Friday, August 2, 2013

Natural limb pruning: Part 2

    Last week I shared some photos illustrating how a pecan tree naturally sheds a large limb and blocks the spread of wood rotting fungi into the heart of the tree trunk. Well here's part two of that story.
    The other day I was driving our hydraulic lift back to the barn after collecting some research data. Instead of getting frustrated by the extremely slow speed this machine moves through the orchard, I lifted myself 25 feet up into the canopies of our mature trees for a bird's-eye-view.  I was now traveling through and around pecan leaves and branches gaining a fresh perspective on tree architecture and growth.  
     That's when I spotted two examples of natural limb shedding and wound healing high up into the canopy of a native pecan tree.  The first example (photo above) illustrates how the tree will eventually form callus tissue around a broken off limb in an attempt to seal off the wound. The tree can not completely grow over the wound until the remaining branch stub completely rots away or falls to the ground. Fortunately, this tree receives a strong shaking every harvest season that helps remove some of the dead wood still hanging up in the canopy.

      On the very same native tree, I found a limb wound that had healed over completely (photo at left). At some time in the past this wound probably looked a lot like the photo above. However, the dead portion of the limb has fallen away and the tree was able to callus over the wound completely. Judging from the size of the wound and the extent of callus formation it probably took 10+ years for this tree to progress from dead branch to completely sealed over wound.
    You might be wondering why I've spent so much time writing about natural limb pruning. Shouldn't I just concentrate on proper pruning techniques? Well, I'm all for making correct pruning cuts on young trees, but there comes a time when a pecan tree grows so tall that you can no longer reach high enough to trim off damaged limbs (even with my lift!).  That's when natural limb pruning along with a good trunk shaker become the only tools available for removing dead of damaged limbs from a pecan tree. And its good to know that pecan trees have developed mechanisms to deal with limb loss and can seal over old wounds.