CODIT
Encyclopedia
Compartmentalization Of Decay In Trees (CODIT) is a concept created by Dr. Alex Shigo
Alex Shigo
Alex L. Shigo was a plant pathologist with the United States Forest Service whose studies of tree decay resulted in many improvements to standard arboricultural practices. He travelled and lectured widely to promote understanding of tree biology among arborists and foresters...

 after years of studying tree decay patterns. Though disputed upon its introduction in the late 1970s, the concept is now widely accepted and can be found in many arboriculture
Arboriculture
Arboriculture is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants. It is both a practice and a science....

 textbooks.

Theoretical background

In keeping with the theory of abiogenesis
Abiogenesis
Abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose...

, in which living things can develop from non-living things, scientists traditionally believed that tree decay led to fungal growth. With the advent of germ theory, however, German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 forester
Forester
250px|thumb|right|Foresters of [[Southern University of Chile|UACh]] in the [[Valdivian forest]]s of San Pablo de Tregua, ChileA forester is a person who practices forestry, the science, art, and profession of managing forests. Foresters engage in a broad range of activities including timber...

 Robert Hartig
Robert Hartig
Robert Hartig was a German forestry scientist and mycologist...

 in the early 20th century theorized the opposite was the case, and developed a new model for tree decay: when trees are wounded, fungi infect the wounds, and the result is decayed wood. Over time, the research of Shigo and others helped to expand this theory, leading to the modern concept of tree decay: when trees are wounded, many organisms, not just fungi, infect the wood at different times and in different ways; trees respond to these infections with both chemical and physical changes; discolored and decayed wood results, but is limited by compartmentalization.

Process

According to CODIT, when a tree is wounded cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 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
    Vascular tissue
    Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...

     above and below the wound. This tissue runs up and down the length of the stem
    Plant stem
    A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

    , so plugging it slows the vertical spread of decay. Tissues are plugged in various ways, such as with tylosis
    Tylosis (botany)
    Tylosis is the physiological process and the result of occlusion in the xylem of woody plants as response to injury or as protection from decay in heartwood....

    . 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
    Maze
    A maze is a tour puzzle in the form of a complex branching passage through which the solver must find a route. In everyday speech, both maze and labyrinth denote a complex and confusing series of pathways, but technically the maze is distinguished from the labyrinth, as the labyrinth has a single...

    -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.

Practical impact

By increasing understanding of how trees respond to decay, CODIT has had many applications. For example, arborists are frequently called upon to analyze the danger posed to people or property by a damaged or decaying tree. By knowing how decay is likely to spread, such hazard tree analyses may be more accurate, thereby preventing unnecessary tree removal, property damage, or injury. For another example, in the production of maple syrup
Maple syrup
Maple syrup is a syrup usually made from the xylem sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species such as the bigleaf maple. In cold climates, these trees store starch in their trunks and roots before the winter; the starch is then...

 holes are drilled into a tree's vascular tissues, which necessarily damages the tree. CODIT has helped farmers to better understand the effects of different tapping techniques and accordingly to change their methods to minimize damage and maximize production.

Work done by Gilman et al. at the University of Florida
University of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...

shows that a wound's proximity to leaf mass greatly influences compartmentalization as well as wound closure.
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