Recent Advances in Tree Root Mapping and Assessment Using Non-destructive Testing Methods: A Focus on Ground Penetrating Radar

Abstract

This paper provides an overview of the existing literature on the subject of assessment and monitoring of tree roots and their interaction with the soil. An overview of tree root systems architecture is given, and the main issues in terms of health and stability of trees, as well as the impact of trees on the built environment, are discussed. An overview of the main destructive and non-destructive testing (NDT) methods is therefore given. The paper also highlights the lack of available research based outputs in the field of tree roots and soil interaction, as well as of the interconnectivity of tree roots with one another. Additionally, the effectiveness of non-destructive methods is demonstrated, in particular ground penetrating radar, in mapping tree root configurations and their interconnectivity. Furthermore, the paper references recent developments in estimating tree root mass density and health. Keywords: assessment of tree roots; destructive testing methods; non-destructive testing methods; ground penetrating radar (GPR); tree root interconnectivity; tree root mass density. vertical plane, they are called buttress roots, the presence of which has been associated with soils that offer poor anchorage (Henwood, 1973). Beyond the zone of rapid taper emanates a framework of woody structural roots that gather water and nutrients from long distances to the trunk: their size is often influenced by mechanical stresses such as the wind load (Stoke, 1994).  Non-woody roots: also known as fine or absorbing roots, they are responsible for the absorption of water and nutrients (Pallardy, 2008), the synthesis of rooting hormone, root exudation, and symbiosis with soil microorganisms. As the name suggests, they do not undergo secondary thickening, are generally small in diameter (<2 mm) and their lifespan ranges from days to weeks, depending on soil conditions and temperature (Pallardy, 2008). Root architecture is quite complex and varies between and within plant species (Gregory, 2006). As far as rooting depth is concerned, it is influenced not only by the tree species but also by the type and conditions of the soil (Stone & Kalisz, 1991): in fact, the downward penetration of roots can be impeded by soils that are poorly aerated or

Health assessment of trees using GPR-derived root density maps

“…To that extend, GPR is starting to gain popularity amongst foresters and tree officers as an efficient tool for estimating root patterns in a non-destructive manner [18][19][20]. In the current paper, the GPR-based root-detection framework presented in [21,22] is tested in a complete case study in a diseased urban tree within the greater London area in the United Kingdom. Concentric measurements were taken around the investigated tree, and the measured data were subjected to the processing pipeline presented in [21,22].…”

“…In the current paper, the GPR-based root-detection framework presented in [21,22] is tested in a complete case study in a diseased urban tree within the greater London area in the United Kingdom. Concentric measurements were taken around the investigated tree, and the measured data were subjected to the processing pipeline presented in [21,22]. In particular, a threestep procedure was applied.…”

A Reflectivity-Based GPR Signal Processing Methodology for Mapping Tree Root Systems of Street Trees

“…Furthermore, it is a proven and efficient method for investigating road infrastructures [19], ranging from the evaluation of pavement layer thicknesses [20,21], to damage assessment in hot-mix asphalt (HMA) layers [22], load-bearing layers and subgrade soils [23]. Finally, recent advances in the use of GPR include the assessment and monitoring of tree root systems [24][25][26].…”

Assessing the Internal Structure of Hollow Trees Using GPR and Microwave Tomography

“…Furthermore, ground-penetrating radar (GPR) has proven to be a suitable and powerful method in forestry engineering applications [18]. Recent research has shown GPR potential in tree trunks monitoring [18,19] and tree root system investigations [20][21][22][23].…”