Unusually high-quality soil seed banks in a Midwestern US oak savanna region: variation with land use history, habitat restoration, and soil properties

An overarching conclusion in the literature is that soil seed banks rarely contain many restoration-target species and are often liabilities rather than assets to restoration. Our objective was to evaluate composition and spatial variation of seed banks and their potential contributions to restoration, including restoration-target species such as rare species and those characterizing historical habitats. On 64 sites in a Midwestern U.S. oak savanna landscape, we sampled soil seed banks in seven habitat types (restored oak savannas, oak woodlands, and mesic prairies; unmanaged upland oak and mesic forests; and unmanaged and managed pine plantations). The germinable seed bank was exceptionally rich in restoration-target species. In total for the 64 sites, seedlings of 127 species emerged from seed bank samples. Of the 101 native species, 56 were restoration-target species, an unusually high number among seed bank studies. Restoration-target species in seed banks included 13 threatened or endangered species, in addition to 43 other specialist species associated with high-quality native habitats or on a floral list thought to characterize historical ecosystems. When analyzed across the 64-site gradient, seed banks differed among the seven habitat types and varied with historical (1939) land use, recent management activities that restored open-structured habitats, and biophysical gradients of tree density, soil drainage, and soil texture. While not all restoration-target species were detected in the seed bank, the unusually high-quality seed bank is a potential asset to restoration and was partly structured along environmental gradients across the landscape.