Defining the white clover zone in eastern mainland Australia using a model and a geographic information system

A mechanistic model of persistence and production was combined with a geographic information system to define zones of adaptation for white clover (Trifolium repens) within an area encompassing most of the Temperate High Rainfall Zone on the eastern Australian mainland. Using a digital elevation model as co-variate data, monthly climate surfaces for rainfall, rain days, maximum and minimum temperature, evaporation and solar radiation were constructed using the Australian Climate Surfaces and the esoclim program. A broad, subjective zone where white clover could grow was defined by simple logical modelling, and subdivided using factors such as annual rainfall and elevation as threshold constraints. Simulations were run with a white clover model for 91 climate stations having > 2 years of evaporation data. A surface describing annual white clover dry matter production was created by using latitude, longitude, elevation, annual rainfall, January maximum temperature as independent variables in the thin plate spline interpolation routine anusplin. The production map was reclassified in the GIS to define a six-category white clover zone based on the relative magnitude of modelled annual dry matter production. The map produced offers an ecological view of the white clover zone with boundaries based on a better spatial representation of climatic constraints.