Compartmentalization of Decay in Trees - Process

Process

According to CODIT, when a tree is wounded cells undergo changes to form "walls" around the wound, slowing or preventing the spread of disease and decay to the rest of the tree.

• Wall 1. The first wall is formed by plugging up normally porous vascular tissue above and below the wound. This tissue runs up and down the length of the stem, so plugging it slows the vertical spread of decay. Tissues are plugged in various ways, such as with tylosis. This wall is the weakest.

• Wall 2. The second wall is formed by the cells of the growth ring interior to the wound, thus slowing the inward spread of decay. This wall is the second weakest, and is continuous except where intersected by ray cells (see next section).

• Wall 3. The third wall is formed by ray cells, which are groups of cells oriented perpendicularly to the stem axis, dividing the stem into sections not entirely unlike the slices of a pie. These groups of cells are not continuous and vary in length, height and thickness, forming a maze-like barrier to lateral growth of decay. After wounding, some ray cells are also altered chemically, becoming poisonous to some microorganisms. This is the strongest wall at the time of wounding, prior to the growth of the fourth wall.

• Wall 4. The fourth wall is created by new growth on the exterior of the tree, isolating tissue present at the time of infection from that which will grow after. This is the strongest wall, and often the only one which will completely halt the spread of infection. When only the fourth wall remains intact, the result is something most people have seen walking through the woods or in a park: a living tree with a completely rotted-out interior. In such cases, all the tissue present at the time of injury has become infected, but new healthy tissue has been allowed to continue to grow outside of the fourth wall.