Continued growth in the arid southwestern United States is placing greater demand on available water resources. Much of this growth is in sprawling metropolises where water is used outdoors to support urban landscapes (Devitt et al., 2008; Litvak et al., 2017; St. Hilaire et al., 2008). In the case of the Las Vegas Valley, NV, 60% of the water is used in the residential sector [Southern Nevada Water Authority (SNWA), 2018] and 66% of that is used to irrigate urban landscapes (Devitt et al., 2008). As such, water districts such as SNWA have focused much attention on reducing the outdoor water use component to achieve critical balance between supply and demand.
ET of landscape vegetation varies based on species (size, cover, leaf area index), edaphic and climatic conditions, water quality, and physiological mechanisms that regulate water loss (Devitt et al., 1994; Jarvis and McNaughton, 1986; Nisbet, 2005; Peters et al., 2011; Stevenson, 1989; Wullschleger et al., 2001), however the overall driving force in arid environments is simply how much water is made available to plants (Devitt et al., 1994). In southern Nevada, annual precipitation is less than 11 cm per year; thus, urban landscapes need significant amounts of irrigation water annually. Although large water savings can always be achieved by deficit irrigating, such an approach should not be implemented on a long-term basis, especially if the irrigation water contains significant levels of soluble salts, as is the case for Colorado River water (EC 1.05 dS·m−1) and reuse water (≈2.00 dS·m−1) used to irrigate landscapes in southern Nevada (Devitt et al., 2007) because it will lead to significant salt accumulation.
Trees play a significant role in urban landscapes by providing beauty, shade, and cooling (McPherson et al., 1989), but they also can consume significant amounts of water (Pataki et al., 2011). In Los Angeles, it is estimated that trees cover more than 13,000 ha, totaling more than 10 million trees (McPherson et al., 2008, 2011) comprising more than 140 species (Nowak et al., 2010), many of which are not native to the region. Although selecting xeric trees for urban landscapes is often recommended in arid environments, Sun et al. (2012) reported that woody species categorized as low water users from xeric habitats actually consumed almost as much water as mesic plants when grown under well-watered conditions.
ET of urban landscape trees have been estimated using various techniques. Closing water balances using lysimeters can be accurate, but these typically have been limited to small trees (Devitt et al., 1994; Levitt et al., 1995), whereas water use of trees growing in a landscape setting have typically been assessed by using sap flow sensors (Litvak et al., 2012; Pataki et al., 2011; Peters et al., 2010) in conjunction with assessments of environmental demand but typically not with a tight water balance that accounts for irrigation, evaporation, and drainage components (Litvak and Pataki, 2016; Pataki et al., 2011). Other techniques such as eddy covariance (Peters et al., 2011) and remote sensing (Nouri et al., 2016) are typically employed over larger scales (urban forest as opposed to the individual tree) but still require field validation to verify accuracy (typically using a soil water balance approach such as that described by Nouri et al., 2013). Unfortunately closing water balances in the field requires estimating drainage, which can be challenging and requires using such techniques as drainage flux meters (Devitt et al., 2018), chloride balance (Devitt, 1989), or large in situ lysimeters (Sun et al., 2012).
ET of turfgrass has been extensively studied over the past 70 years (Bowman and Macauly, 1991; Brown et al., 2004; DaCosta and Huang, 2006; Devitt et al., 1992; Gibeault et al., 1985; Litvak and Pataki, 2016; Penman, 1948; Schiavon et al., 2017; Shearman and Beard, 1973), and although ET of urban landscape trees have been studied over the past 30 years (Devitt et al., 1993, 1994, 1995; Levitt et al., 1995, 2017; Pataki et al., 2011; Sun et al., 2012; Zajicek and Heilman, 1991), few studies have made direct comparisons between landscape trees and turfgrass with regard to water use (Devitt et al., 1995; Litvak et al., 2014, 2017; Peters et al., 2011).
The objective of this study was to quantify the ET of 10 landscape trees and two turfgrass species using a soil water balance approach to determine tree grass water use ratios and what this might mean in terms of water use trade-offs in the landscape. In addition, we quantified transpiration (T) using sap-flow sensors, allowing us to indirectly estimate evaporation (E) by difference (E = ET – T). The trees were planted in a high-density setting, allowing us to assess the impact high-density planting (individual % tree cover) had on ET (based on basal canopy area) and E.
