy between measured and modelled pasture composition but in the case of the simulation of the dryland pasture, the proportional differences in species composition were much greater than the absolute differences in species composition. In addition to comparing the outputs of EcoMod to data from actual pasture production, model testing issues and potential sources of error between model outputs and data were also examined.