HR: 14:50h
AN: B23E-05    [Abstracts]
TI: Drivers of Variability in Water Use of Native and Non-native Urban Trees in the Greater Los Angeles Area
AU: * McCarthy, H R
EM: heather.mccarthy@uci.edu
AF: University of California, Irvine, Department of Earth System Science, Irvine, CA 92697- 3100, United States
AU: Pataki, D E
EM: dpataki@uci.edu
AF: University of California, Irvine, Department of Earth System Science, Irvine, CA 92697- 3100, United States
AU: Pataki, D E
EM: dpataki@uci.edu
AF: University of California, Irvine, Department of Ecology and Evolution, Irvine, CA 92697- 3100, United States
AB: A number of cities, including Los Angeles, have started programs aimed at increasing urban tree cover, due to growing recognition that urban trees can mitigate urban heat island effects, storm water runoff, atmospheric CO₂ emissions and pollution, and energy expenditures. There is considerable interest in trying to quantify the magnitude of these tree-induced benefits, yet water use and water relations of urban trees have rarely been studied. Urban trees are exposed and presumably adapted to a different set of growing conditions than natural trees, including growth-enhancing environmental alterations such as irrigation and fertilization, but also detrimental conditions like increased ozone and restricted rooting area. In order to study the factors which control whole tree water use of common species in the Los Angeles Basin urban forest, four sites in Los Angeles and Orange County have been instrumented with sap flow and meteorological sensors. These sites allow comparisons of the water use of the same species under different environmental conditions: urban vs. non- urban, coastal vs. inland climates, and comparisons of native vs. non-native species. We found that over a similar vapor pressure deficit (daytime average 0.5-3.5 kPa; VPD) range, California native sycamores in the inland urban site exhibited far higher (up to 3 times) rates of daily sap flow (g cm^-2 d^-1) than sycamores in an inland non-urban (natural riparian, non-irrigated) site. However daily sap flow rates of sycamores at an urban coastal site, where VPD is generally lower (daytime average <1.2 kPa), were much lower than in the inland urban site even at the same VPD. In contrast, Canary Island pines showed lower daily sap flow rates over the same VPD range at an inland, urbanized site in comparison to a coastal, irrigated urban site. These differing behaviors in contrasting environments could result from differences in a number of allometric or hydraulic properties. In order to determine what drives the observed differences we are also measuring leaf area, plant water sources, vulnerability to cavitation, and leaf nutrient and isotopic composition. Our observations thus far reinforce the idea that measurements of natural forests cannot accurately predict the physiological responses and water relations of urban trees.
DE: 0493 Urban systems
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1834 Human impacts
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting