Seed limitation may prevent successful restoration of native plant communities. Seed addition is a common restoration practice but the role of small mammals in affecting seedling recruitment is not well understood. The purpose of this investigation was to test the relative effect of seed introduction in combination with small mammal and bird exclosures in an Ohio wet meadow. We ask whether the ambient population of Microtus pennsylvanicus (1) alters species composition (e.g. forb/grass/sedge, invasive, non-native); (2) influences plant diversity; and (3) reduces the effect of increasing local plant richness through seed introductions. We established a 2×2 factorial design including a seed addition treatment (0 and 20 seed species added) and an exclosure treatment (open and fenced to exclude all mammalian and bird herbivores and granivores). Seeds from twenty native species were selected to represent a broad range of plant life forms typically found in temperate eastern North American wet meadow communities. All species were obligate or facultative wetland species with forbs, grasses and sedges represented. We found that forb species increased inside exclosures, especially in the seed addition treatment. We also found that relative biomass of invasive species was reduced in exclosures and with seed addition. Species richness increased with seed addition; however, exclosures significantly increased species richness and diversity, particularly of those species that were experimentally introduced by seed. Our results support the seed limitation hypotheses. It is also evident that seed and seedling predation are important factors that can control wet meadow community composition and diversity.