The measurement of sap movement in xylem sapwood tissue using heat pulse velocity sap flow instruments has been commonly used to estimate plant transpiration. In this study, sap flow sensors (SFM1) based on the heat ratio method (HRM) were used to assess the sap flow performance of three different tree species located in the eastern suburbs of Melbourne, Australia over a 12-month period. A soil moisture budget profile featuring potential evapotranspiration and precipitation was developed to indicate soil moisture balance while the soil-plant-atmosphere continuum was examined at the study site using data obtained from different monitoring instruments. The comparison of sap flow volume for the three species clearly showed that the water demand of Corymbia maculata was the highest when compared to Melaleuca styphelioides and Lophostemon confertus and the daily sap flow volume on the north side of the tree on average was 63% greater than that of the south side. By analysing the optimal temperature and vapour pressure deficit (VPD) for transpiration for all sampled trees, it was concluded that the Melaleuca styphelioides could better cope with hotter and drier weather conditions.

Expansive soils undergo significant moisture change under prevailing climate conditions, resulting in shrinkage and swelling in dry and wet months. Such seasonal movements of expansive soils can greatly affect the serviceability and performance of lightweight structures founded on shallow footing systems. The extent of movement may be exacerbated if trees are present since large amounts of water can be absorbed by the root system of trees, leading to localized settlement due to soil shrinkage. This study established a well-instrumented site that included a row of Australian native eucalypts located in an eastern suburb of Melbourne, Australia. A tree from this row was chosen for the monitoring of soil movements, soil moisture and suction over a period of 44 months. A sap flow instrument was used to monitor the transpiration and water uptake by the tree. The results showed that noticeable shrinkage settlement occurred at a radial distance of 7.8 m from the trunk of the tree, attributable in part to the increased water demand of the tree. This study promotes a better understanding of the process of expansive soil–tree root interaction. The field data presented can assist geotechnical engineers and practitioners with footing design in the presence of trees.

The influence of trees on residential footings constructed on expansive soils has long been a concern of geotechnical engineers since the invasive tree root could exert suction forces on the soil surrounding them and extract a considerable amount of water depending on seasonality, leading to significant shrinkage settlement and the subsequent foundation failure. In this study, a Eucalypt, Corymbia maculata, planted in an expansive clay site in Melbourne, Australia, was closely monitored for 44 months to assess tree-induced soil moisture patterns and ground movement. Monthly tree water use was measured using a sap flow sensor over 12 months. The results show that the tree consumed 53 kL of water annually, with the highest water demand of 5.9 kL in December and the lowest monthly water use of 2.7 kL in June. The soil suction and moisture content profiles reveal that the desiccating effect of tree roots extended to 3 m depth, while the ground movement data shows a significant shrinkage settlement at a distance equal to half the tree height (HT). A parametric study was also carried out to examine the influence of various parameters on footing design for the effect of trees and the consequent construction cost. It was found that homeowners could save a construction cost of about 32% if the footing is built at a distance of 0.6 HT from the tree compared to the cost for a footing constructed at a distance less than or equal to 0.5 HT.