Journal of Arboriculture 31(2): March 2005 87 Although roots were found at all angles between the horizontal and vertical planes, root distribution measure- ments indicate that coast live oak developed roots with a stronger vertical than horizontal orientation. Although root distribution can vary with soil conditions, previous reports have described a largely horizontal orientation for tree root systems (Perry 1982; Wilson 1984). Here, results suggest that coast live oak has the potential to develop a root system with a strong vertical component. Root depth and distance were found to be independent of irrigation treatments: the application of irrigation water did not substantially change root distribution. This result suggests that the root distribution pattern for coast live oak became established largely during the first year after planting. Although root diameter and extension growth continued in subsequent years, root distribution at depth did not change after the first year. CONCLUSION In summary, irrigation did not enhance trunk diameter growth of coast live oak, valley oak, or blue oak. After a 1- year establishment period, each of these species was found to grow at the same rate with or without irrigation. Trunk diameter growth was significantly different for the three oak species, with coast live oak being largest, followed by valley oak and blue oak. Coast live oak was found to apportion approximately 2.6 times more biomass to shoots than roots (on average), and increasing irrigation volume resulted in a significant increase in shoot:root ratio. Roots of coast live oak developed a stronger vertical than horizontal orienta- tion, and root distribution patterns did not change in response to irrigation treatments. LITERATURE CITED Burger, D.W., G.W. Forister, and R. Gross. 1997. Short- and long-term effects of treeshelters on the root and stem growth of ornamental trees. J. Arboric. 23(2):49–56. Costello, L.R., and K.S. Jones. 2000. A Guide to Estimating the Irrigation Water Requirements of Landscape Plantings in California. California Department of Water Resources, Sacramento, CA. 150 pp. Craul, P.J. 1999. Urban Soils: Applications and Practices. John Wiley and Sons, New York, NY. 366 pp. Daddow, R.L., and G.E. Warrington. 1983. Growth-Limiting Soil Bulk Densities As Influenced by Soil Texture. USDA-FS Watershed Systems Development Group Rpt. WSDG-TN- 00005. USDA Forest Service, Fort Collins, CO. 17 pp. Gilman, E.F. 2001. Effect of nursery production method, irrigation, and inoculation with mycorrhizae-forming fungi on establishment of Quercus virginiana. J. Arboric. 27(1):30–38. Gilman, E.F., R.J. Black, and B. Dehgan. 1998. Irrigation volume and frequency and tree size affect establishment rate. J. Arboric. 24(1):1–9. Gilman, E.F., A. Stodola, and M.D. Marshall. 2002. Root pruning but not irrigation in the nursery affects live oak root balls and digging survival. J. Environ. Hortic. 20(2):122–126. Harris, R.W. 1992. Root-shoot ratios. J. Arboric. 18(1):39–41. Lindsey, P., and N. Bassuk, 1991. Specifying soil volumes to meet water needs of mature trees in containers. J. Arboric. 17:141–149. McCreary, D.D. 1993. How to Grow California Oaks. University of California Integrated Hardwood Range Management Program, Berkeley, CA. ———. 2001. Regenerating Rangeland Oaks in California. University of California Agriculture and Natural Resources Communication Services Publication No. 21601. University of California, Davis, CA. 62 pp. McCreary, D.D., L.R. Costello, J. Tecklin, K.S. Jones, and D. Labadie. 2002. The effects of irrigation and aboveground protection on the field performance of three species of oaks. In Proceedings of the Fifth Oak Symposium: Oaks in California’s Changing Landscape. 22–25 October 2001, San Diego, CA. USDA Forest Service Pacific Southwest Research Station Gen. Tech. Rep. PSW-TR 184:387–395. Pavlik, B.M., P.C. Muick, S.G. Johnson, and M. Popper. 1992. Oaks of California. Cachuma Press, Los Olivos, CA. 184 p. Perry, T.O. 1982. The ecology of tree roots and the practical significance thereof. J. Arboric. 8:197–211. Standiford, R.B. 1999. Integrated Hardwood and Range Management Program: 7th Progress Report. University of California Agricultural and Natural Resources and Department of Forestry and Resource Management, Berkeley, CA. Swiecki, T.J., and E. Bernhardt. 1993. Factors Affecting Blue Oak Sapling Recruitment and Regeneration. Report for the California Department of Forestry and Fire Protection Strategic Planning Program. California Department of Forestry, Sacramento, CA. 132 p. Wilson, B.F. 1984. The Growing Tree (rev. ed). University of Massachusetts Press, Amherst, MA. Acknowledgments. The authors gratefully acknowledge the E.J. Slosson Endowment for grant support. We thank Zac Mousli, Leo Dumont, and Santiago Aldana (BAREC) for assistance in installing and maintaining the research plot; Tom Bressan, Urban Farmer Store, San Francisco, California, for irrigation system design; and Carol Adams and Christiana Drake (University of California, Davis) for statistical support. ©2005 International Society of Arboriculture
March 2005
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