Plant water-use efficiency as a metric of urban ecosystem services

Abstract

Trees in urban ecosystems are valued for shade and cooling effects, reduction of CO2 emissions and pollution, and aesthetics, among other benefits. However, in arid and semiarid regions, urban trees must be maintained through supplemental irrigation. In these regions it is desirable to identify tree species that are especially efficient in the balance between water loss and carbon uptake. We used a common-garden approach to compare water-use efficiency (WUE) at leaf and tree scales for commonly planted, nonnative tree species in the Los Angeles Basin (California, USA), in order to evaluate WUE as a metric of the trade-off between water use and growth in urban trees. Leaf-level gas exchange, sap flux density, leaf δ13C, and stem growth measurements were conducted on eight species within the Los Angeles County Arboretum: Brachychiton discolor, B. populneus, Eucalyptus grandis, Ficus microcarpa, Jacaranda chelonia, Gleditsia triacanthos, Lagerstroemia indica, and Koelreuteria paniculata. We found species wit...