What is Cladoptosis?
by Board Certified Master Arborist Mitch Hoy
Cladoptosis is the process by which trees alter their canopies by the purposeful die-back and shedding of branches. It is a mechanism that trees have to optimize their own anatomy and structure.
The reasons for cladoptosis to occur can be numerous and very species dependent. Cladoptosis can occur any time a branch fails to achieve a net gain in carbon reserves to the total organism. Other common reasons are moisture deficiency, presence of a pest or pathogen, or soil and root compaction. Locally, we are seeing a lot of cladoptosis with the drought, paired with the early leaf abscissions we have seen in late spring.
During the process of cladoptosis, a tree forms an abscission zone by depositing resins or gums at the point of attachment of a branch, shutting off the exchange of carbohydrates and transpirational pull of water. Decay fungi are often necessary to further weaken the branch attachment to the point of shedding, which occurs outside of a zone of protection that prevents the fungi from entering into the main structure of the tree. This is a mutualism that reminds me of sharks allowing cleaner wrasses to perform dental hygiene- If these environmentally ubiquitous (and necessary) fungi colonize the inner xylem of trees they form heart rots and voids, but trees have evolved these branch protection zones to catch and seal off these infections during cladoptosis. The understanding of this mutualism and the role that fungi play in this process has directly informed modern pruning practices and Dr Alex Shigo’s CODIT model.
Most species of trees will exhibit cladoptosis, but their reasons for doing so depend heavily on their biome, ecological role in nature, and even life-stage. Trees from dense forest ecology have difficulty being stimulated to perform cladoptosis in open growing conditions, leading to greater pruning needs. Trees that evolved in open landscapes such as savannas or riparian conditions tend to utilize cladoptosis readily and may need overall less pruning to form healthy structure in urban conditions.
Sources:
Snyder, Michael. “Wood Whys: Self-Pruning Branches.” Northern Woodlands, March 2nd, 2015. https://northernwoodlands.org/articles/article/woods-whys-self-pruning-branches
Texas Plant Disease Diagnostic Lab. “Cladoptosis: An Interesting Phenomenon.” November 15th, 2013. https://plantclinic.tamu.edu/2013/11/15/cladoptosis-an-interesting-phenomenon/
Gilman, Edward. An Illustrated Guide to Pruning, Third Edition. Clifton Park NY, Delmar, Cengage Learning, 2012.
Image:
HandWiki.org
