Does active plant restoration passively restore native fauna community structure and function?

Abstract

Ecological restoration commonly emphasizes reestablishing native plant communities. Implicit in this approach is the assumption that actively restoring plant communities can passively restore structure and function of other community components like wildlife. However, this assumption is rarely tested. We evaluated how plant restoration in grasslands of the northwestern United States affected the structure (composition and relative abundance) of native small mammal communities and the important functional role they play as seed predators. We quantified vegetation, small mammal community structure, small mammal seed predation, and effects of seed predation on native plant recruitment in comparable grasslands that were either native-dominated, planted with introduced forage grasses, or had undergone restoration treatments to suppress introduced grasses and increase native plants with and without supplemental watering. Native plant cover averaged ≥5 times higher at restoration sites relative to introduced grass sites. Small mammals, primarily deer mice (Peromyscus maniculatus), were least abundant in introduced grass sites and most abundant in water-supplemented restoration treatments, with intermediate levels in native and unwatered restoration sites. Seed offerings and seed sowing experiments indicated that seed predation and its effects on plant recruitment correlated with small mammal abundance, with effects generally weakest in introduced grass and strongest in restoration sites. Our results suggest that active plant restoration can passively restore the structure and function of native small mammal communities. While small mammal seed predation is a desired long-term function, it can also inhibit restoration efforts. We discuss emerging strategies for mitigating seed predation during restoration seeding.