WOODY PLANT EFFECTS ON SOIL SEED BANKS IN A CENTRAL TEXAS SAVANNA

We studied germinable seed banks in soil associated with grasslands, relatively young (<40 years) juniperus ashei (Ashe juniper), and long-established Quercus virginiana var. fusiformis (plateau live oak) patches of woody plants in a central-Texas savanna to ascertain the degree to which Ashe juniper alters the seed bank of sites previously inhabited by grassland vegetation, and to assess how seed banks differ beneath two common types of patches associated with woody plants in this savanna ecosystem. Across all habitats and over an annual growth cycle, 3,364 seedlings representing 116 species emerged from these seed banks. Annual forbs were the dominant life form in all habitats (62% ofseedlings). The fraction of perennial forb and graminoid seedlings was comparable (19 versus 18%, respectively), and seedlings of woody plants were rare. Density, diversity, and species composition of seed banks varied significantly among the three habitats. Seed banks in grassland and live oak were most dissimilar, and seed banks of Ashe juniper were intermediate in species composition. Early-to-mid-successional species present in grasslands were absent from seed banks of Ashe juniper. Late-successional species of grasses were either absent or few in the seed bank in all habitats. Results indicate that occupation of grasslands by Ashe juniper alters seed banks after a relatively short time, and these changes are distinct from patches of woody plants that have a long-term history of occupation of sites. Approaches to restoration of grasslands that involve removal of Ashe juniper alone cannot rely on the soil seed bank for rapid reestablishment of climax grassland communities.