The bitou bush ('Chrysanthemoides monilifera' subsp. 'rotundata' (DC.) T.Norl.) Threat Abatement Plan (TAP) aims to reduce the impacts of bitou bush on biodiversity in New South Wales. This is the first weed TAP in Australia and so its effectiveness in conserving threatened biodiversity, as well as its cost of implementation, must be examined to determine if this new approach should be adopted as a template for managing the biodiversity impacts of other major weed species. We therefore consider the question 'is the TAP a good investment in relation to protecting biodiversity'? We combine the costs of implementing the TAP with conservative, published estimates of the benefits of protecting biodiversity, to calculate the benefit-cost ratios of the investment. The ratios indicate that the benefits of the TAP exceed the costs under a wide range of economic conditions. While this result supports the approach, the cost of implementation should be analysed over the five years relative to the biodiversity outcomes in order to determine the ex post benefit of the TAP.

1. - Weeds have a wide variety of impacts on society, theenvironment and the economy. Some of the economicimpacts are benefits but most are costs.2. - The costs of particular weeds in given areas have beenestimated by many writers in a rich literature on theassessment of the impacts in agriculture. Only Combellack(1987) has attempted to estimate the nationwide impactof weeds in general.3. - In his innovative study, Combellack valued the economiccosts of weeds in 1981–82 to be $2,096m. New methodsof weed control and techniques of farm managementhave since been developed, and new weed species nowoccur. Therefore the current costs of impacts cannot bereadily compared with those of 1981–82.4. - The nationwide impact of weeds needs to bere-estimated to provide a more recent benchmark thatreflects current costs, prices and technologies, and thecurrent distribution of impacts within the community.A current estimate provides useful information fordecisions on the allocation of resources, cost sharing,and management of specific weed problems.5. - In this report, we attempt to estimate the economiccosts of weeds across Australia. In addition, we offer aneconomic framework to help consider the problems thatweeds create, and the generation and use of informationto resolve those problems.

Government funding to protect native plant communities is usually limited. For cost effectiveness, priority sites for conservation must therefore be identified and funds allocated to protect these sites according to the quantity of communities conserved per dollar of cost. In 1999, invasion of coastal vegetation in New South Wales (NSW) by bitou bush was listed as a key threatening process under the NSW 'Threatened Species Conservation Act' 1995. In accordance with the Act, a Threat Abatement Plan (TAP) was prepared to reduce the impacts of the weed to threatened biodiversity at priority sites. In the present study, data collected for the TAP were analysed by linear programming to determine the feasibility of achieving cost effectiveness in identifying sites and allocating funds, and to explore the impact of associated economic issues on the quantity of native plant communities that are protected. In addition to the total funds and costs per site, the quantity was influenced by alternative funding policies and different site selection strategies. Allocations that recognise these issues can enhance protection outcomes, and promote the cost effectiveness of weed management.

Valuation of the gains from protection of biodiversity is difficult because the services that provide the benefits do not normally pass through markets where prices can form. But the services sometimes pass through markets where consumers or producers behave in a market-oriented manner, and so the values implicit in this behaviour can be identified and derived. Estimates of the benefits of biodiversity protection are derived from the costs of protecting native plant communities from a major weed in Australia, by following this approach. In 1999, invasion of coastal areas of New South Wales by bitou bush (Chrysanthemoides monilifera subsp. rotundata (DC.) T. Norl.) was listed as a key process threatening native plants under the NSW Threatened Species Conservation Act 1995. In accordance with the Act, the Department of Environment and Climate Change prepared a Threat Abatement Plan (TAP) to reduce the impacts of bitou bush on biodiversity at each threatened site. The costs of protecting sites vary closely with the number of priority native species and communities at each site. Following standard economic assumptions about market transactions, these costs are interpreted to provide values the benefits of protecting extra species, communities, and sites. Key words: Bitou bush, Chrysanthemoides monilifera, threat abatement plan, valuation of biodiversity, benefit-cost analysis, weed control, defensive-expenditure method.

