Sunday, July 28, 2013
The anatomy of natural limb pruning
While I walked back to the barn to grab a chainsaw, I though-- "why don't I take a look inside this limb to see how pecan trees naturally shed large limbs broken by storms".
I mentioned earlier that I could see a difference in bark color and texture between areas of living and dead tissues. Well, that line also shows up in the cross section of the bark. The orange arrow at the top of the photo points to a dark black line in the bark that marks the boundary between living and dead tissues. And remember those pretty white fungi? Fungal growth inside the wood leaves a series of fine black lines in unique patterns that wood-workers would recognize as a condition known as "spalting" (see yellow arrow). All the holes in the wood are the result of insect activity; wood borers at first, then a colony of ants.
However, the most important thing to see in the wood of this mostly rotten branch stub is the very prominent boundary layer (blue arrow) between healthy white wood and decaying branch. By filling all the pores in the wood with water repelling organic compounds, the tree prevents wood rotting organisms from advancing into the trunk. This plugging of the pores has stained the wood a chestnut brown in a layer about 1/4 inch wide. The outside limit of the boundary zone is marked by a fine black line indicating the limit of fungal activity.
If I had let nature take its course, the rotten portion of the branch stub would eventually fall off the tree (years from now). Only then, could the tree start to callus over the wound. However, with proper pruning the callusing process can begin immediately.