Soil Seed Banks in Stock-piled Topsoils in the Western Rio Grande Plains, Texas

Topsoils often are removed from energy production sites and stock-piled for use later in restoration activities. Effects of this practice on soil seed banks are unknown. We examined seed bank size, species richness, and species composition of stock-piled topsoils as affected by sampling depth and sampling date at two study sites in the western Rio Grande Plains, TX, USA. Stock-piled topsoil and adjacent non-disturbed topsoil samples were collected at 0–10, 10–20, 20–30 and 30–40 cm depths on five dates over an 18-month period following stock-pile construction. Seed banks were assessed with the seedling emergence method. Sampling date had little effect on seed bank characteristics. We detected differences among depths on the stock-pile, and between stock-piles and undisturbed soil. Seed bank size and species richness generally decreased with increased stock-pile sampling depth at both sites. Differences between stock-piles and undisturbed soil varied between sites: at one site, stock-piling effects were common and were expressed in lower seed bank size and richness in stock-piles compared to undisturbed soils; at the other site, stock-piling had fewer effects on richness or seed bank size. Prevalence of exotic species varied between sites and likely reflected differences in surrounding vegetation. Therefore, site-to-site variability precludes strong generalizations. However, density of emerged native seedlings ranged from < 1 to 3.8 seedlings m−2 at both sites. Assuming acceptable species composition, stock-piles supported an adequate seed bank size at time of sampling for restoration without need for additional seed input.