One of the more unpleasant parts of my work is condemning elderly trees. Redwood and oaks in our region can live for centuries, but none last forever. It is sometimes my job to determine if some of the oldest of oaks have deteriorated to such an extent that they have become unsalvageably dangerous to those around them.
What is worse than that is that there are so many dangerously deteriorated oaks and other trees that collapse before they get removed, and many do so before anyone notices how dangerous they are. Some structural deficiencies and instabilities are concealed to the most thorough of arborists. That is what happened with this big coast live oak, Quercus agrifolia, with a five foot wide trunk, that fell behind Felton Presbyterian Church. I had known for some time that the healthy canopy was heavy and exposed to wind. What I did not know is that the root systems was insufficient to maintain stability when strong wind blew against the healthy canopy while the soil was saturated. The insufficiency of the root system became apparent not only because the tree destabilized, but also because the minimal root system became exposed by the destabilization. There was no evidence of decay or damage within the root system, which are what typically contributes to destabilization.
1. It is amazing that this tree stood for as long as it did with such minimal roots.
2. This is what those minimal roots supported for so long.
3. Healthy foliar growth on top of the canopy enhanced weight and wind resistance.
4. Damage was surprisingly minimal.
5. This decay within one of the main limbs was a structural deficiency that did not contribute to the destabilization.
6. (above) This is the same picture as #5. The red line is at the cross section of where a limb broke or was cut away many years or decades ago. Although the straightness of the zone suggest that it was made by a pruning cut, it is unlikely that the tree was pruned up as high as this section of limb was located, particularly so long ago. As the tree compartmentalized the wound, decay spread inward toward the center from the wound, in a typical pattern that resembles a section of a pie chart, which is marked by the yellow lines. Once it reached the center, decay radiated outward from the center, in a typical circular patter, which is marked by the blue circle. As the center of the trunk rotted and deteriorated, the necrotic zone between it at the original wound continued to rot and deteriorate. By that time this cavity developed, the exterior of the wound had already been compartmentalized by viable wood that did not decay.
This is the link for Six on Saturday, for anyone else who would like to participate: