Tensile strength and root distribution of Acacia mangium and Macaranga tanarius at spatial variation(Case study: East-West highway, Malaysia)

Abstract

Directional distribution of roots and their tensile strength are the major factors which affects the soil shear resistance. Additional cohesion provided by roots can increase soil resistance to shallow landslide and mass movement. The aim of this study is to investigate individual root tensile strength (Tr)and whole root distribution of Acacia mangium and Macaranga tanarius in rainforest with regard to position around the tree stem.Excavation method was used for collecting roots around each tree at two distances of 25 cm and 1 meter from tree stem. The results showed that there was a significant difference between root tensile strength in two species at two distances and Tr was significantly higher for Acacia mangium (50.49± 2.31MPa at 25 cm for the root diameter range between 0.16-5.06 mm and 43.67 ± 2.44 MPa at 1 meter for the root range between 0.11-5.02 mm) than Macaranga tanarius (27.64 ± 1.72 MPa at 25 cm, root diameter range between 0.16-5.66 mm and 23.81 ± 0.97 MPa at 1 meter, the root diameter range between 0.21-6.34 mm). The results indicated that Tr was significantly higher at 25 cm than 1 meter at both species. Root area ratio (RAR) results showed that there was no significant difference in RAR at 25 cm and 1 meter of the stem in Acacia mangium, but that value showed a significant different in Macaranga tanarius at 25 cm and 1 meter. Root tensile strength and RAR are the key matters for understanding additional cohesion by plant roots. In order to assess soil reinforcement by vegetation roots, root tensile strength and RAR data in different vegetation and different sites are necessary.