North American grasslands and grassland birds have declined drastically due to habitat degradation by fire suppression (i.e., woody encroachment), fragmentation, and conversion to croplands. A better understanding is needed of the relationships among disturbance regimes (e.g., fire), resultant vegetation changes, and grassland bird communities to effectively manage remaining grasslands and grassland birds. I assessed the relationship between post-fire succession, and mean relative abundance and nesting ecology of breeding grassland birds (i.e., nest-site selection and nest success) in mesquite-dominated rangeland of the Texas Rolling Plains, where prescribed fire is used as a tool to manage shrub encroachment. Brush cover, grass cover, and visual obstruction generally increased with post-fire succession, and bare ground decreased with post-fire succession. Species richness, grasshopper sparrows (Ammodramus savannarum), Cassin’s sparrows (Aimophila cassinii), and dickcissels (Spiza americana) responded positively to post-fire succession, and lark sparrows (Chondestes grammacus) responded negatively to post-fire succession.; abundance of these avian groups was low on the control sites. During 2004–2005, 90 grassland bird nests were monitored. I found conflicting results for vegetation parameters important to nest site selection and probability of nest success. For all species except lark sparrows, nest-site location was positively associated with visual obstruction and with grass or forb cover. However, the probability of nest success increased with lower visual obstruction, bare ground cover, or grass cover. Grassland bird abundance, nest-site location, and nest success had differing associations with vegetation variables. These results suggest that to effectively manage remaining grasslands for sustainable breeding grassland bird populations, managers should engage in practices that keep habitat in multiple vegetative successional stages.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Ecology and Evolution." Includes bibliographical references.

Thesis (Ph. D.)--University of Kentucky, 2005. / Includes bibliographical references (p. 203-220). Also available in PDF format via the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The objectives of the study were to provide a documented record of the vegetation of the grassland vegetation of the Red River Valley. The native prairies of this Valley are dominated by various combinations of Andropogon gerardi, Andropogon scoparius, Agropyron smithii, Bouteloua curtipendula, Calamagrostis inexpansa, Calamovilfa longifolia, Koeleria cristata, Muhlenbergia richardsonis, Sorghastrum nutans, Spartina pectinata, Sporobolus heterolepis, Stipa comata, Stipa spartea and Stipa viridula. At present only relicts of these grasslands remain. One hundred and fifty-one stands including 299 species, encompassing a wide range of floristic and habitat variability, were selected for study. The species composition frequency) of each stand was sampled by the use of thirty 0.5 X 0.5 m quadrats. A presence list was prepared for each stand and the dominant graminoid species determined by an estimate of cover contribution to the upper strata. The standing crop of green herbage of .34 stands was sampled by clipping five 0.5 X 0.5 m quadrats, and the material oven dried for weight determination. Environmental measurements were taken to determine physiographic position and soil profile characteristics. Soil samples were collected from the "A" horizon of each stand for textural analysis, field capacity, salinity and pH determinations. An analysis based on indicator species determined by physiographic association, indicated that the various species responded in a continuous manner to a moisture gradient. This was suggested by a gradation of importance from one physiographic habitat to another, with its position of peak performance in association with a specific drainage position. Vegetational types were also associated with physiographic position, but the dominant species and to a lesser degree secondary species showed modification of behavior by soil texture. The total number of species and their levels of importance (frequency) within the various vegetational types was used as a measure of diversity. The mid prairie dominance types with high numbers of species, many with high importance, were the most diverse of all types examined. It was further indicated that mid prairie stands in the northern portion of the area studied had higher diversity than all others. Geographic differences in diversity were related to historical development of the grasslands. The yield of green herbage varied according to prairie division, leading dominant, soil texture and geographic location. A high positive correlation between green herbage yield and length of growing season suggested that geographic location was the most effective determinant in production, with southern stands producing about 100% more green herbage than comparable stands in the north. The species comprising the grasslands of the Red River Valley suggest an amalgamation of species of eastern and western origin. The dominant graminoids, however, are most closely associated with the grasslands to the east and suggest the placement of the Red River Valley grasslands within the True Prairie.

No description available.

No description available.

Fluxes of sensible and latent heat were measured over a grassland during 1998 and 1999 using the eddy covariance technique. The study objectives were to document seasonal and interannual variation evapotranspiration. Bowen ratios were lower in 1998 (0.5-3.0) than in 1999 (2.5-8.5) due to lower evapotranspiration rates (E). Maximum E also occurred later in 1998 than in 1999; Day 188 (10.4 mmol m-2s-1) versus Day 152 (5.6 mmol m-2s-1). Daily evapotranspiration rates were positively correlated with net radiation, canopy conductance, plant nitrogen content, leaf area index and soil moisture. Based on calculations of the decoupling coefficient (O). evapotranspiration was more constrained by canopy conductance in 1999 (O<0.2) than in 1998 (O>0.3). Evapotranspiration and energy partitioning in this grassland were sensitive to seasonal changes in soil moisture and interannaual variation in spring precipitation. Annual evapotranspiration was 300 mm. / x, 70 leaves : ill. ; 28 cm.

The mixed-grass prairie region of southwestern Manitoba is a hotspot for many endangered grassland birds. This region has been degraded to less than a quarter of its historical amount of mixed-grass prairie. Remaining prairie is primarily used for livestock grazing. The objective of this study was to evaluate the contribution of sustainable land management practices, such as rotational grazing, in the conservation of this region. In 2008 and 2009, I compared the abundances of grassland birds on two grazing regimes, twice-over rotation and season-long, to ungrazed fields. Bird surveys were done during the breeding season and were conducted using 100-m fixed-radius point-count plots. I determined the effects of treatment, landscape and vegetation characteristics on songbird abundances using generalized linear mixed models. Grassland birds selected grazed pastures over ungrazed fields in both years, and species richness of obligate grassland birds was significantly greater (α = 0.10) on season-long than twice-over pastures (β = 0.419, p = 0.032, in 2008 and β = 0.502, p = 0.043 in 2009). Season-long grazing may actually benefit grassland bird communities by creating somewhat temporally stable areas of high use and low use within the pasture. However, nesting success studies and long-term monitoring are necessary to further understand how twice-over rotation grazing systems contribute to the conservation of grassland birds in southwestern Manitoba.