| Description |
Urbanization of the western United States has been associated with large-scale changes in the species composition and distribution of vegetation on the landscape. Among these changes include the afforestation of land within city boundaries with nonnative cultivars subject to markedly different atmospheric conditions compared to their native habitats and the introduction and expansion of nonnative tree species in riparian regions, both within city boundaries proper and in wild land riparian areas throughout the West. This dissertation is concerned with how these changes have impacted the water use and physiological behavior of tree species in these environments and the associated water use consequences of these changes at multiple temporal and spatial scales. Multiple sites within the Salt Lake Valley of northern Utah, USA, were instrumented with thermal dissipation probes for measuring sap flow. In addition, porometry, water potential, and other methods were used to further evaluate plant water relations and also the properties and functional status of xylem vasculature. In cultivated landscapes, I found that wood anatomy (ring- versus diffuse-porous xylem) constrained stomatal responses and associated rates of water loss to atmospheric vapor pressure deficit and that differential sensitivity was linked to vulnerability to xylem cavitation. The scaling of sap flux density data to whole-tree and stand water use in an unmanaged riparian forest and across sites in the Salt Lake City urban forest showed significant variation that was independent of native versus nonnative species status or wood anatomical characteristics. In addition, seasonality differences were observed with respect to the magnitude and timing of water fluxes that were linked to xylem cavitation vulnerability. The results reported here further increase our understanding of the physiology and water use behavior of trees in both urban and natural ecosystems and provide much needed information toward making informed management decisions that impact water resources in urban regions and riparian areas throughout the western US as well as semiarid regions elsewhere. |
