London planetree walls off decay

Did you know that trees can build walls?  In fact, trees respond to bacterial, fungal, and other attacks by constructing four walls, first modeled by Dr. Alex Shigo and named CODIT or compartmentalization of decay in trees.

CODIT via "Tree Decay" -- Figure 15 (image source)

The first wall is formed by plugged xylem cells which prevents the vertical spread of decay while late-forming cells are plugged to create the second wall which resists the inward spread of decay.  The third wall, formed by ray cells, prevents the radial spread of decay.  Together, these three walls are known as the reaction zone.  The fourth wall, also known as the barrier zone, inhibits the outward spread of decay.  This wall is "an anatomical and a chemical wall" formed by the cambium. 

CODIT pattern via "Tree Decay" -- Figure 41 (image source)

Review more patterns of compartmentalization here.

The photographs used in this post are of a London planetree round shown during the first meeting of the Trees New York Citizen Pruner Fall 2010 course being taught by Steven Boyce of the Friends of Greenwich Street.  Stay tuned for our presentation of Boyce's paper titled "It Takes a Stewardship Village: Reducing Street Tree Mortality Rates in an NYC Neighborhood."

Citations:

• Tree Decay: An Expanded Concept, USDA Forest Service Information Bulletin Number 419, April 1979 (online)
• ISA Arborists' Certification Guide, Sharon J. Lilly, 2001