Effects of planned grazing and burning to restore tallgrass species in old-field sites under drought conditions in Texas Blackland Prairie

摘要

We examined if reintroduction of grazing with or without burning would enhance succession towards native prairie vegetation on previously over-seeded old-field tallgrass prairie subjected to mowing or burning. We hypothesized that returning grazing and fire to these seeded and old-field sites would change establishment and competitive relationships among plant species to benefit fire-tolerant prairie species. Grazing and burning had neutral effects on native prairie species on the previously seeded and unseeded sites over a study period that experienced 70 % of normal precipitation. Herbaceous group categories included old-field grasses, seeded tallgrasses, other grasses (< 2%), seeded perennial forbs, other perennial forbs, and annual forbs. Seeded species comprised about 70 % of the community on seeded plots and 10 % on unseeded plots for the eight years of this study. Seeded-ungrazed tallgrass biomass increased 19 % and on seeded-unburned sites biomass increased 11 %. Tallgrass biomass of unseeded-grazed burned treatment remained at about 4% throughout the study, but with no grazing or no burning biomass, doubled. Changes in biomass associated with treatments led to changes in soil temperatures near the soil surface in summer months. Community dissimilarity was most affected by seeding followed by year, grazing, and burning (P's = 0.001). Collectively, seeded or unseeded, grazed, or ungrazed site soil temperatures averaged 4.8 degrees C higher than tree-shaded sites in afternoons of hotter months. Soil temperature differences were inversely proportional to successful site restoration. During afternoons of hotter months, soil temperatures of seeded sites were 1.1 degrees C lower than unseeded sites, while grazed sites were 2.0 degrees C greater than ungrazed sites, and burned sites were 1.6 degrees C higher the year of the burn than unburned sites (P's < 0.05). While grazing and burning had neutral effects on previously seeded and unseeded prairie sites, seeding accounted for about 70 % of the community on seeded plots and 10 % on unseeded plots.