Context. Invasive mammals have been removed from at least 100 offshore islands around New Zealand, covering a total area of around 45 000 ha.

Aims. To review the outcomes of eradications, the statutory and social environment in which the eradications were conducted, and the lessons provided for future work.

Methods. Native species to benefit from the eradications were identified, as were the reasons for the eradications and the agencies responsible. Examples are provided using case studies.

Key results. Three loosely linked work streams were revealed: research into efficient baits and baiting methods, threatened species-led projects nested within priorities for species recovery and supported by legislation, and community-led projects instigated by restoration societies. At least 180 populations of 14 species of invasive mammals were removed. Numerous species of native plants, invertebrates and more than 70 species of terrestrial vertebrates are recovering or are likely to recover as a result of the eradications. Partnerships have been formed with Māori and innovative projects developed with community groups.

Conclusions. Eradications of invasive mammals are aggressive conservation actions that can have wide benefits for biodiversity but can also be controversial, technically demanding and expensive.

Implications. Eradications are multi-scale problems. If they are to gain public acceptance, evidence is needed in support. This evidence can include understanding the detrimental effects of invasive species, the likely responses of native biodiversity, and the benefits ensuing from their recovery. However, the way this evidence is gained and communicated will also require deep understanding of nuances in regional political and cultural environments.

There are insufficient resources available globally, nationally and in many regions, to conserve all species, habitats and ecosystems. Prioritisation of targets or actions is a rational response to resource scarcity. Prioritisation can be directed at areas for reservation, species, habitats or ecosystems for management, and threat management actions. The scale at which prioritisation is applied is a fundamental decision, and the range includes global, national, regional and patch. Choice of scale influences availability of data and methods available for prioritisation. Since 1986 availability of data, computing power and expertise available have all improved globally and in many countries. Approaches to prioritisation have evolved during the past 25 years as researchers from several disciplines, including biology, ecology, decision sciences, mathematics and economics, have sought ways to achieve greater output from the resources available for biodiversity conservation. This review surveys the literature and groups prioritisation approaches into the following four categories: reserves and reserve selection, prescriptive costed biodiversity prioritisation, ranked costed biodiversity projects and contracted costed conservation actions. A concluding section considers the limitations of current prioritisation approaches and points to areas for further development.

Multiple biodiversity objectives have been proposed in conservation planning and economics for the Noah’s Ark problem – the problem of allocating limited funds to conservation projects – including species richness, persistence, taxonomic diversity, representativeness, the charismatic value of species, the broader concept of direct utility and ecological importance. However, these objectives are incommensurable and there is little consensus about which objective should be pursued, given the current state of nature. In economics, this is perhaps because the commensurability problem can be solved by converting all biodiversity objectives to monetary values. Yet, even here, a commensurability problem exists because fundamental uncertainty about species interactions means that ecological values cannot be represented in economic terms. Thus, maximising biodiversity value, combined as it is with a rational decision-making framework and assumed known probabilities of survival, can undermine the very values being pursued. This is especially the case when climate change is a current and future state of nature. Climate change adds additional complexity and fundamental uncertainties to the survival probabilities, the future value of species, the interactions among species and the probability of success of conservation projects. The associated incomplete information can lead decision makers to risky decisions under the current approach. Instead, under such conditions, the precautionary principle is appropriate. This leads to a broad conservation strategy of minimising the maximum regret and, when applied to the Noah’s Ark problem, an objective of ecosystem resilience or functional diversity rather than an objective based on economic values. The paper therefore provides an economic justification for focussing conservation resources and threatened species legislation on the resilience of ecosystems.

Context . A framework was developed to help investors improve the delivery of environmental benefits from environmental programs. The framework, Investment Framework for Environmental Resources (INFFER), assists environmental managers to design projects, select delivery mechanisms and rank competing projects on the basis of benefits and costs.

Aims . To identify design requirements for an environmental investment framework on the basis of consideration of lessons from practical experience, and established theory from decision analysis and economics.

Methods . The design and delivery of the framework are based on extensive experience from working with environmental managers and policy makers. In addition, the developers have paid close attention to the need for processes that are theoretically rigorous, resulting in a tool that allows valid comparison of projects for different asset types, of different scales and durations.

Key results . From the practical experience outlined, several important lessons and implications are identified, including the need for simplicity, training and support of users, trusting relationships with users, transparency, flexibility, compatibility with the needs and contexts of users, and supportive institutional arrangements. Use of a theoretically correct metric to rank projects can deliver dramatically improved environmental values relative to a commonly used weighted additive metric.

Conclusions . Practical and theoretical considerations have strong implications for the design of a practical, effective and accurate tool to support decision making about environmental project priorities.

Success of wildlife conservation projects is determined by a suite of biological and economic factors. Donor and public understanding of the economic factors is becoming increasingly central to the longevity of funding for conservation efforts. Unlike typical economic evaluation, many costs and benefits related to conservation efforts are realised in non-monetary terms. We identify the types of benefits and costs that arise from conservation projects and examine several well developed techniques that economists use to convert benefits and costs into monetary values so they may be compared in a common metric. Costs are typically more readily identifiable than benefits, with financial project costs reported most frequently, and opportunity and damage costs reported much less often. Most current evaluation methods rely primarily on cost-effectiveness analysis rather than cost–benefit analysis, a result of the difficultly in measuring benefits. We highlight improved methodology to measure secondary costs and benefits on a broader spatial scale, thereby promoting project efficacy and long-term success. Estimation of the secondary effects can provide a means to engage a wider audience in discussions of wildlife conservation by illuminating the relevant impacts to income and employment in local economies.

