Arboriculture & Urban Forestry 33(5): September 2007 357 particular location. Equally important is the need to select proven trees for large-scale planting within a community. Using tree species or genera that are poorly adapted, while creating short-term diversity, will not contribute to long-term stability. However, even in the harsh sites that occur in South Dakota, there appears to be enough choices for expanding the use of other genera such as corktrees (Phellodendron spp.) that can be found thriving in residents’ lawns but is rarely used as a street tree in the state. As Bassuk (1990) pointed out, although only a few species make up the majority of street trees, there is also a large number of species, often more than 50, that comprise the entire street tree populations. Some of these may be minor species as a result of objectionable fruit or other attributes; others may be site-sensitive and only able to thrive on a few select sites. Even given this as a consideration, the diversity of species and genera could be expanded in many communi- ties. Gerhold et al. (1993) identified as potential street trees more than 70 species representing 37 genera and 19 families, although the adaptability of each would need to be checked for adaptation to the local conditions. A 10% rule for genera would still provide a sufficient plant palette for even a harsh climate such occurs on the Northern Plains. McPherson et al. (2003) identifies 92 species in 21 different genera as decidu- ous trees suitable for planting in zone 4, although some would be very marginal considering the spring and autumn extreme temperature fluctuations on the Northern Plains and not all the species listed are acceptable street trees. CONCLUSIONS Although many of the surveyed communities have significant available planting sites along their streets, merely planting genera other than ash will not provide stability because the present number is sufficiently great enough that the cost of removal of these trees during an emerald ash borer epidemic will be a major disruption to these cities. Because ash repre- sents a large proportion of the younger growing stock, the hazard will remain high for many decades or until the arrival of the insect into the state. Planting the available planting sites with a more diverse selection of genera, if adapted to the sites, will provide long- term stability as the ash population matures and is replaced. The present high hazard, a level that will be maintained for the foreseeable future, clearly points to the benefit of moni- toring and possible regulatory efforts at restricting the move- ment of ash firewood and logs into the state. The cost of removing these trees, even over an extended period, would have a major impact on the budgets of the state and communities and divert resources that could be used for other services. Acknowledgments. We thank the Master Gardeners of South Da- kota for their efforts in data collection and data entry. We also thank Coe Foss, Forest Health Program Administrator, South Dakota Di- vision of Resource Conservation and Forestry, for his critical review of the manuscript. LITERATURE CITED Arnold, H.F. 1980. Trees in Urban Design. New York, Van Nostrand Reinhold Company. 168 pp. Barker, P.A. 1975. Ordinance control of street trees. Journal of Arboriculture 1:212–216. Bassuk, N. 1990. Street tree diversity making better choices for the urban landscape, pp. 71–78. In Trees for the Nine- ties: Landscape Tree Selection, Testing, Evaluation and Introduction. Proc. 7th Conference Metropolitan Tree Im- provement Alliance. Lisle, IL, Morton Arboretum. Campana, R.J. 1999. Arboriculture: History and Develop- ment in North America. East Lansing, MI, Michigan State Press. 443 pp. Cappaert, D., D.G. McCullough, T.M. Poland, and N.W. Siegert. 2005. Emerald ash borer in North America: A research and regulatory challenge. American Entomolo- gist 51:152–165. Clark, J.R., N.P. Matheny, G. Cross, and V. Wake. 2003. A model of urban forest sustainability. Journal of Arboricul- ture 23:17–30. Cochran, W.G. 1977. Sampling Techniques. 3rd ed. New York, John Wiley & Sons. 428 pp. Coulson, R.N., and J.A. Witter. 1984. Forest Entomology. New York, John Wiley & Sons. 669 pp. Gerhold, H.D., W.N. Wandell, and N.L. Lacasse. 1993. Street Tree Factsheets. University Park, PA, Penn State. 132 pp. Gibbs, J.N., and D. Wainhouse. 1986. Spread of forest pests and pathogens in the Northern Hemisphere. Forestry 59: 141–153. Grey, G.W., and F.J. Deneke. 1986. Urban Forestry. 2nd ed. New York, John Wiley and Sons. 299 pp. Hermes, D., E. Rebek, D. Smitley, P. Bonello, and D. Cipol- lini. 2005. Interspecific variation in ash resistance to em- erald ash borer, pp. 33–38. In Emerald Ash Borer Re- search and Technology Development. Mastro, V., and Reason, R., Eds. FHTET-2004-15. Morgantown, VA, USDA For. Serv. Hogan, E.P. 1995. The Geography of South Dakota. Free- man, SD, Pine Tree Press. 190 pp. Johnson, W.T., and H.H. Lyon. 1988. Insects That Feed on Trees and Shrubs. Ithaca, NY, Cornell University Press. 556 pp. Kielbaso, J.J. 1990. Trends and issues in city forestry. Journal of Arboriculture 16:69–76. Kielbaso, J.J., and M.K. Kennedy. 1983. Urban forestry and entomology: A current appraisal, pp. 423–440. In Urban Entomology: Interdisciplinary Perspective. New York, Praeger Publishers. 493 pp. ©2007 International Society of Arboriculture
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