Arboriculture & Urban Forestry 34(3): May 2008 Arboriculture & Urban Forestry 2008. 34(3):179–183. 179 Comparison of Methods to Reduce Sidewalk Damage from Tree Roots E. Thomas Smiley Abstract. Tree roots growing under sidewalks are known to crack or lift pavement often creating a tripping hazard for pedestrians. This experiment was conducted to determine the long-term effects of below- and alongside-pavement treatments on tree root development and sidewalk damage. London, U.K. plane trees (Platanus × acerifolia) were planted next to sidewalks at the Bartlett Tree Research Laboratory in Charlotte, North Carolina, U.S., in 1996. Treatments installed at the time of planting were: DeepRoot Universal Tree Root Barrier (UB18-2), vertical polyethylene sheet, gravel, Foamular 150 extruded polystyrene, and a structural soil. The sidewalks and soil beneath them were removed in 2006. Minimal sidewalk lifting or cracking was associated with the DeepRoot barrier, gravel, and foam treatments. Vertical root barriers and foam resulted in fewer and deeper roots under the pavement. Treatments had no impact on tree diameter growth. Key Words. DeepRoot barriers; Foamular; infrastructure damage; root barriers; sidewalk lifting; structural soil; Styrofoam; tripping hazard. Tree roots growing under sidewalks are known to cause cracking or lifting of the pavement (D’Amato et al. 2002; Costello and Jones 2003), which may create a tripping hazard for pedestrians. The cost of repairing this type of damage is in excess of $100 million per year in the United States (McPherson and Peper 1995; McPherson 2000). Vertical barriers have been tested to assess their ability to direct root growth to deeper levels in the soil, thus reducing damage to the sidewalk (Wagar and Barker 1983; Wagar 1985; Barker and Peper 1995; Gilman, 1996; Costello et al. 1997; Gilman 2006). These products tend to work better in well- drained soils than in poorly drained soils (Gilman 2006). There are also differences among root barriers in their degree of initial effectiveness (Smiley 2005; Gilman 2006). Root barriers do not tend to reduce the stability of trees planted near them and may actually increase stability by promoting deeper root development (Smiley et al. 2000). Gravel applied under pavement during construction has also been shown to reduce root growth immediately below the pavement on well-drained sites (Kopinga 1994; Gilman 2006). This is the result of the large pores in gravel, which, when installed in a well-drained site, do not retain water or nutrients needed for root growth. Structural soils are installed beneath pavement to allow for root growth while bearing the weight of the pavement and ve- hicles (Grabosky and Bassuk 1996; Smiley et al. 2006). These gravel/soil mixes allow for initial rapid root growth. The effect of this root growth on pavement longevity is not well docu- mented. It is recommended that structural soils be installed in layers totaling at least 60 cm (24 in) deep. In practice, it is common to see installations of 10 to 15 cm (4 to 6 in) beneath pavement (pers. obs.). Foamular (Owens Corning, Toledo, OH, U.S.) is an extruded polystyrene foam board similar to Styrofoam (Dow Chemical Co., Midland, MI) commonly used for building insulation. Sheets of foam are installed on the perimeter of basements and under foundations to reduce heat loss. Polyurethane foam sprays have been used to reduce root damage to replacement sidewalks (Costello and Jones 2003). The use of foam as a preventive under pavement treatment has not been documented. The purpose of this experiment was to determine the long- term effects of below- and alongside-pavement treatments on the growth of tree roots and sidewalk damage. MATERIALS AND METHODS Two sections of sidewalk were installed at the Bartlett Tree Research Laboratory in Charlotte, North Carolina, with London plane trees (Platanus × acerifolia) planted closely alongside (Figure 1). Thirty London plane trees were planted in four rows in the native Cecil sandy clay loam (CeB2, thermic typic hap- ludults) on 2 February 1996. The trees were 4 cm (1.6 in) caliper and transplanted with a tree spade on 6 m (19.8 ft) spacing. Tree trunks were centered 50 cm (20 in) from the edge of the sidewalk pavement. To install the sidewalks, soil was removed to a depth of 10 cm (4 in) from two areas measuring 1.2 m (3.96 ft) wide by 45 m (148.5 ft) long. In areas to receive underpavement treatments, an additional 10 cm (4 in) of soil was removed. Underpavement treatments were installed before pouring the concrete, whereas the vertical barriers were installed next to the edge of the pave- ment immediately after paving. The top edge of all vertical bar- riers were installed above grade. Treatments were as follows: 1) DeepRoot Tree Root Universal Barrier (UB 18-2; Deep- Root Partners, San Francisco CA)—an injection-molded copolymer polypropylene panel that is 2.032 mm (0.081 in) thick by 45 cm (18 in). Panels were installed vertically within 3 cm (1.2 in) of the edge of the pavement. 2) Polyethylene sheet (Poly sheet)—0.15 mm (0.01 in) thick by 45 cm (18 in) black polyethylene sheet was installed vertically within 3 cm (1.2 in) of the edge of the pavement. 3) Gravel—2.5 to 3.75 cm (1 to 1.5 in) diameter washed, crushed gravel was installed in a 10 cm (4 in) horizontal layer beneath the pavement. ©2008 International Society of Arboriculture
May 2008
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