Context.Comprehensive evaluation of biodiversity conservation programs is essential for informing their development as well as the design of future programs. Such evaluations should not be limited to whether targets have been met, but should also assess the cost and efficiency of meeting targets, and any factors contributing to success or failure.

Aims.We aimed to evaluate the effectiveness and efficiency of individual-species conservation programs, and the biological and operational factors affecting these. We used the species action plans (SAPs) within the UK Biodiversity Action Plan as our case study.

Methods.We used cost–effectiveness analysis, cost–utility analysis and threat-reduction assessment to evaluate the effectiveness and efficiency of individual SAPs. Then we used statistical models to investigate the relative importance of biological and operational factors affecting cost, effectiveness and efficiency.

Key results.Conservation plan success was affected by both biological and operational factors. Invertebrate plans tended to be less effective, whereas vertebrate plans were less efficient. Plans for widely distributed species with longer generation times tended to be less efficient. Of the three different evaluation approaches, cost-effectiveness analysis offered the best combination of ease of data collection and accuracy of data content.

Conclusions.The most successful SAPs concerned species with short generation times and narrow distributions. Operationally, the most successful SAPs were concise and focussed and showed clear lines of responsibility for implementation.

Implications.Techniques such as cost–effectiveness analysis, cost-utility analysis and threat reduction assessment should be used to inform decisions on maximising the rate of return on conservation investments, although broader ecological implications and socio-cultural benefits should also be considered. The success of conservation plans is influenced by both biological and operational factors. Because biological factors cannot be controlled or altered, where species exhibit characteristics that are likely to make their conservation less effective or efficient, it is critical that operational factors are optimised. High-quality data are necessary to underpin prioritisation decisions, and monitoring to deliver reliable data on both the benefits and costs of conservation should form a core component of conservation programs.

Context. Impact avoidance and biodiversity offsetting are measures that can be used for alleviating environmental impacts of economic development projects. Offsetting is frequently implemented via habitat restoration. Biodiversity offsets should be designed in a cost-effective manner.

Aims. To investigate how spatial conservation prioritisation methods, most commonly used for reserve network design, could be used for informing impact avoidance and biodiversity offsetting.

Methods. Zonation is a publicly available framework and software for grid-based, large-scale, high-resolution spatial conservation prioritisation. Zonation produces a hierarchical, balanced, and complementarity-based priority ranking through the landscape, identifying areas of both highest and lowest conservation value in one analysis. It is shown how these capabilities can be utilised in the context of impact avoidance and offsetting.

Key results. Impact avoidance can be implemented by focusing environmentally harmful activity into low-priority areas of the spatial priority ranking. Offsets can be implemented via a more complicated analysis setup. First, identify development areas unavailable for conservation, which leads to a decrease in the quality of conservation value achievable in the landscape. Second, develop compensation layers that describe the difference made by allocation of extra conservation action. Running a spatial prioritisation, integrating information about where species are (representation), what areas and features are damaged (reduced condition and negative connectivity effects), and the difference made by remedial action, allows identification of areas where extra conservation effort maximally compensates for damage. Factors such as connectivity and costs can be included in this analysis. Impact avoidance and offsetting can also be combined in the procedure.

Conclusions. Spatial conservation-prioritisation methods can inform both impact avoidance and offsetting design.

Implications. Decision support tools that are commonly associated with reserve selection can be used for planning of impact avoidance and offsetting, conditional on the availability of high-quality data about the distributions of biodiversity features (e.g. species, habitat type, ecosystem services).

A range of methodological frameworks is available to assist decision-makers with evaluations of projects concerned with biodiversity conservation (the protection, management or restoration of biodiversity), but their uptake has been relatively limited. Some researchers suggest a lack of research interest to be one contributory factor, in particular in relation to the application of interdisciplinary approaches that integrate methods from the natural and social sciences, despite the insights that such approaches can bring. We evaluated this assertion by examining the provenance of some examples of current research in this area. Specifically, we compared two exemplar papers published in a conservation journal and one in an interdisciplinary ecological economics journal. We scored the cited references in each paper according to standard subject categories. These scores were then weighted and aggregated to give an overall quantified subject category distribution for each of the three focal papers. Comparison of the three papers revealed an expected dominance of subject categories most closely aligned with ecological science. However, there were different patterns of provenance in the three papers. One paper from the conservation journal was dominated by citations of other papers in the biodiversity conservation literature. The second paper from the conservation journal and the paper from the ecological economics journal displayed similar overall patterns of disciplinary provenance, although they diverged in disciplinary provenance for the less commonly cited disciplines, such as the social sciences. Our results suggest that research in biodiversity project evaluation may be developing along at least three, relatively distinct, pathways rather than as a genuinely interconnected research theme. This is likely to hinder progress in research but also in practical application of the techniques, in terms of reducing the likelihood of identifying inadequate, inappropriate or inefficient conservation investments. There is still considerable opportunity for further collaboration in the areas of biodiversity evaluation among researchers in a range of disciplines, including ecology, economics, statistics, forestry and wildlife management. Biodiversity conservation evaluation is a growing field, but its potential is unlikely to be fulfilled unless biodiversity researchers seek to develop a more integrated community, and particularly, to learn from researchers in other disciplines where evaluation has a longer history.