Radial modulus of rupture in radiata pine measured by individual rings

New equipment was developed to measure the strength of individual annual ri ngs in green wood under predominantly tensile stress. This equipment was th en used to assess the variation of the radial modulus of rupture (rMOR) in thirty-six 25-year-old radiata pine trees taken from three sites in New Zea land. The rMOR for individual rings ranged from 3.2 to 12.7 MPa and was cal culated on the assumption that during bending of the specimens fracture was caused by the tensile force in the radial direction (i.e., perpendicular t o the tangential-longitudinal plane). No consistent trends were observed in rMOR from pith to bark; nor was there any evidence of differences between the three sites. However, there was substantial between-tree variability th at manifested mainly in different average rMOR values for the trees rather than in variations from pith to bark. These results indicate that there are no concerns with respect to splitting resistance for the juvenile wood of radiata pine. It will be of interest to investigate whether splitting resis tance is under genetic control.