Differences in maximum resistive bending moments of Pinus radiata trees grown on a range of soil types

Abstract

The maximum resistive bending moments ( M b) were measured for 164 Radiata pine ( Pinus radiata D. Don) trees spanning a range of sizes and growing on six different New Zealand soil types. M b was significantly and positively correlated with tree height, diameter at 1.4 m (DBH) and stem volume with the latter explaining the greatest proportion of the variation in M b ( R 2=0.854). Trees with higher taper (lower ratio of tree height to DBH) had higher maximum resistive bending moments than trees with low taper. Both root plate diameter and root plate depth were significantly and positively associated with M b. For trees which failed by uprooting, stem volume, height:DBH ratio and root plate width explain over 91% of the variation in M b. Differences in M b were also found between soil types. Trees growing on northern yellow-brown earths and southern yellow-grey earths had significantly greater values of M b than those growing on yellow-brown pumice soils. A higher incidence of stem failure was also recorded on yellow-grey and yellow-brown earths. This type of failure could not be successfully modelled using elementary beam theory because of the breakdown of the uniform stress assumption and the presence of stem defects.