Cladoptosis

Self-pruning

Perhaps you’ve noticed them before while walking through a forest. Nubs or scars on the trunk of a tree where branches used to be. Your eyes train up its length to where full branches and a vibrant canopy bask in the sun. Has the tree been damaged? Is it sick or diseased?

Probably not. In fact, the tree was likely attempting to avoid harm or illness, or expend its resources in a manner more conducive to continued growth. A process called cladoptosis.

It’s a form of self-pruning or the shedding of branches that are, in most cases, either overly-shaded and no longer promoting growth, or are diseased and pose a threat to the tree. The term comes from the Greek words "clados," which refers to a branch, and "ptosis," which means falling. Essentially, falling branches.

Research into the hows and whys of the process has yielded a range of results that also depend upon the species of tree. Additionally, it may serve as a form of asexual reproduction. Or for others, a means of combating environmental conditions like drought.

But often, it results from the need to remove less vigorous or compromised foliage. That’s what we see frequently here in the temperate rainforests of the Pacific Northwest. In a dense or mature forest, branches may become too shaded to contribute enough resources. So the tree releases the attachments that are no longer enabling optimal growth.

But as previously mentioned, it’s not just letting go for the sake of growth. It is removal in the name of preventing harm. Sometimes it’s not shade, but disease that triggers the process. Regardless of the causation, to save itself from heart rot and internal voids, a tree will form an abscission zone by depositing resins or gums at or near the point of attachment of a branch, shutting off the exchange of carbohydrates and transpiration of water.

Fungi often finish the job by weakening the branch to the point of shedding. However, the tree closes itself off from potential harm by producing a zone of protection that prevents fungi or anything else that could cause damage from entering the trunk.

Self-pruning is a means of letting go of the things that no longer serve you, while preventing latent traumas on the outside from getting in. With trees, it’s called cladoptosis.