Environmental <scp>DNA</scp> quantifies the terrestrial biodiversity co‐benefit of forested riparian buffers in agricultural landscapes

Abstract The conversion of natural ecosystems to agriculture is a leading cause of habitat loss and threatens global biodiversity. For the past two centuries, the Midwestern United States has experienced agricultural intensification and expansion, resulting in losses of natural ecosystems like forests. Forest cover in states like Illinois has increased over the last several decades, partially due to agricultural conservation practices like riparian buffers. However, does this increasing forest cover, intended to reduce nutrient and soil loss and benefit in‐stream biota, also benefit terrestrial biodiversity? To evaluate how forest cover influences and potentially benefits terrestrial vertebrates in agricultural landscapes, we collected environmental DNA (eDNA) samples from 47 low‐order streams over a riparian forest cover gradient and conducted eDNA metabarcoding of vertebrate communities using 12S and COI primers. Sites with complete (100%) riparian buffers supported three times the terrestrial vertebrate taxa richness compared to sites lacking buffers entirely (0%). Increased vertebrate taxa richness at highly forested sites was driven by the turnover of communities to forest‐associated species like southern two‐lined salamander ( Eurycea cirrigera ) and red‐eyed vireo ( Vireo olivaceus ), whereas unforested sites were dominated by common rodent taxa. Synthesis and applications. We demonstrate that eDNA metabarcoding has the potential to rapidly quantify the benefits of agricultural conservation to terrestrial wildlife across taxa. Notably, we found that riparian buffers along streams in the Midwestern United States return an increase of one taxon for every 10% increase in forest cover, an important potential benefit of this conservation action in an intensive agricultural landscape.