Matching Items (2)
Description
Climate change has the potential to affect vegetation via changes in temperature and precipitation. In the semi-arid southwestern United States, heightened temperatures will likely lead to accelerated groundwater pumping to meet human needs, and altered storm patterns may lead to changes in flood regimes. All of these hydrologic changes have the potential to alter riparian vegetation. This research, consisting of two papers, examines relationships between hydrology and riparian vegetation along the Verde River in central Arizona, from applied and theoretical perspectives. One paper investigates how dominance of tree and shrub species and cover of certain functional groups change along hydrologic gradients. The other paper uses the Verde River flora along with that river's flood and moisture gradients to answer the question of whether functional groups can be defined universally. Drying of the Verde River would lead to a shift from cottonwood-willow streamside forest to more drought adapted desert willow or saltcedar, a decline in streamside marsh species, and decreased species richness. Effects drying will have on one dominant forest tree, velvet ash, is unclear. Increase in the frequency of large floods would potentially increase forest density and decrease average tree age and diameter. Correlations between functional traits of Verde River plants and hydrologic gradients are consistent with "leaf economics," or the axis of resource capture, use, and release, as the primary strategic trade-off for plants. This corresponds to the competitor-stress tolerator gradient in Grime's life history strategy theory. Plant height was also a strong indicator of hydrologic condition, though it is not clear from the literature if plant height is independent enough of leaf characteristics on a global scale to be considered a second axis. Though the ecohydrologic relationships are approached from different perspectives, the results of the two papers are consistent if interpreted together. The species that are currently dominant in the near-channel Verde River floodplain are tall, broad-leaf trees, and the species that are predicted to become more dominant in the case of the river drying are shorter trees or shrubs with smaller leaves. These results have implications for river and water management, as well as theoretical ecology.
ContributorsHazelton, Andrea Florence (Author) / Stromberg, Juliet C. (Thesis advisor) / Schmeeckle, Mark W (Committee member) / Franklin, Janet (Committee member) / Arizona State University (Publisher)
Created2011
Description
As an industrial society, humans have increasingly separated agricultural processes from natural ecosystems. Many areas of the Southwestern US, however, maintain traditional practices that link agricultural systems to the natural environment. One such practice, diverting river water into fields via earthen irrigation canals, allows ditch water to recharge groundwater and riparian vegetation to prosper along canal banks. As there is growing interest in managing landscapes for multiple ecosystem services, this study was undertaken to determine if irrigation canals function as an extension of the riparian corridor. I was specifically interested in determining if the processes within semi-arid streams that drive riparian plant community structure are manifested in earthen irrigation ditches. I examined herbaceous and woody vegetation along the middle Verde River, AZ, USA and three adjacent irrigation ditches across six months. I also collected sieved hydrochores--seeds dispersing through water--within ditches and the river twelve times. Results indicate that ditch vegetation was similar to streamside river vegetation in abundance (cover and basal area) due to surface water availability but more diverse than river streamside vegetation due to high heterogeneity. Compositionally, herbaceous vegetation along the ditch was most similar to the river banks, while low disturbance fostered woody vegetation along the ditches similar to high floodplain and river terrace vegetation. Hydrochore richness and abundance within the river was dependent on seasonality and stream discharge, but these relationships were dampened in the ditches. Species-specific strategies of hydrochory, however, did emerge in both systems. Strategies include pulse species, which disperse via hydrochory in strict accordance with their restricted dispersal windows, constant species, which are year round hydrochores, and combination species, which show characteristics of both. There was high overlap in the composition of hydrochores in the two systems, with obligate wetland species abundant in both. Upland species were more seasonally constant and abundant in the ditch water than the river. The consistency of river processes and similarity of vegetation suggest that earthen irrigation ditches do function as an extension of the riparian corridor. Thus, these man-made irrigation ditches should be considered by stakeholders for their multiple ecosystem services.
ContributorsBetsch, Jacqueline Michelle (Author) / Stromberg, Juliet C. (Thesis advisor) / Hall, Sharon J (Committee member) / Merritt, David M. (Committee member) / Arizona State University (Publisher)
Created2010