Minimum filling thickness based on characteristics of distribution of Pinus thunbergii root systems in damp, lowland sand dunes of the coastal forests

摘要

There are many damp, lowland areas in the coastal forests of Kujukuri where mass withering of black pine (Pinus thunbergii) often occurs. Therefore, the relation of DBH of black pine to T/R, and the relations of ground height to existence rate and vertical distribution of black pine root systems were examined. T/R was not influenced by the increase in stem diameter. Existence rate and vertical distribution of root systems of black pine were related to forest ground heights. The higher the elevationof the ground, the higher the survival rate, and the deeper the distribution of root systems. The vertical depths of the root systems were considered to determine the survival age of the trees, and the relations were expressed by: y=2.1X+11.6 (y: depthsof surviving roots (cm); X: tree, ages (years)). The minimum filling thickness (Ft, cm) can be determined by first determinating the expected forest age. The vertical depth of the root system necessary for survival can be calculated by the above formula. We dug up the root system of a black pine over 20 years old and growing near the filling site, and measured the vertical depth of the root system (rd:cm) and the level of the digging site (gh: cm). The necessary filling thickness (Ft, cm) is: Ft = (Rd-rd) + (gh -Gh ), where Rd(cm) is the vertical depth of the root system at the expected forest age, and Gh(cm) is the level of the filling site (cm).