Wetland landscape transformation by beavers: responses of biodiversity and functional indicators at multiple scales

Abstract Context Landscape-scale restoration is needed to reverse declines in biodiversity, but the ecological processes that sustain biodiversity by boosting heterogeneity are often overlooked. Large herbivores are important drivers of heterogeneity and are increasingly being used to restore lost dynamic processes. Objectives With beaver populations recovering from a historic low, we test what their ecosystem engineering potential means for biodiversity and ecosystem functioning at multiple scales. Methods We quantified 10 taxonomic groups at sample, site and landscape scale via in-situ surveys (plants and water beetles) and eDNA sampling (invertebrate and vertebrates) from nine beaver-created wetlands and nine wetlands unmodified by beavers (control wetlands) in Evo, Finland. Results Per taxonomic group, the mean and total number of taxa at sample and site-scale was mostly similar between wetland types, though significantly higher in beaver wetlands at sample (true flies) and site-scale (plants and true flies). 63% of all taxa were shared by beaver-created and control wetlands. However, both wetland types supported unique taxa with beaver wetlands increasing the landscape taxon pool by an average of 19% (range 0–40%), most notably for plants, beetles, true flies and may/stone/caddisflies. Plant functional diversity was 55% higher in beaver compared to control wetlands. Conclusions Beaver wetlands are integral to reinstating dynamic ecological processes that provide refugia for multiple taxonomic groups, supporting taxa otherwise absent from the landscape. Our findings hint at the scale of past biodiversity loss associated with beaver-dependent wetlands, while offering a glimpse of what could be gained from their ongoing population recovery.