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Studies of root reinforcement for soil slope stability require the knowledge of root pattern, radius of root spread and root density. In Mae Prong-Mae Pun watershed, Laplae district, Uttaradit province. The field investigation, the roots were exposed by water jetting. Then mapping of root distribution by 3D-scanner, photography were taken. Inverse Pagoda (Chedi) pattern of orchard plants and natural forest trees is the most common pattern, it is accounts 9 of 14 investigated trees found on orchard plants and natural forest tree. Then bowl and monk alms bowl pattern are the less common, they account for 3 and 2 out of 14 tree types respectively, found on pioneer plant. Natural forest tree have the largest root spread with radius of 3-5 m., then orchard plants, 0.9-3.7 m., and pioneer plant, 0.5-0.8 m., respectively. Natural forest tree also has the deepest root depth of 0.8-1.6 m., then orchard plant is 0.9-1.3 m. and pioneer plant is 0.3-0.5 m. Root density in term of Root Area Ratio (RAR%). Pioneer Plants has maximum RAR% of 2-3.2% at 0.1 m. When orchard plants and natural forest trees have RAR of 7-17% at 0.2 m. and 4-8.5% at 0.1-0.2 m. deep respectively. Coffee tree (Coffea robusta Pierre ex Froehner L.) has the advantage of preventing soil surface erosion is with thickness of fibrous root, RAR% 22-37% at 0-0.6 m. Root Cohesion can be evaluated by the root density and Root Tensile Strength in further research.
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