Compartmentalisation of Decay in Trees (CODIT)
 

The CODIT was developed by the renowned tree expert Dr. Alex Shigo. It is a model of how trees form barriers to prevent the spread of pathogens after they have been wounded. The model consists of four parts, with each part the tree carries out a specific task creating a wall.

 
Wall 1 – resists vertical spread
 
Wall 2 – resists inward spread
 

Wall 3 – resists lateral spread
 
These three walls are created in wood present at the time of injury/infection.
 
Wall 4 – Forms a barrier zone
 
This takes place after the injury/infection; the still living cambium begins to form a boundary separating the wood present at the time of injury from the new wood that will continue to form
 
CODIT is a model representative of a trees natural ability to defend itself. Little may be understood about how the tree knows how big these boundaries should be, but creating them to defend itself from decay does require energy and therefore reduces energy reserves. This can and will lead to the formation of weak or even no boundary protection if the process is carried out repeatedly. I must stress the importance of this and we must mindful of this when pruning, etc. is being undertaken, so we do not end up with a poor defensive system.
 
To be able to help we must first understand!