Modelling the impact of native pastures to examine the relative effects of land use change

This paper describes (1) the development and validation of a native pasture model that accounts for species abundance, (2) the integration of the native pasture model into a catchment framework and (3) the likely biophysical trade-offs associated with increasing the proportion of native perennial pasture species within a pilot catchment. The rationale for developing the model was to build on the conceptualisation of contemporary pasture models and include new algorithms that better represent native grass species commonly found in temperate climate regions of Australia. The native pasture model is phenologically based and simulates both daily pasture growth and soil water dynamics. It was developed and validated against data from field experiments conducted at Wagga Wagga in NSW, Australia, for two native grass species, Austrodanthonia spp. (winter dominant C3) and Bothriochloa macra (summer dominant C4). The model predicted seasonal pattern and inter-annual variation of soil moisture contents and green leaf area
index (GLAI) for various planting densities. There was a high correlation between the simulated and measured soil moisture contents (r 2 = 0.81, p < 0.0001 for Austrodanthonia spp; r 2 = 0.73, p < 0.0001 for Bothriochloa macra) and GLAI (r 2 = 0.66, p < 0.0001 for Austrodanthonia spp; r 2 = 0.83, p < 0.0001 for
Bothriochloa macra) at actual measurement dates.