Is conservation right to go big? Protected area size and conservation return-on-investment

Policy guidelines for creating new protected areas commonly recommend larger protected areas be favored. We examine whether these recommendations are justified, providing the first evaluation of this question to use return-on-investment (ROI) methods that account for how protected area size influences multiple ecological benefits and the economic costs of protection. We examine areas acquired to protect forested ecosystems in the eastern US that are rich in endemic species. ROI analyses often alter recommendations about protected area size from those obtained when considering only ecological benefits or only economic costs. Large protected areas offer a greater ecological return per dollar invested if the goal of protecting sites is to reduce forest fragmentation on the wider landscape, whereas smaller sites offer a higher ROI when prioritizing sites offering protection to more species. A portfolio of site sizes may need to be included in protected area networks when multiple objectives motivate conservation.