Arboriculture & Urban Forestry 35(1): January 2009 Arboriculture & Urban January 2009. 35(1):23–26. 23 Root Growth Near Vertical Root Barriers after Seven Years E. Thomas Smiley , Liza Wilkinson , and Bruce R. Fraedrich Abstract. Vertical root barriers are used to redirect root growth to greater depths in the soil, thus reducing damage to the side- walks. This study was conducted to examine root growth patterns near a variety of vertical root barriers. Thirty willow oaks ( Quercus phellos ) were planted in November 2000 and one of the following treatments was installed on two sides of each tree: Biobarrier, DeepRoot Universal Barrier, DeepRoot Universal Barrier with Spin Out, Tex-R, Typar Geotextile 3801, or a no-barrier control. In March 2007, the second 15-tree block was excavated to reveal the root system outside the barrier. All five root barriers significantly reduced the amount of root growth compared with the control trees. There were no differences among the products tested. Key Words. Biobarrier; copper hydroxide; DeepRoot; Geotextile; infrastructure damage, sidewalk lifting, Spin Out; Tex-R; Typar. Roots from trees growing near sidewalks are known to grow under and take advantage of cracks in pavement, often result- ing in additional cracking or lifting of the pavement (Wagar and Barker 1983; D’Amato et al. 2002; Costello and Jones 2003). A study that looked at tree-related concerns of city residents in Toledo, Ohio, found that the greatest concern of citizens was the damage done to sidewalks by tree roots (Heimlich et al. 2008). The cost of repairing sidewalk damage is in excess of $100 mil- lion per year in the United States (McPherson and Peper 1995; McPherson 2000). Vertical root barriers are one treatment that has been found to redirect root growth deeper in the soil and reduce root growth under pavement, thus reducing damage to the sidewalk (Wagar 1985; Barker and Peper 1995; Gilman 1996; Costello et al. 1997; Smiley et al. 2000; Costello and Jones 2003; Smiley 2008). These prod- ucts tend to work better in well-drained soils than in poorly drained soils (Gilman 2006). It has been determined that there are differ- ences among root barriers in their initial degree of effectiveness (Smiley 2005; Gilman 2006). Because vertical barriers are known to be effective at diverting or reducing root growth under pave- ment, numerous products are commercially available (Peper and Barker 1994). This study was conducted to determine if there are root growth differences among a number of root barrier products. MATERIALS AND METHODS Two rows of 15 willow oak ( Quercus phellos ), 4 cm (1.5 in) cali- per, were planted on a 3 m (10 ft) spacing at the Bartlett Tree Research Laboratory in Charlotte, North Carolina, U.S., on 8 November 2000. Soil at the site is a moderately well-drained Cecile sandy clay loam (thermic typic hapludults). For installa- tion of root barriers, parallel trenches 45 cm (18 in) deep were dug on opposite sides of each row of trees at a distance of 60 cm (24 in) from the center line of the tree trunks. A 3 m (10 ft) long and 45 cm (18 in) deep section of root barrier was inserted into each trench centered on the tree. Each treatment was repli- cated ten times in two randomized blocks. Trees were irrigated and fertilized with granular Boost (24N–7P–7K) at a rate of 2.4 kg N/100 m 2 (6 lb N/1000 sq ft) at the time of planting. Irrigation was applied as needed after planting. Treatments installed on 19 December 2000 were as follows: 1. DeepRoot UB18-2 Universal Tree Root Barrier (DeepRoot Partners, San Francisco, CA). Panels are a copolymer poly- propylene 2 mm (0.08 in) thick and 45 cm (18 in) high × 61 cm (24.4 in) wide. Referred to as “DeepRoot Standard”; 2. DeepRoot UB18-2 Universal Tree Root Barrier with Spin Out, UB18-2 Barrier coated with Spin Out (Griffin L.L.C., Valdosta, GA), a copper hydroxide resin coating (6 g Cu[OH] 2 /m 2 ). Referred to as “DeepRoot Copper”; 3. Typar Geotextile 3801, a heavyweight (272 g/m 2 [8 oz/yd 2 4. Biobarrier, a medium weight (130 g/m 2 [4 oz/yd 2 ]) nonwoven polypropylene geotextile fabric (Reemay Inc., Old Hickory, TN); ]) nonwo- ven polypropylene geotextile fabric with attached nodules containing the herbicide trifluralin (17.5% A.I.) (Reemay Inc., Old Hickory, TN); 5. Tex-R Barrier, a heavyweight (415 g/m 2 [12.5 oz/yd 2 ) (Texel, St. Elzear, Beauce ]) needle punched nonwoven polypropylene/polyester coated with Spin Out (6 g Cu [OH]2 /m 2 Nord, Quebec, Canada). Referred to as “TexR Cu Geotex”; and 6. No-barrier control treatment. One block of 30 root barriers (15 trees) was excavated on 26 February 2002 (Smiley 2005) and a second block was excavated on 26 March 2007 for this study. Soil was excavated to reveal the root system at and beyond the barrier using methods similar to Gilman (1996). Excavations were made with a track hoe, which excavated the area between 90 cm (36 in) and 215 cm (86 in) from the tree trunk parallel to the line of root barriers. Additional soil was sliced off the side of the trench with a square-tipped shovel or was removed with an Air-Spade (Concept Engineering Group, Pittsburgh, PA). Root growth was quantified adjacent to the outside of the barrier or at the barrier line for the controls and along a parallel line 15 cm (6 in) outside the barriers. Roots were classified by diameter, either greater or less than 10 mm (0.4 in) diameter, and counted at each line at 15 cm (6 in) depth intervals. Data were analyzed using SPSS (SPSS Inc., Chicago, IL) analysis of variance to compare differences among treatments. ©2009 International Society of Arboriculture
January 2009
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