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The Blackland Prairie of east-central Texas, the southernmost tip of the once vast North American Tallgrass Prairie, now covers only 1% of its original 6.8 million hectares. Thus, there is considerable interest in restoration and re-establishment of this endangered ecosystem. In a randomized complete block field experiment conducted near San Marcos, Texas, we tested the effectiveness of the post-emergent herbicide imazapic on weed control, establishment, and growth of four C4 warm-season grasses native to the Blackland Prairie (Andropogon gerardii, Sorghast rum nutans, Schizachyrium sco- parium, and Bouteloua curtipendula). Treatment with three different levels of imazapic (0.07, 0.092, and 0.138 kg ai/ha) all significantly increased seedling density of native grasses, and low-to-medium levels of imazapic increased seedling shoot growth and flowering relative to water controls. End-of-season aboveground biomass of native grasses also increased with imazapic treatment while that of broadleaf species decreased. However, shootbiomass of exotic C4 grasses (principally Bothriochloa ischaemum and Dichanthium sericeum), the dominant species of this site prior to study, was not significantly affected by imazapic treatment. Despite vigorous site preparation and pretreatment with a broad-spectrum herbicide (Roundup®), these exotic C4 bluestem grasses continued to dominate all treatment plots. These findings indicate that while imazapic is beneficial for native warm season grass establishment, it is inadequate to effectively control these exotic bluestems, which are abundant on many sites once occupied by Blackland Prairie. Successful restoration of native grasses in the Blackland Prairie will, therefore, require more effective means of controlling or eliminating these aggressive exotic species. [ABSTRACT FROM AUTHOR]

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% of seedlings). 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. [ABSTRACT FROM AUTHOR]

Examines the composition of understory wood vegetation in Plateau live oak clusters in relation to cardinal direction at upland savannas of the Edwards Plateau in central Texas. Discussion on spatial asymmetry in the woody plant community; Species composition of the woody understory community; Implications for the study of mechanism of facilitation in woody clusters.