“Litter marks” around oil palm tree base indicating infiltration area of stemflow-induced water Nor Suhada Abd Rashid 1 , Muhamad Askari 2 1 Dep. of Hydraulics and Hydrology, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia. 2 Institute of Environmental and Water Resources Management, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia. Abstract The “litter marks” which has the dark color and shape like a circle was found around the oil palm tree base. These litter marks seem to be caused by the infiltration excess overland flow due to higher intensity of stemflow than the infiltration capacity of surface soil. An experiment was conducted to determine relationships between the diameter at the tree base and the radius of litter mark or infiltration area mark from the center of the stem. Result shows that the litter marks around oil palm tree base can be a useful indicator to estimate the infiltration area of stemflow- induced water. Key words: litter mark, infiltration area, oil palm tree, stemflow. 1.0 INTRODUCTION Canopies of forested and agricultural ecosystems, including oil palm trees, can significantly alter rainfall patterns into stemflow and throughfall areas. However, the effect of stemflow on the groundwater recharge is relatively large (Taniguchi et al., 1996). Previous studies have shown that stemflow can be a major source of tree-induced infiltration and subsequent flow in and below the soil root zone, including recharge (Pressland, 1976, Tanaka et al., 1996, Aboal et al., 1999, Gómez et al., 2002, Liang et al., 2007, Sansoulet et al., 2008, Liang et al., 2011). The infiltration area of the stemflow-induced water, A i was needed to determine groundwater recharge amount as a unit of water column, R s (R s = amount of stemflow/A i ). However, it is difficult to evaluate A i . Tanaka et al. (1991) evaluated A i based on the data of “infiltration area mark” which have the shape like a circle, whereas Iida et al., (2005) evaluated it based on the