A bioeconomic model of Californian thistle in New Zealand sheep farming

Abstract

Control of weeds, particularly pasture weeds, may be important to New Zealand agriculture. However, the impact is hard to assess because there is limited information on the range of weed species and the rates of infestation. Existing estimates suggest that the economic impacts run to hundreds of millions of dollars, if not more, and this is supported by the relative figures estimated in overseas research. The present research has developed a bioeconomic model for weed management. Computer modelling is useful because the behaviours of weed populations on farms and in other areas are affected by complex linkages with human activities and non human species. The model was calibrated on the impacts of Californian thistle (Cirsium arvense) in intensive, lowland sheep pastures in New Zealand, and can be extended to model other weeds and products. Californian thistle is known to be a significant weed for these farms, and this part of the sheep sector accounts for some 17.1 million head out of a national flock of 39.9 million. There are three main outputs from this research. Firstly, it provided an estimate of the economic value to the sheep sector of biocontrol of Californian thistle. Secondly, the research demonstrated the value and feasibility of bioeconomic modelling for analysing agricultural production systems. Thirdly, the project found key gaps in information about actual impacts of Californian thistle, including the amount of area affected and the level of infestation.