Drivers of variability in water use of native and non-native urban trees in the greater Los Angeles area

Little is known about the factors that influence water use in urban trees, although it is generally accepted that they will have higher water loss than trees in natural forests. To contribute to a better understanding of the complex interactions involved, two common Los Angeles area species, the native, riparian California sycamore (Platanus racemosa) and the Mediterranean Canary Island pine (Pinus canariensis) were studied at four urban sites that spanned a coastal-to-inland gradient and that reflected a range of management intensities and climates. At each site, sap flow, weather conditions, leaf and soil nutrients and isotopic composition, and hydraulic conductance were measured. Whole tree transpiration was similar in the two species when sufficient water was available, but when water was limiting, the Canary Island pine was able to reduce transpiration significantly, in contrast to the sycamore. In the California sycamore, site-to-site differences in sap flux and water use were likely due to nutrient availability. For the pine, in contrast, most of the site-to-site variability in water use was due to differences in water availability.