Estimation of root bundle model with Weibull survival function parameters for lateral roots of Cryptomeria japonica (L.f.) D. Don and Chamaecyparis obtusa (Siebold et Zucc.) Endl. 5 years after felling by thinning and determination of their application to the estimation of soil reinforcement by roots

Abstract

Estimation of soil reinforcement (SR) by lateral roots in sugi and hinoki plantations after thinning using root bundle model with Weibull survival function (RBMw) necessitates determining and adding SR by roots of thinned trees to that of live trees. RBMw parameters were estimated from pullout tests on 5-year-old thinned tree roots and decay coefficients representing temporal change in SR by roots post-thinning were obtained. SR by roots, estimated by applying RBMw to the horizontal root distribution data obtained from 38-year-old sugi and 53-year-old hinoki forests 6 years post-thinning, was 10.9 and 12.5 kN/m² in thinned and unthinned sugi forests, and 5.9 and 6.0 kN/m² in thinned and unthinned hinoki forests, respectively. SR by decayed roots in thinned forests accounted for only 0.9 and 3.4% in sugi and hinoki forests, respectively.