The relative conservation impact of strategies that prioritize biodiversity representation, threats, and protection costs

Despite exponential increases in the coverage of protected areas (PAs) over recent decades, global biodiversity continues to decline. One explanation for this lack of success is that the efficacy of conservation prioritization strategies is rarely measured in terms of conservation "impact," which requires comparing proposed PA networks to a counterfactual scenario in which no intervention is applied. This approach contrasts with measuring efficacy using surrogates for conservation impact, such as the extent, total biodiversity value, or representativeness of a proposed PA network. However, implementing an experimental counterfactual scenario is difficult because of time, funding, and ethical constraints. Here, we use an alternative and complementary approach: anex-postanalysis with counterfactual outcomes measured using historical empirical data on changes in biodiversity in unprotected landscapes. This approach allows for the comparison of different retrospectively implemented prioritization strategies to a real counterfactual outcome. In our analysis, we predict the impact of several alternative PA prioritization strategies in Queensland, Australia, using high-resolution datasets of vegetation clearing, habitat type, and land acquisition cost. Our results show that achieving conventional conservation targets does not equate to achieving impact, and that alternative, and relatively simple, prioritization strategies can achieve far greater impacts.