Melissa Chapman, Carl Boettiger, Justin S Brashares

Coincident with international movements to protect 30% of land and sea over the next decade (‘30x30’), the United States has committed to more than doubling its current protected land area by 2030. While publicly owned and managed protected areas have been the cornerstone of area-based conservation over the past century, such lands are costly to establish and have limited capacity to protect areas of highest value for biodiversity conservation and climate change mitigation. Here we examine the current and potential contributions of private land for reaching 30x30 conservation targets at both federal and state scales in the U.S. We find that compared to protected public lands, protected private lands are more often in areas designated as high conservation priority, hold significantly higher mean species richness, and sequester more vulnerable land-based carbon per unit area. These and related findings highlight the necessity of mechanisms that engage private landholders in enduring conservation partnerships.