Allen, R., Pereira, L.S., Raes, D. & Smith, M. 1998 Crop evapotranspiration: Guidelines for computing crop requirements. FAO Irrigation and Drainage 56
Berdanier, A.B., Miniat, C.F. & Clark, J.S. 2016 Predictive models for radial sap flux variation in coniferous, diffuse-porous and ring porous temperate trees Tree Physiol. 36 932 941
Bonachela, S., Orgaz, F.L., Villablobos, F.J. & Fereres, E. 1999 Measurement and simulation of evaporation from soil in olive orchards Irrig. Sci. 18 205 211
Brown, C., Devitt, D.A. & Morris, R.L. 2004 Water use and physiological response of tall fescue turf to water deficit irrigation in an arid environment HortScience 39 388 393
Calder, I.R. 1990 Evaporation in the uplands. Wiley, Chichester, UK
DaCosta, M. & Huang, B. 2006 Minimum water requirements for creeping, colonial and velvet bentgrass under fairway conditions Crop Sci. 46 81 89
Devitt, D.A., Morris, R.L. & Bowman, D.C. 1992 Evapotranspiration, crop coefficients, and leaching fractions of irrigated desert turfgrass systems Agron. J. 84 717 723
Devitt, D.A., Berkowitz, M., Schulte, P.J. & Morris, R.L. 1993 Estimating transpiration for three woody ornamental tree species using stem-flow gauges and lysimetry HortScience 28 320 322
Devitt, D.A., Morris, R.L. & Neuman, D.S. 1994 Evapotranspiration and growth response of three woody ornamental species placed under varying irrigation regimes J. Amer. Soc. Hort. Sci. 119 452 457
Devitt, D.A., Neuman, D.S., Bowman, D.C. & Morris, R.L. 1995 Comparative water use of turfgrasses and ornamental trees in an arid environment J. Turfgrass Mgt. 1 47 63
Devitt, D.A., Sala, A., Smith, S.D., Cleverly, J., Shaulis, L.K. & Hammett, R. 1998 Bowen ratio estimates of evapotranspiration for Tamarix ramosissima stands on the Virgin River in southern Nevada Water Resour. Res. 34 2407 2414
Devitt, D.A., Lockett, M., Morris, R.L. & Bird, B.M. 2007 Spatial and temporal distribution of salts on fairways and greens irrigated with reuse water Agron. J. 99 692 700
Devitt, D.A., Carstensen, K. & Morris, R.L. 2008 Residential water savings associated with satellite-based ET irrigation controllers J. Irrig. Drain. Eng. 134 74 82
Devitt, D., Bird, B., Lyles, B., Fenstermaker, L., Jasoni, R., Strachan, S., Arnone, J., Biondi, F., Mensing, S. & Saito, L. 2018 Assessing near surface hydrologic processes and plant response over a 1600 m mountain valley gradient in the Great Basin, NV, USA Water 10 4 1558 1566
Gibeault, V.A., Meyer, J.L., Youngner, V.B. & Cockerham, S.T. 1985 Irrigation of turfgrass below replacement of evapotranspiration as a means of water conservation: Performance of commonly used turfgrass. Proc. Intl. Turgrass Res. Conf. Avignon France 5:347–356
Granier, A., Huc, R. & Barigali, S.T. 1996 Transpiration of natural rain forest and its dependence on climatic factors Agr. For. Meteorol. 78 19 29
Kjelgren, R., Montague, T. & Beeson, R. 2005 Water use and stomatal behavior of sweetgum (Liquidambar styraciflua L.) relative to reference evaporation in three contrasting regions Acta Hort. 664 353 360
Leskys, A., Devitt, D.A., Morris, R.L. & Verchick, L.S. 1999 Response of tall fescue to saline water as influenced by leaching fractions and irrigation uniformity distributions Agronomy 91 409 416
Litvak, E., McCarthy, H.R. & Pataki, D.E. 2012 Transpiration sensitivity of urban trees in a semi-arid climate is constrained by xylem vulnerability to cavitation Tree Physiol. 32 373 388
Litvak, E., Bijoor, N.S. & Pataki, D.E. 2014 Adding trees to irrigated turfgrass lawns may be a water-saving measure in semi-arid environments Ecohydrology 7 1314 1330
Litvak, E. & Pataki, D.E. 2016 Evapotranspiration of urban lawns in a semi-arid environment: An in-situ evaluation of microclimatic conditions and watering recommendations J. Arid Environ. 134 87 96
Litvak, E., Manago, K.F., Hogue, T.S. & Pataki, D.E. 2017 Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale Water Resour. Res. 53 4236 4252
