Saturday, February 27, 2016

Wood growth in a forked pecan tree

    Back when I was thinning trees out of our pecan breeding plot, I cut down a tree that four years earlier had been a forked tree. The photo at right shows the basal portion of the removed tree and you can see the tree wound left by removing the fork in the tree.
    Cutting down this tree gave me the opportunity to see how pecan wood growth is effected by a tree having two main trunks. In the photo at left the red arrows point to the centers of the two trunks that began growth back when this tree was a small sapling. The yellow arrow points to the bark inclusion that developed between the two trunks.
    Four years ago I pruned out one of the two main trunks. The bark inclusion stopped spreading and four years of solid wood grew all around the tree's circumference. 

    A bark inclusion forms between the two halves of a forked tree largely in response to wind. As wind moves the upper portion of the tree, the two halves of the tree are pulled apart, splitting open the wood.
    If you look closely at the growth rings of this tree, you will note that the rings are identical on both sides of the bark inclusion (photo above). This tells me that the growth ring was formed first then split apart later.

    It is interesting to look closely at the wood growth patterns of original two stems of this tree (photo at right). At first the two stems grew independently, each forming their own growth ring. As the two grew in diameter, the stems grafted together and developed a single, shared growth ring. However, as the tree grew taller and branched out to form a larger canopy, the wind started to pull on the two trunks taring them apart.
    If you ever see a young tree develop a forked trunk, prune the tree to a single stem as soon as possible. Once pruned, the tree will grow new growth rings over any bark inclusions that may have started to develop.