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Impact Evaluation of Weed Biological Control Agents

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Impact Evaluation of Weed Biological Control Agents This document was originally published on the website of the CRC for Australian Weed Management, which was wound up in 2008. To preserve the technical information it contains, the department is republishing this document. Due to limitations in the CRC’s production process, however, its content may not be accessible for all users. Please contact the department’s Weed Management Unit if you require more assistance. #1 Impact evaluation of weed biological control agents What is impact evaluation? Impact evaluation of biological control agents is performed either before or after their release in the introduced range of the target weed. Pre-release impact evaluation is carried out in laboratories and glasshouses or in the field in the weed’s native range Best practice guide practice Best to predict impact of candidate agents on individual plants or populations and to assist in selection of the most promising agents. Post-release impact evaluation measures the effectiveness of agents Post-release impact evaluation is crucial to understanding the overall success rate of a biological in reducing target weed populations • control program. Here the effects of grazing, herbicides and biological control agents (Longitarsus Impact evaluation of weed biological control agents agents control weed biological of evaluation Impact in the introduced range and quantifies echii and Mogulones larvatus) are being monitored on Paterson’s curse. the benefits for associated plant Photo: CSIRO communities, ecosystems, the economy and society in general. program, ultimate success can only and improve efficiency and effectiveness In some instances, the direct effects be demonstrated by undertaking post- of future programs for other weeds. of released agents may be monitored release impact evaluation. Claiming For example, the data gathered may on non-target plant species identified success of a biological control program inform practitioners that other agents as possible hosts during host-specificity without quantitative assessment is affecting different life stages of the tests prior to release: but this is not the questionable because other factors target weed will need to be introduced focus of this guide. such as variation in climate, land use to exert additional stresses on weed and / or management practices may populations or that change in other Why perform post-release have contributed to a weed management practices may increase impact evaluation? population’s decline. agent impact. Rigorous assessment of programs also provides data to Measuring impacts of agents on demonstrate the effectiveness of While confirming establishment, target weed populations can provide biological control and hence justify prevalence and abundance of released the necessary information to fine-tune continued investment in research agents over space and time is a crucial a biological control program’s strategy milestone for any biological control and implementation. Who should undertake necessary data for subsequent analyses. against which effectiveness can be post-release impact Post-graduate student projects are also later evaluated. These targets estimate evaluation? a possible avenue for more theoretical the required decline in weed density intensive studies to be undertaken, (or other population level parameters) The research group that initiates the such as developing an understanding over a defined timeframe to reduce biological control program often takes of the indirect impacts of agents on impact of weed populations below responsibility for post-release impact the ecosystem. Community groups and an economic or ecological threshold. evaluation of agents, but rarely gets state and local government officers For example, a 25% reduction in the continuation of funds necessary may also become involved, particularly weed cover within 10 years may be to undertake long-term evaluation. when monitoring protocols and considered as necessary to obtain Sufficient resources and funding should sampling regimes are simple and not a satisfactory increase of desirable be negotiated and put aside at the too time-consuming. A program can vegetation at infested sites. More start of programs to support at least greatly benefit from such involvement generally, determining the relationship a minimal level of impact evaluation because it increases the number of between a quantitative measure of activities soon after an agent is released. sites monitored at regional scales. the weed population (including per Additional funding should be accessible capita assessment) and the economic later to support long-term monitoring. Prerequisite benchmarks or ecological impacts may be more Multi-disciplinary teams comprising for evaluation helpful because it allows an observed ecologists, entomologists / plant level of decline to be equated to a pathologists, economists and modellers Performance targets defined at the degree of impact and hence benefits. are most effective in devising appropriate beginning of biological control programs Devising such relationships however, monitoring programs to gather the provide quantitative benchmarks requires knowledge of the economic and / or ecological impacts of the weed and what level of control is necessary to ameliorate these impacts. Partnerships between economists, plant ecologists and plant population modellers are recommended to document impacts of the target weed in order to devise realistic performance targets for a program. Such a priori explicit criteria against which agents or programs can later be judged are still rarely made, to the detriment of biological control as a discipline. Economic impact evaluation Cost-benefit analyses are fundamental to evaluating the economic impacts of biological control programs quantitatively. The output of such analyses, expressed as a benefit-cost Impact evaluation of weed biological control agents agents control weed biological of evaluation Impact ratio or as a net present value, is a • measure of the return on investment from the program. A benefit-cost ratio is derived by dividing the value of the losses avoided by affected industries or other stakeholders (in other words what economic damage would have Impact evaluation of the bridal creeper rust fungus (Puccinia myrsiphylli) and responses of associated vegetation. been caused by the weed in the Best practice guide practice Best Photo: Peter Turner absence of the project, including 2 costs for control), by the research and » Define performance targets of development costs of the biological biological control program control program. A net present value » » » » » is an indicator of how much cash value Select appropriate approach to a project adds to the value of the monitor ecological impacts of agents industry concerned. Both costs and benefits are discounted at a specified Determine number of sites and years rate to account for differences in the to monitor Use experience to improve impact time when they were incurred; costs evaluation of current and future biological control programs are up-front while benefits increase Determine parameters (variables) steadily as agents gradually impact to monitor on the weed. Cost-benefit analyses are more robust Implement monitoring schedule when carried out after there has been ample time for the field impact of Analyse and report (publish) results » agents to be realised and sufficient long-term ecological impact data to Figure 1: Key steps for developing a monitoring program to evaluate post-release ecological impacts of biological control agents. be assembled. They are also more Adapted from Roni et al 2005 convincing when based on accurate data on research and development each has pros and cons (Table 1). To be changes in density because they can costs of programs, economic and social most effective, post-release ecological be analysed with high precision using costs of the target weed and its rate impact evaluation should be planned image analysis software. Decrease in of spread and distribution, before and well before any agents are released weed density may not be easily detected after releases of agents. to ensure that crucial pre-release in photographs if other vegetation is Unpriced values for benefits such as measurements are gathered. This replacing the controlled weed and the preservation of native biodiversity includes determining the design, therefore additional information on the guide practice Best and scenic amenity, improved scale and duration of the monitoring type of plants present at photopoints recreational access to land and water, program and the types and timing has to be collated. Photographs also reduction of fire hazard, decreased of data collection (Fig. 1). do not provide evidence that the exposure of environment to herbicides, decline in weed populations is due and costs such as ‘collateral damage’ Approaches to the agent(s), unless it is coupled on non-target plants (if applicable), with an assessment of agent damage are not included in the analysis unless Before- and after-release and density. • Impact evaluation of weed biological control agents agents control weed biological of evaluation Impact a definitive dollar value has been assessments Comparing historical and estimated. Nevertheless, unpriced Photopoints: The simplest and contemporary data: Published and environmental and social benefits and cheapest approach to evaluate impact unpublished historical information, costs should be captured and described of biological control agents is to establish such as field ecological
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