McPherson, E.G., Simpson, J.R. & Livingston, M. 1989 Effects of three landscapes on residential energy and water use in Tucson, Arizona Energy Build. 13 127 138
McPherson, E.G., Simpson, J.R., Xiao, Q. & Wu, C. 2008 Los Angeles 1 million tree canopy cover assessment. General Technical Report PSW-GTR-207. U.S. Dept. of Agr., For. Serv. Pac. Southwest Res. Stn
Nisbet, T. 2005 Water use of trees. FCIN065. Forestry Commission, Edinburgh, Scotland
Nouri, H., Beecham, S., Kazemi, F. & Hassanli, A.M. 2013 A review of ET measurement techniques for estimating the water requirements of urban landscape vegetation Urban Water J. 10 247 259
Nouri, H., Glenn, E.P., Beecham, S., Boroujeni, S.C., Sutton, P., Alaghmand, S., Norri, B. & Nagler, P. 2016 Comparing three approaches of evapotranspiration estimation in mixed urban vegetation: Field based remote sensing based and observational-based methods Remote Sens. 8 6 492
Nowak, D.J., Hoehn, R.E.I., Crane, D.E., Weller, L. & Davila, A. 2010 Assessing urban forest effects and values, Los Angeles urban forest. Resour. Bull. NRS-47. U.S. Department of Agriculture, Forest Service, Northern Research Station, Newton Square, PA
Pataki, D.E., McCarthy, H.R., Litvak, E. & Pincetl, S. 2011 Transpiration of urban forests in the Los Angeles metropolitan area Ecol. Appl. 21 661 677
Peters, E.B., McFadden, J.P. & Montgomery, R.A. 2010 Biological and environmental controls on tree transpiration in a suburban landscape J. Geophys. Res. 115 G04006
Peters, E.B., Hiller, R.V. & McFadden, J.P. 2011 Seasonal contributions of vegetation types to suburban evapotranspiration J. Geophys. Res. 116 GO1003
Schiavon, M., Pedroza, A., Leinauer, B., Suarez, D.L. & Baird, J.H. 2017 Varying evapotranspiration and salinity level of irrigation water influence soil quality and performance of perennial ryegrass (Lolium perenne L.) Urban For. Urban Green. 26 184 190
Schwankl, L.J., Prichard, T.L., Hanson, B.R. & Elkins, R.B. 2007 ANR Publication 8212, University of California Cooperative Extension
Southern Nevada Water Authority 2018 Restricting outdoor water use. 1 Feb. 2018. <https://www.snwa.com/importance-of-conservation/restricting-outdoor-water-use/index.html>
Shearman, R.C. & Beard, J.B. 1973 Environmental and cultural preconditioning effects on the water use rate of Agrostis palustris Huds., cultivar Penncross Crop Sci. 13 424 427
St. Hilaire, R., Arnold, M.A., Wilkerson, D.C., Devitt, D.A., Hurd, B.H., Lesikar, B.J., Lohr, V.I., Martin, C.A., McDonald, G.V., Morris, R.L., Pittenger, D.R., Shaw, D.A. & Zoldoske, D.F. 2008 Efficient water use in residential urban landscapes HortScience 43 2081 2092
Sun, H., Kopp, K. & Kjelgren, R. 2012 Water-efficient urban landscapes: Integrating different water use categorizations and plant types HortScience 47 254 263
Testi, L., Villalobos, F.J. & Orgaz, F. 2004 Evapotranspiration of a young irrigated olive orchard in southern Spain Agr. For. Meteorol. 121 1 18
Wright, L., Devitt, D.A., Young, M.H., Gan, J., Vanderford, B., Snyder, S. & McCullough, M. 2012 Fate and transport of 14 pharmaceutical and personal care products in an irrigated turfgrass system Agron. J. 104 1244 1254
Wullschleger, S., Hanson, P.J. & Todd, D.E. 2001 Transpiration from a multi-species deciduous forest as estimated by xylem sap flow techniques For. Ecol. Mgt. 143 205 213
Wynne, T. 2019 Tree to grass water use ratios; assessing turfgrass high water use in the urban landscape. MS thesis, Univ. of Nevada, Las Vegas. 30 Nov. 2019. <https://digitalscholarship.unlv.edu/thesesdissertations/3705?utm_source=digitalscholarship.unlv.edu%2Fthesesdissertations%2F3705&utm_medium=PDF&utm_campaign=PDFCoverPages>
Zajicek, J. & Heilman, J. 1991 Transpiration by crepe myrtle cultivars surrounded by mulch, soil and turfgrass surfaces HortScience 26 1207 1210