Arboriculture & Urban Forestry 33(4): July 2007 243 growth and of soil water content will provide a proper knowl- edge base to improve irrigation plans. LITERATURE CITED Balder, H., K. Ehlebracht, and E. Mahler. 1997. Strassen- bäume: Planen, Pflanzen, Pflegen am Beispiel Berlin. Patzer Verlag, Berlin. Befeldt, P. 1989. Begrenzender Faktor: Wasser. Deutscher Gartenbau 46:2778–2780. Brady, N.C. 1974. The Nature and Properties of Soils. Mac- millan Publishing Co., New York, NY. Figure 12. Illustration of the self-reinforcing cycle of tree degeneration. For optimal monitoring, diameter assessments should be car- ried out on a yearly basis. Monitoring of growth should be accompanied by soil water assessments to determine when supplemental irrigation is required for proper long-term de- velopment of urban trees. It is our belief that establishment of an “irrigation alarm system” is economically justified, because it is likely to re- duce tree mortality rates. Such a system will slightly increase the maintenance costs but strongly reduce the costs of tree establishment. CONCLUSIONS Both absolute and relative growth were considerably lower in nonirrigated street trees than in park trees of similar age (Bühler et al. 2006). To a wide extent, this finding is attrib- uted to differences in the soil water dynamic. Our results indicate that a large part of the precipitation never enters the mineral soil matrix in these 1.5 × 4m(4.95 × 13.2 ft) planting pits because of extensive interception by buildings, bark mulch, and by the tree crown itself. We think that a marginal expansion of the planting pit surface outside the crown drip zone would distinctly improve water infiltration. The water retention capacity of the planting pit substrate was variable but generally poor. One of the consequences was a high rate of water loss during the first days after precipitation or irrigation. It is recommended to improve the topsoil substrate with clay granules to counteract the excessive drainage caused by the coarse soil texture. Ex- panding the planting pit vertically with a subsoil substrate will likely help retain some of the drained water within reach of the roots. Furthermore, efforts to reach a higher homoge- neity in water retention within a series of planting pits will result in more homogenous long-term development of the trees. We suggest using maintenance irrigation to prevent death and degeneration of trees. Monitoring of stem diameter Bühler, O., C.N. Nielsen, and P. Kristoffersen. 2006. Growth and phenology of established Tilia cordata street trees in response to different irrigation regimes. Arboriculture & Urban Forestry 32:3–9. Clark, J.R., and R. Kjelgren. 1990. Water as a limiting factor in the development of urban trees. Journal of Arboricul- ture 16:203–208. Czerniawska-Kusza, I., G. Kusza, and M. Duzynski. 2004. Effect of deicing salts on urban soils and health status of roadside trees in the Opole Region. Environmental Toxi- cology 19:296–301. Dobson, M.C. 1991. De-icing Salt Damage to Trees and Shrubs. Forestry Commission Bulletin 101. Fintelmann, L. 1877. Über Baumpflanzungen in den Städten, deren Bedeutung, Gedeihen, Pflege und Schutz. J.U. Kern’s Verlag, Breslau. FLL. 2004. Empfehlungen für Baumpflanzungen. Teil 2: Standortvorbereitung für Neupflanzungen, Pflanzgruben und Wurzelraumwerweiterung, Bauweisen und Substrate. Forschungsgesellschaft Landschaftsentwicklung Land- schaftsbau e.V. Gilbertson, P., and A.D. Bradshaw. 1985. Tree survival in cities: The extent and nature of the problem. Arboricul- tural Journal 9:131–142. Hampel, C. 1893. Stadtbäume—Anleitung zum Pflanzen und Pflegen der Bäume in Städten, Vororten und auf Land- straßen. Verlag von Paul Parey, Berlin. Harris, J.R., N.L. Bassuk, and S.D. Day. 1994. Plant estab- lishment and root growth, pp. 16–23. In Watson, G. W. and D. Neely, Eds. The Landscape Below Ground. Inter- national Society of Arboriculture, Savoy. Hillel, D. 1998. Environmental Soil Physics. Academic Press, San Diego. Holstener-Jørgensen, H. 1958/59. Investigation on Root Sys- tems of Oak, Beach, and Norway Spruce on Groundwater affected Moraine Soils with a Contribution to Elucidation of Evapotranspiration of Stands. Forstlige Forsögsväsen i Danmark, Bd. 25, S. 225–290. Kristoffersen, P. 1998. Designing urban pavement subbases to support trees. Journal of Arboriculture 24:121–126. ———. 1999. Growing trees in road foundations. Arboricul- tural Journal 23:57–76. ©2007 International Society of Arboriculture
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