Arboriculture & Urban Forestry 41(5): September 2015 Arboriculture & Urban Forestry 2015. 41(5): 245–259 245 The Use of Ground-Penetrating Radar to Locate Tree Roots G.M. Moore and C.M. Ryder Abstract. Until recently the only way to investigate tree root architecture and distribution involved the physi- cal many other industries for about 30 years, has been used to study tree roots. GPR is relatively new to Aus- tralia removal and the soil. However, aim of this research past was decade, to assess ground-penetrating its spatial accuracy radar (GPR), which and ability to detect tree roots. Three experiments were conducted using a 900 MHz GPR device (Tree Radar®). The first experiment tested the ability of GPR to detect roots of sizes 10 mm, 20 mm, and 40 mm in diameter at depths of 200 mm, 400 mm, and 800 mm, while the second experiment tested its capacity to resolve two roots placed close together. Roots of 20–30 mm in diameter were placed in pairs at 20 mm, 40 mm, and 80 mm apart at depths of 200 mm, 400 mm, and 800 mm. The final experi- ment used GPR to analyze the in situ root system of a small Pistacia chinensis (Chinese pistachio) aſter which the root system was excavated using an AirSpade® and counts of root numbers were undertaken and compared with the predicted results. GPR detected and discriminated tree roots accurately at 200 mm depth, but as the depth increased to 400 mm and then to 800 mm, the levels of error increased, probably due to the choice of antenna available for the experiments, lead- ing to the presence of phantom roots in some results and the misdetection of true roots in others. Confounding of the signal with unexpected interference or inadequate signal processing was most likely the cause. ment, GPR missed many small roots in the trenches close to the tree and appeared to detect multiple roots as one. In the final experi- In the outer trenches, GPR predicted 52 roots in total but excavation revealed only one in these disturbed urban soils. Key Words. Discriminating Roots; Ground-Penetrating Radar; Root Architecture; Root Detection; Tree Radar; Tree Roots. of in the has been used in Trees can cause damage to built and hard structures. Between 1988 and 1992, tree-induced subsidence damage to buildings in the United Kingdom exceeded GBP £1.6 billion (Lawson and O’Callaghan 1995), while in the United States of America, a survey of cities estimated that annual concrete and sewer-line repair bills due to tree-related damage amounted to USD $4.28 per tree, which constituted approximately 25% of the annual tree budgets for the cities (Coder 1998). Much of the damage attributed to trees, may be the result of poor workmanship and faulty services installation (Cutler 1995; Ståhl and Rolf 1998), but tree root growth is considered by many local government managers to be an expensive nui- sance and a significant liability risk (Coder 1998). Orientation of the structural roots of a tree and inspection of the root crown have provided indi- cations of where the roots may be (Harris et al. 1999). However, in the past, the roots have had to be excavated manually using digging equipment and/or archaeological techniques (Melhuish 1968). Physical removal of soil was the only way to accu- rately map tree roots, making tree root investiga- tion costly, labor intensive, time-consuming, and oſten, if not always, destructive of the roots being investigated. Other options for investigation have included using high-pressure water or air (Air- Spade®) to blast the rooting area free from soil. For trees growing in urban situations, most of the roots are close to the surface, and if the soil is com- pacted, the roots will tend to remain near the surface (Craul 1992). Even where soils are not compacted, studies have shown that the bulk of tree roots are usually found in the top 500–1000 mm of soil (Havis 1938; Hitchmough 1994; Watson 1995; Akinnifesi et al. 1999; Peter and Lehmann 2000; Sydnor et al. ©2015 International Society of Arboriculture
September 2015
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