Wednesday, August 31, 2011

Tree age and drought stress.

    Looking over our pecan grove,  I've noticed that large, older trees handle drought much better that young trees.  To show you what I'm talking about, I photographed leaves and nuts from two trees. The first was 28-years-old and about 12 inches in diameter, while the second was 9-years-old and about 3 1/2 inches in diameter. Both trees had been grafted to Pawnee and both were bearing nuts.
    In the photo above, the leaf on the left is from the older, larger tree while the leaf on the right was pulled from the young tree. Both leaves were taken from the mid portion of this year's growth. The smaller leaves on the younger tree were also lighter green.

    I  then pulled a cluster of nuts off of each tree. The cluster on the left is from the older tree, while the smaller nuts on the right were pulled from the smaller tree. In a previous post, I mentioned that young trees often produce smaller pecans than mature trees. But this year, the effect will be exaggerated by the drought.
    The smaller leaves and nuts found on young trees is an above ground reflection of the fact that the tree has not yet developed a large enough root system to dominate its surroundings.  A tree with a limited root system has a harder time competing for water and nutrients. Less water and nitrogen means smaller, lighter green leaves and much smaller pecans at harvest.
     Have you ever wondered why young trees respond so well to weed control while older trees seem to tolerate ground cover plants growing right up to the trunk?. It all about becoming the dominate plant in the landscape. From my experience, pecan trees become dominate when the reach 10-12 inches in diameter.