Arboriculture & Urban Forestry 32(5): September 2006 211 Aldrich et al. 2003) and known to hybridize with at least seven other oak species (ilicifoia, imbricaria, palustris, phel- los, shumardii, velutina, [Palmer 1948], Q ellipsoidalis [Ho- kanson et al. 1993]). In the Hokanson et al. (1993) study, Q. rubra and the Q. rubra × Q. ellipsoidalis hybrids could not be distinguished by morphologic traits, but morphologic traits could be used to identity Q. rubra and Q. ellipsoidalis (Tom- linson et al. 2000). In our study, although the Q rubra mother trees and their progeny appeared morphologically true to type, it is likely that hybrids would have been undetected. Similarly, hybrids or gene flow could be contributing to the within-family variation in morphology and water use of Q. palustris and Q. macrocarpa seedlings. We suggest that Q, macrocarpa, Q. palustris, Q. prinus, Q. rubra, Q. shumardii, and Q. velutina seedlings with high height-adjusted water use are better adapted to drier sites than are those seedlings with low height-adjusted water. Untested is the assumption is that those seedlings with xeric morphol- ogy and high height-adjusted water use also have greater drought tolerance. Clonal material is needed to confirm the genetic basis of the differing within species water use char- acteristics and the relationship among seedling morphology, water use characteristics, and drought tolerance. Clonal propagation of seedlings with xeric and mesic water use char- acteristics and morphologies identified in experiment 4 is being done at The Ohio State University. In conclusion, xeric and mesic seedling morphology and water use characteristics were described for six oak species. Xeric morphology was evidenced by relatively slower height growth and lower shoot:root ratios than seedlings with mesic morphology. A xeric water use pattern was characterized by relatively high height-adjusted water use (g water used cm–1 height day–1). Mesic water use seedlings were characterized by low height-adjusted water use and more rapid height growth. It may be possible to use seedling morphology and water use characteristics to increase “dominance probability” by better matching planting stock with planting sites by ac- knowledging within-species differences in growth and water use characteristics. If xeric water use pattern, morphology, and greater drought tolerance are linked, then nursery stock most suited to stressful urban forestry use will take longer to produce and use more water during production than seedlings with mesic characteristics. Consumers who specify planting stock with the xeric growth and water use characteristics should be willing to compensate nursery producers for their higher production costs and longer rotation times, because they will receive nursery stock with better “fitness to pur- pose.” LITERATURE CITED Abrams, M.D. 1990. Adaptions and responses to drought in Quercus species of North America. Tree Physiology 7: 227–238. Aldrich, P.R., B.R. Parker, C.H. Michler, and J. Fomero- Severson. 2003. Whole-tree silvic identification and the microsatellite genetic structure of a red oak species com- plex in an Indiana old-growth forest. Canadian Journal of Forest Research 33:2228–2237. Arnold, M.A., and D.K. Struve. 1993. Root distribution and mineral uptake of coarse-rooted trees grown in cupric hydroxide-treated containers. HortScience 28:988–992. Bourdeau, P. 1954. Oak seedling ecology determining segre- gation of species. Ecological Monographs 24:297–320. Bunce, J.A., L.N. Miller, and B.F. Chabot. 1977. Competitive exploitation of soil water by five eastern North American tree species. Botanical Gazette 138:168–173. Burger, W.C. 1975. The species concept in Quercus. Taxon 24:45–50. Dickson, R.E., and P.T. Tomlinson. 1996. Oak growth, de- velopment and carbon metabolism in response to water stress. Annales Des Sciences Forestieres 53:181–196. Drunasky, D., and D.K. Struve. 2005. Quercus macrocarpa and Q. prinus physiological and morphological responses to drought stress and their potential for urban forestry. Urban Forestry and Urban Greening 4:13–22. Farmer, R.E. Jr. 1979. Comparative analysis of 1st-year growth in six deciduous tree species. Canadian Journal of Forest Research 10:35–41. Farmer, R.E. Jr., M.A. Barnhill, and J.C. Rennie. 1981. Variation in 10-year growth of northern red oak from provenances in the Tennessee valley, pp. 100–115. In Pro- ceedings of the North Center Tree Improvement Confer- ence, Madison, WI. Fowells H.A. 1975. Silvics of Forest Trees of the United States. USDA Forest Service Agriculture Handbook No. 271. Gonzalez, R.A., and D.K. Struve. 1992. A computer- controlled drip irrigation system for container plant pro- duction. HortTechnology 2:402–407. Guttman, S.I., and L.A. Weigt. 1988. Electrophoretic evi- dence of relationships among Quercus (oaks) of eastern North America. Canadian Journal of Botany 67:339–351. Hanson, P.J., R.E. Dickson, J.G. Isebrands, T.R. Crow, and R.K. Dixon. 1986. A morphological index of Quercus seedling ontogeny for use in studies of physiology and growth. Tree Physiology 2:273–281. Harlow, W.M., E.S. Harrar, and F.M. White. 1979. Textbook of Dendrology. 6th Ed. McGraw-Hill, New York, NY. Hokanson, S.C., J.G. Isebrands, R.J. Jensen, and J.F. Han- cock. 1993. Isozyme variation in oaks of the Apostle Is- lands in Wisconsin: genetic structure and levels of in- breeding in Quercus rubra and Q. ellipsoidalis (Faga- ceae). American Journal of Botany 80:1349–1357. Houston, D.B. 1983. Stand and seed source variation in per- oxidases isozymes of Quercus rubra L. Silvae Genetica 32:59–63. ©2006 International Society of Arboriculture
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