Wednesday, March 14, 2018

Big native pecan tree weakened by wood rot

    Last harvest season, I came across a tree (photo at right) that I was scared to shake. From a distance it just looks like is a big old native tree that bears the scars of the 2007 ice storm (numerous sprouts from chopped-off limbs). It was only when I went to clamp onto the tree that I noticed a large crack in the trunk. I carefully shook the tree in December  but made a mental note to remove the tree come late winter.

    The trunk of this native tree had a large crack running over eight feet in length (photo at left). I looked inside the crack and discovered a rotten cavity inside the core of the tree. This tree was a potential disaster waiting to happen so I decided to cut it down.

    Cutting down a hollow tree can be tricky. The structure of the tree is so weak that you can't predict when or how the tree will fall once you start cutting. I had cut only one quarter around the trunk, when I heard the sound of wood splintering and cracking. I pulled out my chainsaw and moved away from the tree to watch it come crashing down. It was not the prettiest way to fell a tree but at least this potentially hazardous tree was on the ground (photo at right).

    The way the tree split apart upon falling allowed me to photograph the internal structure of the wood. I've labeled the key portions of the tree trunk in the photo above. Starting at the far left is a very normal looking layer of bark. Inside the bark are multiple layers of white sapwood. The heartwood of this pecan tree is reddish brown. As I looked to the center of the tree I came across a portion of the heartwood that was riddled with the white hyphae of a wood-rotting fungus. Fungal decay of the heartwood caused it to become soft and lighter in color. The hollow core of the tree represents the portion of the wood that has been completely broken down by fungal activity.    

    Inside the hollow core of the tree, I found the fruiting body of the wood-rotting fungus (photo at right). This fungus is a member of a mushroom family commonly referred to as shelf fungi. The fruiting body of this mushroom is hard and feels woody. Rather than gills, the underside of the shelf fungus has numerous pores that release spores. The appearance of shelf fungi on a tree is sure sign of significant internal wood rot.