Friday, May 27, 2011

Anatomy of a narrow branch angle

   Whenever I talk about pruning pecan trees, I mention the importance of avoiding narrow angled branches. The photo at right is an example of  pecan branches that have formed a narrow angle. Note the bark crevice where the two branches come together and the ridge of bark that extends down from the narrow angled crotch. After cutting these branches out of a tree with a chain saw, I was able to break these branches apart just like breaking a turkey wishbone.
     In the photo below, you can see why narrow angled branch connections are so weak. First, look at the bark that surrounds the exposed wood. Note that at the top of the branch connection, the bark is grey, the same color as the outside of  the branches. This was the area of the bark crevice we saw in the photo above. Along the sides of the exposed wood, the bark is tan indicating the portion of the bark that was split open when I broke apart the limbs.

    Extending downward from the bark crevice and into the wood is a dark area known as a bark inclusion. Bark develops inside the narrow angled branch connection in response to the opening between the branches (the bark crevice). Once a bark inclusion becomes well established, the only wood fibers that hold these branches together are long grain fibers found on sides of the branch connection.  Long grain fibers split apart easily, just like splitting firewood.
    Some pecan cultivars tend to produce more narrow angled branches that others. Removing stalked buds during young tree training can minimize problems associated with bark inclusions.