<p> Overall, the results of this study show that there are evident trends among the three ecoregions and delta of the White River. The forest stands of the Pine Ridge/Pierre Shale Ecoregion are the oldest along the river, as evidenced by aerial mapping going back into the 1930s and by the larger average trunk diameters of the trees. Historic aerial photographs for this ecoregion shows a relative static system from the 1930s-2010, with little destruction of existing or creation of new forests within the floodplain. Along with the older age of the forests, the stands in this ecoregion have the lowest floral diversity. The Pine Ridge/Pierre Shale forests are also unique along the river in that they are largely dominated by Acer negundo (box elder), a late-successional species that is largely absent from the forests of the other ecoregions. As the river continues downstream and enters the Badlands Ecoregion it gains size and volume, while its riparian forests decrease in patch size and tree density. Although the forests become smaller, the variety of communities and diversity of species increase. Unlike the Pine Ridge/Pierre Shale Ecoregion, the Badlands&rsquo; land cover was dynamic from the 1930s-2010, with increases in forest and declines in river channel area (-29%). Farther downstream and with a larger river channel, the River Breaks has even larger and more diverse riparian forests and the highest plant species richness and diversity among the ecoregions. The rate of land cover change was the greatest in the River Breaks, as the larger river has greater power for eroding existing communities and depositing sediment for recruitment. The area of riparian woody vegetation increased sharply from the 1930s-2010 (58%), while the area of channel declined (-20%). This ecoregion had the most perennial streamflow, with fewer zero flow days than in the upstream ecoregions. The Delta is unique as the only portion of the river where flows are affected by the Fort Randall Dam on the Missouri River. The impact of the reservoir on the area is evident, as it has the largest proportional area of forest along the river, as well as having the flora with the highest wetland affinity.</p>

<p> Increased nutrient availability has been widely linked to the success of invasive plants, however a general mechanism explaining these observations is lacking. Stoichiometric homeostasis (<i>H</i>), which is the regulation of internal nutrient concentrations, has been used to explain changes in plant community diversity under alterations in nutrient availability. One hypothesis holds that plants with high regulation (larger <i>H</i>) decrease in abundance in nutrient enriched conditions but are stable in nutrient deficient and drought conditions, likely due to extensive root systems. Additionally, plants with low regulation (lower <i>H</i>) increase in abundance under nutrient enriched conditions but are sensitive to drought conditions. I tested the hypotheses that <i>H</i> would be higher in native grasses than in invasive grasses, that <i>H</i> would be modulated by environmental conditions, and that differences in <i>H</i> would be associated with differences in growth and biomass allocation. I calculated <i> H</i> and measured plant growth and growth traits in two native (<i> Pascopyrum smithii</i> and <i>Elymus canadensis</i>) and two invasive (<i>Bromus inermis</i> and <i>Agropyron cristatum </i>) grasses grown in two experiments. Both experiments contained a range of N:P fertilizer supply concentrations and the first experiment contained a two-level drought treatment while the second experiment contained a two-level mycorrhizal inoculation treatment. </p><p> In the first experiment, I found support for the hypothesis that <i> H</i> is higher in native than invasive plants, that environmental conditions (i.e. water availability) affect the value of <i>H</i>, and that differences in <i>H</i> were associated with differences in growth. In the second experiment, there was no successful mycorrhizal inoculation, resulting in no differences in <i>H</i> between mycorrhizal treatment groups. There were significant differences in total growth between the second experiment native and invasive grasses, despite there being no significant differences in <i>H</i>. Differences in <i>H</i> values between control-treated grasses in the two experiments may be due to differences in greenhouse temperature and light conditions. These results show first, significant differences exist in <i>H</i> between invasive and native grasses, with invasive grasses expressing lower values of <i> H</i>, second, environmental conditions effect the expression of <i> H</i>, and third, that differences in the expression of <i>H</i> are matched by differences in growth.</p><p>

Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2009. / Title from PDF t.p. (viewed on Feb. 5, 2010). Source: Dissertation Abstracts International, Volume: 70-04, Section: B, page: 2009. Adviser: Loren H. Rieseberg.