Tree root-soil interaction: field study of the effect of trees on soil moisture and ground movement in an urban environment

Abstract Aims Little research has been conducted to quantify the atmosphere-plant-soil interaction in urban environments due to a lack of understanding of plant water use characteristics and the limited availability of high-quality field data. This research aims to quantify the drying effect of root systems of two Australian native tree species on soil water dynamics and ground movement using high-quality field measurement data. Methods A long-term field monitoring on soil moisture variation and ground movement close to C. maculata and M. styphelioides, was conducted for up to 45 months in Melbourne, Australia. The water requirement of each tree was monitored using sap flow sensors. Laboratory soil testing was conducted to obtain soil properties and develop profiles of soil suction and water content. The intercorrelation between soil water dynamics and tree soil water use was established. Results Tree roots could no longer extract water from the soil when total soil suction exceeded a wilting point of approximately 1000 kPa. The soil profile differences between the two sites were a significant factor causing substantial differences in tree water consumption. Conclusions At the C. maculata site, tree-induced soil desiccation occurred to a depth of 1.1 m, while at the M. styphelioides site, it extended down to 2.2 m depth. The tree root-soil interaction analysis shows that water uptake of 10.64 kL by tree roots partially contributes to a 5% decline in soil water content and a 270 kPa rise in soil suction, resulting in a continuous soil settlement of 22 mm.