236 to be 0.12 W m−1°C–1 (at the time of greatest surface tempera- ture) in a partially moist system in a semiarid climate. Except for landscape irrigation, moisture inputs into landscape soils in Phoenix are extremely low and soils are normally dry. Montague and Kjelgren (2004) report that their soil was generally moist at the mulch–soil interface. Because moisture content is well known to affect soil thermal conductivity, differences between these values may be attributed to differing thermal and moisture regimes in each climate. It is generally believed that use of mulch conserves soil mois- ture by increasing boundary layer resistance to evaporative water loss and increasing water infiltration (Brady and Weil 2002) and many studies support this supposition about organic (Ashworth and Harrison 1983; Smith and Rakow 1992; Kraus 1998; Pick- ering et al. 1998; Iles and Dosmann 1999) and inorganic mulches (Smith and Rakow 1992; Kraus 1998). Li (2003) found that gravel–sand mulches reduced cumulative soil water loss by ap- proximately 10 mm (0.4 in) after 14 days. In comparison, we found that after 22 days, PPR and LTT mulches reduced cumu- lative soil water loss by approximately 25 mm (1 in), whereas LTT mulch reduced water loss by approximately 40 mm (1.6 in). CONCLUSION The ability of organic mulches to modify above- and below- ground landscape thermal environments has many implications and applications. We have shown that organic mulches can be used in the hot and arid climate of the desert southwest to con- serve soil moisture and protect landscape plant rhizosphere from soil temperatures in excess of 40°C (104°F). We have shown that organic mulches lower high soil temperature extremes by resist- ing the influx of radiant heat energy into landscape soil. More- over, these findings suggest that organic mulches may be used as an urban heat island management strategy, particularly in arid, desert southwest cities where urban heating is a nighttime phe- nomenon (Baker et al. 2002). Although organic mulches are not the normative mulch used in the desert southwest by landscape managers, our research showed that use of organic mulch in a hot desert climate can be more effective than inorganic mulches to ameliorate landscape soil thermo- and hydrodynamics. Future studies could determine how differential landscape irrigation re- gimes affect organic mulch thermal conductivity and how or- ganic mulches might affect soil carbon and nitrogen chemistry and landscape plant resiliency to desert climate extremes. Acknowledgments. We are grateful to the International Society of Arboriculture and the John Z. Duling TREE Fund for the fund- ing to conduct this research project. Singer and Martin: Effect of Landscape Mulches Ashworth, S., and H. Harrison. 1983. Evaluation of mulches for use in the home garden. HortScience 18:180–182. Baker, L.A., A.J. Brazel, N. Selover, C.A. Martin, N. McIntyre, F.R. Steiner, A. Nelson, and L. Musacchio. 2002. Urbanization and warm- ing of Phoenix (Arizona, USA): Impacts, feedbacks and mitigation. Urban Ecosystems 6:188–203. Brady, N.C., and R.R. Weil. 2002. The Nature and Properties of Soils. Prentice Hall, Upper Saddle River, NJ. Holman, J.P. 1986. Heat Transfer. McGraw-Hill Book Company, New York, NY. Iles, J.K., and M.S. Dosmann. 1999. Effect of organic and mineral mulches on soil properties and growth of Fairview Flame red maple trees. Journal of Arboriculture 25:163–167. Kraus, H.T. 1998. Effects of mulch on soil moisture and growth of desert willow. HortTechnology 8:588–590. Li, X.-Y. 2003. Gravel-sand mulch for soil and water conservation in the semiarid loess region of northwest China. CATENA 52:105–127. Litzow, M., and H. Pellett. 1983. Influence of mulch materials on growth of green ash. Journal of Arboriculture 9:7–11. Martin, C.A. 2001. Landscape water use in Phoenix, Arizona. Desert Plants 17:26–31. Montague, T., and R. Kjelgren. 2004. Energy balance of six common landscape surfaces and the influence of surface properties on gas exchange of four containerized species. Scientia Horticulturae 100: 229–249. Montague, T., R. Kjelgren, and L. Rupp. 1998. Surface energy balance affects gas exchange of three shrub species. Journal of Arboriculture 24:254–262. ———. 2000. Surface energy balance affects gas exchange and growth of two irrigated landscape tree species in an arid climate. Journal of the American Society for Horticultural Science 125:299–309. Montague, T., C. McKenney, M. Maurer, and B. Winn. 2007. Influence of irrigation volume and mulch on establishment of select shrub species. Arboriculture and Urban Forestry 33:202–209. Pickering, J.S., A.D. Kendle, and P. Hadley. 1998. The suitability of composted green waste as an organic mulch: Effects on soil moisture retention and surface temperature. Acta Horticulturae 469:319–324. Skroch, W.A., M.A. Powell, T.E. Bilderback, and P.H. Henry. 1992. Mulches: Durability, aesthetic value, weed control, and temperature. Journal of Environmental Horticulture 10:43–45. Smith, A.M., and D.A. Rakow. 1992. Strategies for reducing water input in woody landscape plantings. Journal of Arboriculture 18:165–170. U.S. Government. 2002. Healthy Forests Initiative. www.healthyforest- s.gov/initiative/index.html (accessed 5/21/07). van Donk, S.J., and E.W. Tollner. 2001. Measuring and modeling heat transfer parameters in mulches. Acta Horticulturae 566:447–453. van Wesemael, B., J. Poesen, C.S. Kosmas, N.G. Danaloatos, and J. Nachtergaele. 1996. Evaporation from cultivated soils containing rock fragments. Journal of Hydrology 182:65–82. Chris A. Martin (corresponding author) Arizona State University Applied Biological Sciences 7001 East Williams Field Road Building 130 Mesa, AZ 85212, U.S.
[email protected] LITERATURE CITED Abu-Hamdeh, N.H., and R.C. Reeder. 2000. Soil thermal conductivity: Effects of density, moisture, salt concentration, and organic matter. Journal American Society of Soil Science 64:1285–1290. Arizona Meteorological Network (AZMET). Extension Biometeorology Program. College of Agriculture. University of Arizona Cooperative Extension. http://ag.arizona.edu/azmet/ (accessed 10/30/07). ©2008 International Society of Arboriculture Catherine K. Singer Arizona State University Applied Biological Sciences 7001 East Williams Field Road Building 130 Mesa, AZ 85212, U.S.
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