Study on tree root systems volume 3

Volume III of this project report contains a study of tree root systems using ground penetration radar systems. The root system of plants is the least understood component of plant physiology and ecological studies due to the difficulty in mapping the roots. There has not been much research carried out overseas on a technology known as ground penetrating radar (GPR) for mapping tree root system without the need for excavation or other invasive techniques. The intended objectives of this study was to provide an assessment of the usefulness and limitation of GPR technology using Tree Radar Unit (TRU) equipment in generating tree root maps by comparing the TRU method with other methods of root examination. Verification results suggested that the reliability of TRU is site specific. Several factors affected the results which include soil conditions, dielectric number, and scanning grids. The reliability of TRU data based on the root number detected is 40- 75% and based on the root depth detected is 80%. TRU’s advantage over other methods like air-spading was in the short time needed to do the investigation on site. However, TRU processing sometimes takes a longer time than the time required for air-spading. Knowing the reliability of the TRU result, the choice between TRU and air-spading will depend on budgetary and site constraints. Based on the verification and TRU scanning results of limited number of trees, distribution of the roots at different site and soil conditions can be characterized. The roots that grow in the structural soil were shallower and thicker as compared to those in the in-situ and top soil as shown in the verification results at IMM site. The roots in the structural soil also preferred to grow towards certain directions whereas the roots in in-situ soil are evenly distributed. Compacted sub-grade and sub-base below the pavement and aeration slab on car-parks and roadsides caused the number of roots to decrease and grow deeper. Although the ground penetration radar method is non-intrusive and fast to conduct, problems still arise in the processing of the GPR results and therefore, more development in the GPR technology is required in order to achieve more accurate and reliable results. As the current GPR technology can only provide preliminary information on the root distribution of trees only, its contribution to the NParks tree protection zone is very minimal