Vegetation diversity and structure influence small-mammal communities in native and restored northern mixed grasslands

Current grassland restoration strategies aim to recreate grassland vegetation communities, and often rely on high-diversity native seeding to promote vegetation diversity. Questions remain concerning the influence of vegetation richness and diversity on grassland fauna. Small-mammal communities are integral parts of grassland ecosystems, but their responses to restoration are often mixed or overlooked. During July 2014 to 2016, we used Sherman live traps to survey grassland small-mammal communities of 24 study sites in northeastern South Dakota and southeastern North Dakota, USA, to better understand their responses to vegetation cover type, diversity, richness, and site-specific vegetation structure. Sites represented a vegetation species richness gradient and 3 vegetation cover types including low-diversity restorations planted with dense nesting cover (DNC) seed mix, high-diversity seeded restorations, and unseeded reference grasslands. Small-mammal abundance was highest at low-diversity DNC restoration sites and lowest in reference grassland. Small-mammal diversity was highest at high-diversity restoration sites and lowest at low-diversity DNC restoration sites. Models assessing the influence of vegetation structure on the abundance of focal taxa differed. Deer mice (Peromyscus spp.) were negatively influenced by percent native vegetation cover, and voles (Microtus spp.) showed yearly variation and were influenced positively by litter depth and negatively by vegetation richness. Small-mammal communities of low-diversity DNC restorations differed from reference sites, but high-diversity restorations were not different from reference or low-diversity DNC sites. Thirteen-lined ground squirrel (Ictidomys tridecemlineatus) abundance was higher at reference and high-diversity restored sites, while low-diversity DNC sites had higher deer mice abundance. Results indicate small mammals are unlikely to respond uniformly to vegetation characteristics, and diversity of seed mixes used in grassland restoration is likely to influence grassland small-mammal communities.