The NSW Bitou Bush Threat Abatement Plan (TAP) aims to reduce the impacts of bitou bush on biodiversity in New South Wales. This is the first weed TAP in Australia and so its effectiveness in conserving threatened biodiversity, as well as its cost of implementation, must be examined to determine if this new approach should be adopted as the template for managing the biodiversity impacts of other major weed species. We therefore consider the question "is the TAP a good investment in relation to protecting biodiversity?".

When a weed invasion is first discovered a decision has to be made on whether to attempt to eradicate it, contain it or do nothing. Ideally, these decisions should be based on a complete benefit-cost analysis, but this is often not possible. A partial analysis, combining knowledge of the rate of spread, seedbank longevity, costs of control and techniques of economic analysis, can assist in making a good decision. This paper presents a decision model to determine when immediate eradication of a weed should be attempted, or more generally whether weed control should be attempted at all. The technique is based on identifying two 'switching points': the invasion size at which it is no longer optimal to attempt eradication but where containment may be an option; and the invasion size at which it becomes optimal to apply no form of control at all. The model is applied to a woody perennial weed in a natural environment. The results show that seedbank longevity is the main constraint on the maximum eradicable area and spread rate is the main constraint on the maximum containment area. Stochastic simulations are undertaken to derive probability distributions of costs which are than used to evaluate the effect of budget constraints on areas that can be eradicated. We find that, in the absence of a budget constraint, it may be desirable to eradicate invasions from areas as large as 8000 ha, but when budget constraints typical of those faced by agencies in Australia are introduced, feasible eradicable areas are less than 1000 ha.

The damage that weeds inflict on natural ecosystems over time reduces the flow of services from these areas, thus reducing the flow of benefits to society. A simulation model of a natural ecosystem is a useful tool to analyse the effects of an alien plant invasion over time. Such an approach is developed here to apply the theory of production economics to value the damage through a dynamic bioeconomic model. The approach integrates the principles of benefit-cost analysis to value the costs of the incursion and the benefits of control.

Weeds have a wide variety of impacts on society, the environment and the economy. The economic impacts are usually losses and these can be measured as costs of control, decreases in yields, and reductions in economic surplus. In this paper, we attempt to estimate these economic effects of weeds in Australia. The impacts of weeds on agriculture were calculated through all three measures. But due to lack of data, the impacts of weeds on natural environments, other public land, and Indigenous land, could only be measured as the costs of control. Weeds reduce agricultural output, and so decrease farm income and increase the cost of food to consumers. The combined annual loss to farmers and consumers in 2001-02 was estimated to lie between $3442 m and $4420 m, and to average $3927 m. About 80 per cent of this annual loss falls on farmers and 20 per cent on consumers. The annual loss of $3927 m is one half of one percent of gross domestic product and 14 per cent of the value added by agriculture to the economy. These impacts in agriculture were calculated as the change in farm income and the cost of food between the current with-weeds situation and a without-weeds scenario. The difference is the maximum benefit that could be achieved by reducing the weed population, so it represents the size and national significance of the current problem. This kind of impact estimate, and information on how the loss is distributed across sectors of the economy and across industries, is a benchmark for policy and a starting point for the decision-making process. Weeds attract at least $116.4 m of government expenditure on control, surveillance and other management activities. Of this total, $19.6 m is the expenditure on natural environments by National Parks and Wildlife Services and the National Heritage Trust. Expenditure by four of the state and territory services has increased over the last four years. Of the total, $80.8 m is expenditure by other government agencies on control, inspection, research, and extension. Data on the distribution of weeds in natural environments were not available, so the value of the decrease in outputs in natural environments due to weeds could not be estimated.

Weeds have a wide variety of impacts on society, the environment and the economy. Some of the economic impacts are benefits but most are costs. Combellack (1987) valued the economic cost of weeds in 1981-82 to be $2096m. New methods of weed control and new techniques of farm management have since been developed, and new weeds have invaded. Therefore, the current cost of weed impacts cannot be readily compared to those of 1981-82. This paper attempts to estimate the economic costs of weeds in agriculture across Australia. But further, it offers an economic framework to help consider the problems that weeds create, and the generation and use of information to resolve those problems. A stochastic simulation model was developed to estimate the economic impact of weeds and to particularly account for variability in the cost estimates. The total annual economic loss to Australian agriculture ranged from $3400m to $4400m, with a mean loss of $3900m.