Accounting for spatial heterogeneity in the added conservation value of land protection when prioritizing protected areas.

To combat biodiversity loss, there is increasing interest in safeguarding habitat by expanding protected areas. Given limited resources in conservation, organizations must invest in places that will add the greatest amount of value in species protection. To determine the added conservation value of protection, one needs to consider the level of human disturbance in areas that would result if they were left unprotected. In recent years, data resources have become available that reveal the spatial heterogeneity in human disturbance over large spatial extents worldwide. We investigated how accounting for heterogeneity in future disturbance in unprotected areas affects prioritization of protected areas by determining the added value offered by protection of different areas. We applied a complementarity-based framework for protected area prioritization to select protected areas in the coterminous United States under different assumptions about the heterogeneity of future disturbance in unprotected areas. Prioritizing protected areas while incorrectly assuming spatially homogeneous disturbance in unprotected areas, a common assumption, led to a loss of 76% of possible conservation gain for a given budget. The conservation return on investment from protecting candidate areas was positively correlated (0.44) to future human disturbance in that area if it was left unprotected. Our results show that the ability to identify cost-effective protected area networks depends on how one accounts for the ecological contribution of private lands that remain unprotected.