If you ever have the chance to walk in the woods after a major storm, you may amuse yourself trying to figure out why a particular tree was blown down while a nearby tree remains upright. You may see trees revealed to be rotten at the base that tipped over and took apparently healthy trees with them.
The rotten parts of a tree offer their own opportunities for contemplation of wear (insect or bird damage) and corrosion (fungal action) or even the effect of moss or lichen root penetration or freeze-thaw damage. You may see apparently healthy trees pushed to the ground almost completely intact, as major portions of their root systems were lifted out of water-saturated ground. You may see tree branches in an orchard that were broken off as a result of heavy fruits. Surely such a weather-related event presents a wonderful (if sad) opportunity to meditate on the relationship between strength and stress in structures.
Figure 1 shows two trees that have been down on my property for some time. They are covered with moss, and the damage is so far along it is impossible to know the character of the original event that brought them down.
Figure 2 shows major woodpecker damage – deep holes that created a big stress raiser.
Figures 3 and 4 show two views of “hinge” events. The water-saturated ground allowed the trees to tip over as their root balls slid out of their normal position. Figure 4 shows the root side. These were big roots, and they snapped off. Furthermore, this tree was not right in the standing water (SW) as was the case for the trees shown in Figure 3.
The red-rimmed upraised root ball happened a few years ago, and the purple-rimmed one was more recent. Note the fairly deep holes (light blue circles with Hs) at the edge of the raised root ball closer to us.
Figure 4 shows a BIG tree that tipped over in drier ground than that of Figure 3. We had some ferocious winds this past winter, but this tree was probably 80 or so years old.
And the big question is why the tree shown in Figure 5 survived, and thrived to some extent, after the major deformation damage sometime in its youth.