168 Smiley et al.: Structural and Noncompacted Soils for Trees pared with close by tree lawn plantings. This sharply con- trasts the findings in this study in which twig growth in the noncompacted/suspended pavement treatment was nearly double the second best gravel/soil mix treatment in the cher- ries. With the elm, the second best twig growth rate was also found in the gravel/soil treatment and was nearly equal to the noncompacted treatment. These differences point to species variability in the response to the soil medium. Relative chlorophyll content, as measured with a SPAD meter, in a previous study (Grabosky et al. 1998) found slightly higher chlorophyll levels in field grown Acer and Malus that in a CU Soil. However, a higher chlorophyll level was found in the CU Soil treatment than field-grown Tilia. Chlorophyll levels were lower with all three species in the adjacent compacted standard sidewalk profile treatment in that study. Soil pH (8.8 to 9.1) found in the sidewalk base was thought to contribute to the lower chlorophyll content with the compacted sidewalk treatment. In this study, SPAD levels were significantly higher, meaning more chlorophyll, in the noncompacted/suspended pavement treatment than all other treatments with both tree species. Media pH (8.5) was also a factor in the Stalite treatment and to a lesser degree in the Stalite/soil treatment. The reason for the differences between the two studies in not obvious. When designing for planting in spaces that require a solid surface for vehicles and pedestrians, the option of using suspended pavement over noncompacted soil has not re- ceived much attention over the past few years. It has been used successfully in places like downtown Charlotte, North Carolina. The differences in tree growth among treatments was dramatic; trees growing in the noncompacted soil sus- pended pavement treatment are visually healthier in appear- ance and provide more shade more quickly than any of the other treatments. If suspended pavement is to be used, the pavement will need to be engineered to take expected loads without fracturing. This may require greater reinforcement than pavement installed over structural soil and installation of footers. The tree growth, maintenance requirements, and pavement damage from the trees in this plot need to be monitored for 10 years. Acknowledgments. We thank Robert Bartlett, Jr., and the F.A. Bartlett Tree Expert Co. for support of this project; James Urban, Dr. Jason Grabosky, Neil Harley, Dan Thompson, and Don McSween, for technical advice in the layout and construction of the research plot; Jerry Dunaway and Bill Hawkins of BBA Fiberweb and Chuck Fredrick and Debbie Stringer, Carolina Stalite Co., for contributing materials used in the project; Ethan Stewart, Imogene Mole, and Elden LeBrun for assistance with the construction of the plot; Dr. Donald C. Booth for insect evaluations; Dr. Christina Wells at Clemson University for assistance with data analysis; and Laura Johnson and Greg Paige for plot maintenance. ©2006 International Society of Arboriculture LITERATURE CITED Costello, L.R., and K.S. Jones. 2003. Reducing Infrastructure Damage by Tree Roots: A Compendium of Strategies. ISA Western Chapter, Cohasset, CA. Craul, P.J. 1992. Urban Soil in Landscape Design. John Wiley and Sons, New York, NY. Grabosky, J., and N. Bassuk. 1995. A new urban tree soil to safely increase rooting volumes under sidewalks. Journal of Arboriculture 21:187–201. Grabosky, J., N. Bassuk, and B.Z. Marranca. 2002. Prelimi- nary findings from measuring street tree shoot growth in two skeletal soil installations compared to tree lawn plant- ings. Journal of Arboriculture 28:106–108. Grabosky, J., N. Bassuk, L. Irwin, and H. van Es. 1998. Pilot study of structural soil materials in pavement profiles. In Watson, G. (Ed.) The Landscape Below Ground II. Inter- national Society of Arboriculture, Champaign, IL. Rolf, K. 1994. Soil compaction and loosening effects on soil physics and tree growth. In Watson, G.W. and D. Neely (Eds.). The Landscape Below Ground. International So- ciety of Arboriculture, Champaign, IL. E. Thomas Smiley, Ph.D. (corresponding author) Arboricultural Researcher Bartlett Tree Research Laboratory Adjunct Professor, Clemson University 13768 Hamilton Road Charlotte, NC 28278, U.S.
[email protected] Lisa Calfee, Ph.D. Assistant Professor Queens University Charlotte, NC, U.S. Bruce R. Fraedrich, Ph.D. Director Bartlett Tree Research Laboratory Charlotte, NC, U.S. Emma J. Smiley Research Technician Bartlett Tree Research Laboratory Charlotte, NC, U.S. Résume. Les arbres entourés de surfaces pavées ont souvent des environnements inhospitaliers pour leur enracinement, ce qui di- minue leur espérance de vie. Cet essai a été conçu pour comparer cinq options différentes de type de sol sous les milieux pavés. Ces cerisiers à fleurs japonais (Prunus serrulata) et des ormes à petites feuilles (Ulmus parvifolia) ont été plantés dans des milieux
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