Protected areas (PAs) are an indispensable and generally effective policy for protecting biodiversity in the Anthropocene. However, this is dependent on whether PAs are sited in the “correct” locations. There are multiple ways of defining “correctness”, and this is often context-, taxa-, and stakeholder-specific. For example, total biodiversity coverage, threatened/endemic biodiversity coverage, and current/future value of habitat are all possible metrics with which we can quantify the potential biodiversity benefit of land protection. However, we argue that incorporating additionality (i.e., whether land protection merely protected land that was not going to be developed anyway, in which case there is no additionality) and cost-effectiveness (i.e., are we getting good value for our investment in land protection)―two factors rarely included in large-scale assessments of PA efficacy―will provide fresh perspectives to understand how effective expansion of the PA network has been. Here, we analyze the expansion of the PA network in the conterminous US since 1970 to examine how coverage of all as well as small-ranged/threatened terrestrial birds, mammals, and amphibians has changed. We integrate past and present land-cover/use maps and parcel-level property value data to assess the efficacy of PA network expansion that incorporates additionality and cost-effectiveness and investigate their spatial concordance.
Results/Conclusions
The PA network in the conterminous US has expanded steadily since 1970. However, new PAs were not always sited in regions of high total or endemic/threatened species richness. Our analyses reveal hotspots of total and endemic species richness that require urgent protection. We also find that PAs are increasingly sited in “high-and-far” locations, consistent with global patterns. Incorporating past and present land-cover/use data and land-use change modeling into our analyses, we find that there is limited additionality in PAs sited since the 1970. PAs were mostly sited in areas that were not projected to undergo land-use change even in the absence of PAs. Accounting for spatial variation in land costs, PAs sited since the 70s were not significantly more cost-effective than randomly protected parcels. Last, we show that the conservation efficacy of recent PAs at the county-level is shaped by a complex interplay of physical environment (e.g, elevation; land-cover/use), socio-economic (e.g., land-cost), and human demographic variables (e.g., population; income). By providing novel perspectives in quantifying conservation efficacy of PAs sited since 1970, our findings can inform how we can better place future protected areas in “correct” locations to meet one or more conservation objectives/criteria.