Systematic conservation planning (SCP) is a rapidly advancing discipline aimed at providing decision support for choices between alternate conservation actions. SCP is often used to inform choices about areas to protect, in order to optimize outcomes for biodiversity while minimizing societal costs. Despite the widespread application of SCP approaches, there is limited understanding of the types of impacts resulting from related projects, and when and where it is most effective. This is compounded by the absence of a standardized approach to evaluating and reporting on the outcomes of SCP projects. We highlight the challenges of undertaking evaluations of complex planning processes, the current state of knowledge about the outcomes of SCP projects, and emerging opportunities to improve evaluation. There is a need for clarity around theories of change, definitions of SCP and impact, and standardized reporting and information sharing across the discipline.

Emerging policies worldwide require biodiversity gains as compensation for losses associated with economic development, seeking to achieve "no net loss" (NNL). Multipliers -factors by which gains are larger than associated lossescan be crucial for true NNL. Here, we review the theoretical literature on multipliers. Then, we collate data on multipliers implemented in practice, representing the most complete such assessment to date. Finally, we explore remaining design gaps relating to social, ethical, and governance considerations. Multiplier values should theoretically be tens or hundreds when considering, for example, ecological uncertainties. We propose even larger multipliers required to satisfy previously ignored considerations -including prospect theory, taboo trades, and power relationships. Conversely, our data analyses show that multipliers are smaller in practice, regularly <10.0, and have not changed significantly in magnitude over time. We recommend that NNL policymakers provide explicit multiplier guidelines, require larger multipliers where appropriate, and ensure transparent reporting of multipliers used. Further research is necessary to determine reasons for the implementation gap we have identified. At the same time, there is a need to explore when and where the social, ethical, and governance requirements for NNL reviewed here can be met through approaches other than multipliers.

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