Scaling the Roots Mechanical Reinforcement in Plantation of Cunninghamia R. Br in Southwest China

Alam Mehtab,Jia-Jia Li,Sadiq Shamsher,Li-Jun Su,Yuan-Jun Jiang,Rahman Mahfuzur

doi:10.3390/f12010033

Abstract

The degree of mechanical reinforcement provided by plants depends upon its roots distribution in the soil and mechanical properties of the roots. The mechanical properties and distribution of root traits (root diameter and number) in the soil of the standing forest depends on the tree stem diameter. This variation of root traits with tree stem diameter is rarely investigated. Therefore, this research presents the effect of tree stem diameter on the distribution of roots within the standing forest of Cunninghamia in the Longchi forest area, Sichuan province, China. In this area, shallow landslides take place frequently. We investigated the root traits distribution for trees with different stem diameters, i.e., 220 mm, 320 mm, 450 mm, and 468 mm, to show the variation of roots distribution in the soil with stem diameter. The root architecture of the selected trees was studied by step excavation method of the root zone accompanied by measurement of roots physical parameters (roots number and roots diameter) and indices (roots area ratio (RAR), roots biomass (RB), and roots distribution (RD)). We measured the root’s maximum tensile strength by performing root tensile tests in the laboratory. The field and laboratory-measured data were used to estimate the root cohesion by both the commonly used model Wu and Waldron Model (WWM) and Fiber Bundle Model (FBM). The results indicate that the tree stem diameter correlates with both the root distribution and the tensile strength. The roots indices and root cohesion increase with an increase in the diameter of the tree. Further, RAR decreases with depth and lateral distance from the tree stem, while the maximum values were observed in 10 cm depth. The relationship between roots diameter and roots tensile strength is established through power function. The average root cohesion estimated for a tree with stem diameter 220 mm is 23 kPa, 29 kPa for 320 mm, 54 kPa for 450 mm, and 63 kPa for 460 mm. This effect of stem diameter on the increase of soil shear resistance should be considered while evaluating the stability of slopes in standing forests. The comparison between WWM and FBM for investigated species suggests that WWM estimates the cohesion values greater than FBM by 65%.

Highlights

Introduction ditions of the Creative CommonsAt-The control of geological hazards, soil erosion and slope instability, always remained challenging in hilly slopes
The study through the field investigation reveals that the root architecture of the inThe study through the field investigation reveals that the root architecture of the vestigated species is the VH type
We have demonstrated the role of stem diameter in providing root cohestudy, we have thelaboratory role of stem diameter in providingstatistical root cosion In to this the soil through fielddemonstrated investigations, testing, and performing hesion to the soil through field investigations, laboratory testing, and performing analysis

Summary

Introduction

Introduction ditions of the Creative CommonsAt-The control of geological hazards, soil erosion and slope instability, always remained challenging in hilly slopes. Sendai Framework for Disaster Risk Reduction and the Sustainable Development Goals (SDGs) [2,3]. The prevention of these geological disasters through conventional structures, which are steel, or concrete made, are mostly uneconomical and have an adverse effect on the environment. Because of these reasons, the soil bio-engineering measures, which are economically sustainable, are gaining popularity as a remedial measure for control of soil erosion and landslides preventions. This enhancement of soil mechanical properties by roots depends on roots tensile strength, soil–

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