Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture

Department

Plant and Soil Science

First Advisor

Dr. Thomas G. Barnes

Second Advisor

Dr. William W. Witt

Abstract

Despite the agronomic benefits of exotic grass plantings for pasture and rangeland forage, exotic grass invasions are capable of having dramatic and widespread impacts on native communities and ecosystems. Exotic Old World bluestem grasses (OWBG; Bothriochloa and Dichanthium spp.) have become increasingly invasive throughout the central and southern U.S. Little is known regarding the impacts of OWBG invasion on native grassland and savannah ecology and how to successfully control OWBG invasions in natural areas. Accordingly, this dissertation research had several objectives: 1) Evaluate the efficacy of herbicide and/or disking to control OWBG; 2) Assess the relative competitive ability of the OWBG, Kleberg bluestem (Dichanthium annulatum); 3) Evaluate herbicide application and native grass seeding to rehabilitate an OWBG invaded coastal prairie; 4) Examine whether ecosystem function differs between areas dominated by OWBG vs. native coastal prairie; and 5) Characterize the germinable soil seed bank of an OWBG invaded coastal prairie.

Herbicide treatments of imazapyr, glyphosate, and imazapyr + glyphosate were found to provide effective, albeit temporary, OWBG control (often less than six months). A combination regimen of disking followed by herbicide treatments, regardless of herbicide active ingredient or application rate, controlled OWBG more effectively than herbicide alone or herbicide followed by disking. Herbicide treatments followed by native grass seeding did not markedly rehabilitate coastal prairie invaded by OWBG. OWBG appeared to reinvade from the seed and/or bud bank suggesting the restoration of OWBG invaded grasslands will likely require aggressive and repetitive control methods to completely extirpate OWBG at a given site before native plantings occur. A seed bank survey revealed the density of OWBG germinable seeds increases dramatically with increasing OWBG invasion (i.e., canopy cover) while the native grass seed bank is generally depauperate even when levels of OWBG invasion were low.

Dominance of OWBG appears to have altered native coastal prairie ecosystem function; yet the directionality and extent of OWBG effects were strongly soil texture dependent. Here, ecosystem function parameters between areas dominated by OWBG compared to native prairie differed most often on sandy loam vs. clay soil. Moreover, DeWit replacement series experiments revealed the relative competitive ability of Dichanthium annulatum was significantly greater than the native grass, little bluestem (Schizachyrium scoparium).

OWBG will likely persist throughout the central and southern Great Plains, USA, for years to come and intensive management efforts will be necessary to keep OWBG invasions under control in natural areas of high conservation value.

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