Influence of Tree Roots on Matric Suction and Soil Moisture Dynamics in Tropical Residual Soil Slopes

Abstract This article investigates active root tree zones on tropical residual soil slopes, specifically focusing on matric suction resulting from tree water uptake. Fieldwork involved collecting matric suction data with and without a mature tree (Alstonia Angustiloba) at the slope's top. The study examines how matric suction values and profiles respond to tree water intake and rainfall, revealing higher matric suction levels near the tree, significantly influenced by climate change, especially at the slope's surface. Prolonged extreme rainfall decreases matric suction, with most changes occurring within 4.4 m of tree trunks and at shallow depths (0.25 m). The findings suggest that preserving mature trees can enhance soil quality, particularly on slopes. Utilizing the unsaturated flow equation, this research confirms that tree transpiration induces suction in the unsaturated soil beneath the tree. Numerical simulations were conducted to compare soil moisture patterns with suction data from Pahang Matriculation College (PMC). Field equipment, including tensiometers, gypsum blocks, and rain gauges, recorded daily soil matric and rainfall from May 21 to June 12, 2019. The numerical model successfully simulated moisture transport patterns in the unsaturated zone near the mature tree, yielding satisfactory results. A comparison of actual soil suction patterns with simulated data indicated less than 5% variation, with discrepancies attributed to root density inconsistencies. This study highlights the critical role of trees in maintaining soil stability and moisture distribution.