On the risk of extinction of a wild plant species through spillover of a biological control agent: analysis of an ecosystem compartment model

Invasive plant species can be controlled by introducing one or more of their natural enemies (herbivores) from their native range; however such introduction entails the risk that the introduced natural enemy will attack indigenous plant species in the area of introduction. The effect of spillover of a natural enemy from a managed ecosystem compartment (agriculture) in the area of introduction to a natural compartment (non-managed) in which an indigenous plant species is attacked by the introduced natural enemy, whereas another indigenous plant species, which competes with the first, is not attacked, has been studied. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, the authors have determined model parameters that characterize the risk of extinction. The findings point to the importance of spillover and the relative attack rates (specificity) of introduced natural enemies with respect to target and non-target plant specie

Management strategies for an invasive weed: a dynamic programming approach for Californian thistle in New Zealand

Invasive plants can cause significant problems in natural and agricultural ecosystems. Although research has already been conducted on the economics of a single-control option for some invasive weeds, we extended the analysis by developing a dynamic optimisation model that evaluates the net benefits of a range of possible control options simultaneously in order to identify the optimal strategy (mix of control options). This paper focuses on Californian thistle (Cirsium arvense) in pasture in New Zealand. The net benefit is maximised by considering the costs and efficacy of control options, and the monetary value of animal production. Trajectories of shoot density are developed and the optimal strategies are found. Our results suggest that the introduction of a biological control agent (Apion onopordi), in combination with one or more control options, is the optimal strategy when the initial density of the thistle population exceeds 1.0 shoot m(-2). Results show that in the setting of the model excluding MCPA, MCPB and a Sclerotinia sclerotiorum-based mycoherbicide reduces the net present value (NPV) by less than 2%

Management strategies for an invasive weed: a dynamic programming approach for Californian thistle in New Zealand

Invasive plants can cause significant problems in natural and agricultural ecosystems. Although research has already been conducted on the economics of a single-control option for some invasive weeds, we extended the analysis by developing a dynamic optimisation model that evaluates the net benefits of a range of possible control options simultaneously in order to identify the optimal strategy (mix of control options). This paper focuses on Californian thistle (Cirsium arvense) in pasture in New Zealand. The net benefit is maximised by considering the costs and efficacy of control options, and the monetary value of animal production. Trajectories of shoot density are developed and the optimal strategies are found. Our results suggest that the introduction of a biological control agent (Apion onopordi), in combination with one or more control options, is the optimal strategy when the initial density of the thistle population exceeds 1.0 shoot m(-2). Results show that in the setting of the model excluding MCPA, MCPB and a Sclerotinia sclerotiorum-based mycoherbicide reduces the net present value (NPV) by less than 2%

A Model-based Approach for Determining Optimal Lime Application Rate and Frequency

Soil acidification reduces land productivity across agricultural systems worldwide. The standard remedy is to periodically apply lime to the soil surface which, over a number of years, is assimilated into the soil profile and raises soil pH. Lime applications can be viewed as an investment in soil productivity. This paper presents a dynamic model to determine an optimal lime application for a cereal crop. The results for the Western Australian Wheatbelt using wheat as an indicator of soil productivity, show that optimal application rate and frequency vary with rainfall and initial soil pH. Incorporating lime through the soil profile increases net present value by up to 6% compared to traditional surface lime applications and reduces lime application rates and required time for soil acidity amendment