Earlywood and latewood elastic properties in loblolly pine

The elastic properties of earlywood and latewood and their variability were measured in 388 specimens from six loblolly pine trees in a commercial plantation. Properties measured included longitudinal modulus of elasticity, shear modulus, specific gravity, microfibril angle and presence of compression wood. Novel testing procedures were developed to measure properties from specimens of 1 mm x 1 mm x 30 mm from earlywood or latewood. The elastic properties varied substantially circumferentially around a given ring and this variation was nearly as large as the variation across rings. The elastic properties varied by ring and height, but while the modulus of elasticity increased with height, the shear modulus decreased with height. A strong correlation was found between modulus of elasticity and shear modulus, but only at low heights and inner rings. Specific gravity and microfibril angle were the strongest predictors of elastic properties and explained 75% of the variation in modulus of elasticity for latewood. Despite being the best predictors in this study, these parameters accounted for less than half of the variability of earlywood modulus of elasticity, earlywood shear modulus and latewood shear modulus.