150 Research Note Research Note ROOT GROWTH NEAR VERTICAL ROOT BARRIERS By E. Thomas Smiley Roots from trees near sidewalks are known to grow under and take advantage of cracks in pavement, resulting in additional cracking or lifting of the pavement (D’Amato et al. 2002). The cost of the damage is in excess of $100 million 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 to lower levels of the soil, thus reducing damage to the sidewalk (Wagar 1985; Barker and Peper 1995; Gilman 1996; Costello et al. 1997). Since vertical barriers are known to divert or reduce root growth, numerous products are now available. This study was developed to examine root growth patterns near a variety of vertical root barriers. MATERIALS AND METHODS Two rows of 15 willow oak (Quercus phellos) each, 4 cm (1.5 in.) caliper, were planted on 3 m (10 ft) spacing at the Bartlett Tree Research Lab in Charlotte, North Carolina, U.S., on November 8, 2000. Soil was a Cecile clay loam. Parallel trenches 45 cm (18 in.) deep were dug on opposite sides of each row of trees, at a distance of 60 cm (2 ft) from the centerline of the tree trunks, for installation of root barriers. 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 replicated ten times in a randomized block design. Trees were irrigated and fertilized with granular Boost (24-7-7) at the rate of 2.4 kg N/100 m2 (6 lb N/1,000 ft2 ) at the time of planting. Irrigation was applied as needed after planting. Treatments were installed on December 19, 2000, as follows: 1. DeepRoot Tree Root Barrier, UB18-2 Universal Barrier (Deep Root Partners, San Francisco, CA). Panels are a copolymer polypropylene 2 mm (0.08 in.) thick and are 45 cm (18 in.) high by 61 cm (24 in.) wide. 3. Typar® Geotextile 3801, a heavyweight (272 g/m2 oz/yd2 4. Biobarrier®, a medium weight (130 g/m2 2. DeepRoot Tree Root Barrier with Spin Out®, UB18-2 Universal Barrier coated with Spin Out® (Griffin LLC, Valdosta, GA), a copper hydroxide resin coating (6 g Cu[OH]2 /m2 ). [8 ]), nonwoven polypropylene geotextile fabric (Reemay Inc., Old Hickory, TN). [4 oz/yd2 ]), nonwoven 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/m2 yd2 [12.5 oz/ ]), needle-punched, nonwoven polypropylene/ ©2005 International Society of Arboriculture polyester coated with Spin Out® (6 g Cu[OH]2 /m2) (Texel, St. Elzear, Beauce Nord, QC). 6. No barrier—control treatment. On February 26, 2002, five trees in each treatment (one block) were excavated to reveal the root system using methods similar to Gilman (1996). Excavations were made with a track hoe, by digging the area between 90 cm (36 in.) and 215 cm (84 in.) from the tree trunk (Figure 1). An additional 15 cm (6 in.) of soil was sliced off the side of the trench with a square tipped shovel to cleanly cut roots in that plane. Soil was then removed using 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. The barriers were then removed and soil was removed using an Air Spade. Roots present in the original 10 cm (4 in.) wide trench inside the barrier were pruned, dried, and weighed. Maximum root spread and number of roots on the inside of the barrier, adjacent to and parallel to the barrier, and at the edge of the original trench were measured for each treatment. The remaining trees will be excavated in the future and evalu- ated in a similar manner. Data were analyzed using SPSS (SPSS Inc., Chicago, IL) ANOVA to compare differences among treatments. Student- Newman-Keuls procedure was used for separation of means at the P = 0.05 confidence level. Figure 1. Graphic representation of root excavation process.
May 2005
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