A Root Pull-out Test for Evergreen Broad-leaved Trees in a Coastal Forest Located on a Pebble Beach

Abstract

We conducted a root pull-out test using wind-fallen Cinnamomum camphora and Morella rubra trees located on a pebble beach. The effects of root diameter and sand-pebble particle size composition on the pull-out resistance were examined. The root pull-out resistance (kN) was expressed as a power function of the root basal diameter (mm). The sand-pebble particle size composition at the locations of 14 trees subjected to the test was classified into two types by cluster analysis. The root pull-out resistance had lower values at locations with a higher proportion of pebbles sized ＞5.6 mm. There was no difference between the two species in root pull-out resistance or in root tensile strength. The parameter in the power function of root diameter and pull-out resistance in this study was smaller than those observed in previous studies conducted in a montane forest and a sand beach. This suggests a smaller pull-out resistance of tree root in coastal forests on pebble beaches with rounded gravel than in other terrains.