Strength properties of wind- and snow-damaged stems of Picea sitchensis and Pinus sylvestris in comparison with undamaged trees

This study compared the strength properties of wood taken from Sitka spruce (Picea sitchensis (Bong.) Carr.) and Scots pine (Pinus sylvestris L.) tree s damaged as a result of wind and snow. The spruce trees were located in tr iplets of stems of similar diameter that had snapped, overturned (i.e., upr ooted), or remained undamaged as a result of wind and snow. The pine trees were located in pairs of similar-sized stems that had snapped or remained u ndamaged. None of the pine trees overturned. Clear wood (wood without knots and sloping grain) from the outer part of the stem of snapped Sitka spruce and Scots pine trees was less stiff (lower modulus of elasticity (MOE)) th an wood taken from the same location from overturned (spruce only) or stand ing trees. Modulus of rupture and density were unaffected. Damaged trees of both species were found to have significantly more compression wood within the test samples in comparison with undamaged trees. These findings sugges t that trees that either overturn or snap are bending more than undamaged t rees (because of their low MOE) thereby introducing a greater component of crown weight to the overall forces acting on the stem, and that this may be associated with compression wood.