Monday, March 27, 2017

Counting pecan wood rings

    Whenever we remove trees during an orchard thinning process, I like to stop for a minute and look at the rings in the wood. Each year pecan trees lay down a new and unique layer of wood tissue. Take a closer look at the rings of a tree and you'll discover a little bit more about how a tree grows. During the spring flush of growth, new wood tissue is created with numerous large vessel cells (large pores in the spring wood pictured above). These large vessels are needed to transport the massive amounts of water and nutrients required to build the spring flush of leaves and new shoots. As shoot growth ceases by early summer, demand for water and nutrients slows and the tree creates wood tissue with only small vessels (summer wood pictured above). Small wood vessel cells may not be able to conduct large volumes of water but their small diameter makes it easier to move water up the trunk during the dry summer months.  

  The annual growth rings within a tree's trunk also offer a historical record of past growing conditions. The wider the growth ring and better that year was for tree diameter growth. The photo above shows the growth rings I found inside a Kanza tree we recently removed during a tree thinning operation. During the years 2014-2016 we experienced excellent weather for pecan tree growth--adequate rainfall and plenty of sunshine. The Kanza tree responded to these good growing conditions by at a creating wide, healthy growth rings.
    But look at the rings laid down during the dry years of 2011-2013. Wood growth during these hot dry seasons was stunted by poor growing conditions. In addition, the number of large vessel cells within these growth rings are severely limited (a response to drought). These large vessel cells are also stained dark brown (especially the 2013 wood). When a pecan tree suffers from drought, the large vessels stop working and the tree plugs up the non-functioning cells to preserve water within the tree.
    Next time you remove a pecan tree, take a little time to read the story left behind in the growth rings. I always seem to learn something new.