“Living Stumps” is presented as part of a series of educational articles for Penderites on the natural world that surrounds us.
Pender Island has been logged in the past, and when out in our many park areas one can see stumps of the trees that have been felled. Many of them, cut down when the island was logged 100 years ago, are well rotted, while others felled more recently are just starting to decay. Periodically, in and amongst the Douglas Fir stumps, you can see one stump that looks odd, such as the one shown in the image below. It is not decaying and almost appears to be alive. The top of the stump has grown over and healed in a strange mushroom-like bark cap. If you have noticed this, you may have wondered what is going on? How can a tree cut years ago still be alive? However, if you could peer into the darkness underground you would find answers, because it is all about the roots. Several species of trees produce root grafts, including Douglas Firs. Grafting happens when the root systems of two or more trees come into contact and grow together. Trees joined in such a way become, in effect, one organism. In a Douglas Fir forest, a single tree could be connected with most of its neighbours. When a tree is cut or broken off, adjacent trees treat the stump as if it were a part of themselves and will send nutrients through their connected roots.
The process starts with resin soaking into the exposed wood to prevent pathogens and decay from entering, much as a tree responds to any injury to its bark or branches. Once soaked with resin, the cambium (active growth layer just under the bark), starts to form a callus in order to heal the wound. Sometimes this goes on until the stump is fully capped. Fully capped stumps remain connected to their neighbours, and while the Douglas Fir cannot sprout a new tree from the stump like some deciduous trees, the capped stump can continue to increase in girth over the years.