WATER-USE OF 2 LANDSCAPE TREE SPECIES IN TUCSON, ARIZONA

Although water conservation programs in the arid southwestern United S tates have prompted prudent landscaping practices such as planting low water use trees, there is little data on the actual water use of most species, The purpose of this study was to determine the actual water use of two common landscape tree species in Tucson, Ariz., and water u se coefficients for two tree species based on the crop coefficient con cept. Water use of oak (Quercus virginiana 'Heritage') and mesquite (P rosopis alba 'Colorado') trees in containers was measured from July to October 1991 using a precision balance. Water-use coefficients for ea ch tree species were calculated as the ratio of measured water use per total leaf area or per projected canopy area to reference evapotransp iration obtained from a modified FAO Penman equation. After accounting for tree growth, water-use coefficients on a total leaf area basis we re 0.5 and 1.0 for oak and mesquite, respectively, and on a projected canopy area basis were 1.4 and 1.6 for oaks and mesquites, respectivel y. These coefficients indicate that mesquites (normally considered xer ic trees) use more water than oaks (normally considered mesic trees) u nder nonlimiting conditions.