Blackland Prairie Restoration in Central Texas

Abstract

The Blackland Prairie of Texas is the southernmost tip of the tallgrass prairie that spreads across the United States into Canada. Once covering over 48 million hectares in the eastcentral part of the state, Blackland Prairie has been reduced to less that 21,000 hectares in modem times, and this type of tallgrass prairie has been given a high priority for preservation and restoration. Reestablishment of Blackland Prairie is often difficult as a result of competition from exotic C4 grasses. In a randomized complete block field experiment (n=3) conducted near San Marcos, Texas, I tested the effectiveness of four levels of post-emergent herbicide, imazapic, on weed control, and establishment and growth of four native C4 grasses: Schizachyrium scoparium, Andropogon gerardii, Sorghastrum nutans, and Bouteloua curtipendula. Native grass densities, shoot growth, biomass, and percent flowering were analyzed using univarite and multivariate ANOVAs. For seedling density, all three imazapic treatments had greater seedling density than controls across species. Plants in the low imazapic treatments showed significantly greater shoot growth than those in the other two imazapic treatments and controls. End-of-season aboveground biomass for broadleaf species decreased in the imazapic treatments relative to controls, whereas biomass of the native grasses increased with imazapic treatment. Biomass of exotic grasses, however, did not differ between treatments, and despite pretreatment of the research site with Roundup® application, exotic bluestem grasses continued to dominate all treatment plots, including controls. Percent flowering of native grasses was highest in the medium imazapic treatments. Imazapic application is beneficial for native warm season grass establishment, but exotic bluestem domination prevents optimum native grass densities. Successful restoration of native grasses depends on control or elimination of exotic bluestem grasses.