Abstract - Impacts of Annual Brome Grasses, Bromus japonicus and Bromus tectorum, on the Structure and Function of a Mixed Grass Prairie Ecosystem
Ogle, Stephen M. 2000. Impacts of Annual Brome Grasses, Bromus japonicus and Bromus Tectorum, on the Structure and Function of a Mixed Grass Prairie Ecosystem. 135 p.
The annual brome grasses, Bromus japonicus and Bromus tectorum, are common invaders of grasslands in the Northern Great Plains. This research evaluated the ecosystem impact of the annual bromes on a mixed grass prairie at Wind Cave National Park, South Dakota. The study had three primary objectives.
The first objective was to determine the vegetation that was most commonly invaded by the bromes. This was done by sampling at two scales. A coarse-scale approach entailed sampling across 3824 ha. Results showed that annual bromes were most common on transects with grassland vegetation dominated by C3 grasses, particularly Agropyron smithii and Stipa viridula, and in shrubland vegetation dominated by Symphoricarpos occidentalis. A fine-scale approach entailed sampling two, one ha sites. Results showed that annual bromes were negatively associated with Poa pratensis, presumably due to a competitive interaction exaggerated by their common phenology.
The second objective was to investigate annual brome impacts on ecosystem structure and function, including plant biomass, root shoot rations, litter accumulation, soil moisture, soil temperatures, soil organic matter, nitrogen mineralization, and aboveground litter decomposition. The impacts were investigated using three approaches: 1) evaluating variability in properties across natural gradients of brome abundance, 2) comparing differences between the extreme high and low brome plots on the gradient, and 3) estimating effects following brome removal in a paired plot experiment. The first two approaches showed that bromes had the greatest impact by decreasing plant biomass and increasing aboveground litter pools; the paired plot experiment corroborated these impacts. Collectively, findings supported the view that annual bromes are an important plant functional type in a mixed grass prairie.
The third objective was to investigate the potential long-term impact of the annual bromes on soil organic carbon using the CENTURY simulation model. Model results showed that bromes affect the storage of organic carbon in the soil by having a high root turnover, greater transpiration in the spring, and roots with high lignin content, compared with perennial grasses. The brome impact with concomitant climate change reduced soil organic carbon, particularly with more extreme climatic warming and greater increases in precipitation.
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