164 Smiley et al.: Structural and Noncompacted Soils for Trees Comparison of Structural and Noncompacted Soils for Trees Surrounded by Pavement E. Thomas Smiley, Lisa Calfee, Bruce R. Fraedrich, and Emma J. Smiley Abstract. Trees in areas surrounded by pavement often have inhospitable rooting environments, which shorten their useful life expectancy. This trial was established to compare five different soil treatment options under pavement. Snowgoose cherry (Prunus serrulata) and Bosque lacebark elm (Ulmus parvifolia) were planted into 5.4 m3 (189 ft3 ) of medium containing compacted soil, gravel/soil mixture, Stalite, Stalite/soil mixture, or noncompacted soil and covered with con- crete. A variety of growth and health parameters were measured after 14 months. It was found that there was more trunk diameter growth with the noncompacted treatment than the Stalite and Stalite/soil treatments; more twig growth in the noncompacted and gravel/soil treatments than all others; higher relative chlorophyll rating in the noncompacted treatment than all others; and more root growth in the noncompacted treatment (elms only). Suspended pavement over noncompacted soils provided the greatest amount of tree growth and health and should be considered when designing urban planting sites for trees. Key Words. Biobarrier; Bosque lacebark elm; CU Soil; geotextile; planting pits; Prunus serrulata; skeletal soil; Snowgoose cherry; soil compaction; Stalite; structural soil; suspended pavement; suspended sidewalks; Ulmus parvifolia; urban plaza; urban tree planting. Although the benefits of trees to the urban environment are widely acknowledged, highly developed urban areas are det- rimental to the trees themselves. Many factors such as air pollution, poor drainage, and damage by people or vehicles contribute to the short life expectancy for urban trees. How- ever, the most limiting factor in the growth of urban trees is the lack of usable soil for root growth (Craul 1992). To meet this challenge, several “structural” or “skeletal soils” have been developed as alternatives to the typical com- pacted soil required to bear the weight of pavement and ve- hicular traffic in urban areas. Researchers at Cornell Univer- sity have experimented with a gravel and soil medium, con- sisting of 80% stone 20% soil (by weight) and a small amount of hydrogel to prevent the two from separating during mix- ing. Research suggests that this mixture, known as CU Soil is more beneficial to urban trees than standard compacted soil (Grabosky and Bassuk 1995; Grabosky et al. 1998; Grabosky et al. 2002). Likewise, Carolina Stalite Company (Salisbury, NC, U.S.) developed a structural soil treatment using a porous expanded slate rock known as Stalite. This material can take the place of the solid rock used in the CU Soil and provide additional water and air storage capacity when mixed with 20% sandy clay loam (Costello and Jones 2003). Stalite and gravel/soil mixtures are both capable of meeting engineering require- ments in urban areas by forming a stone matrix under the pavement. Meanwhile the soil found between the stones is noncompacted, leaving room for air exchange, water holding, ©2006 International Society of Arboriculture and root growth. Research has shown that this model encour- ages roots to penetrate deeper into the ground rather than shifting the structural soil upward and causing pavement fail- ures (Grabosky et al. 1998). Another option is suspended pavement over noncompacted soil; this construction technique allows the use of higher us- able soil volume under the pavement. The pavement may be either precast concrete lowered onto footers or concrete poured in place (Don McSween and James Urban, pers. comm.). Although structural soils only contain approximately 20% soil by volume, which may affect water and nutrient availability, suspended pavement can have nearly 100% of the soil volume in noncompacted soil. Although research has been conducted on these structural soils individually, no comparison has been made of their gravel/soil mixture, Stalite, Stalite/soil mixture, and noncom- pacted soil installed under a suspended sidewalk. This ex- perimental was developed to compare the ease of installation of each product, the impact of each treatment on tree growth, required maintenance practices, and the impact on the pave- ment over time. The results of the treatments in the first year of growth are reported in this article. MATERIALS AND METHODS Three trenches6×24m (19.8 × 79.2 ft) were completely excavated to a depth of 0.6 m (1.98 ft) at the Bartlett Tree Research Laboratory in Charlotte, North Carolina, U.S. dur- ing the spring of 2004. The trenches were lined with a thick
July 2006
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
