Decay of Trees,Alex Shigo

COMPARTMENTALIZATION OF DECAY IN TREES

Forest Service U.S. Department of Agriculture

Agriculture Information Bulletin No . 405 July 1977

Watercolor illustrations by David M. Carroll, Warner, New Hampshire.

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COMPARTMENTALIZATION OF DECAY IN TREES Alex L. Shiga Plant Pathologist, U,S, Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, Durham, New Hampshire

and Harold G, Marx Research Applications Staff Assistant, U,S, Department of Agriculture, Forest Service, Washington, D,C,

Agriculture Information Forest Service U.S. Department of Agriculture

Bulletin No. 405 July 1977

INTRODUCTION

report must be studied very carefu lly. The system is called CODIT The science of tree pathology Compartmentalization Of Decay emerged from studies on decay In Trees almost a century ago. Many of When the system is learned , it the concepts developed then will act as the code for underhave changed little over the standing a wide variety of years. But, in the last few decades some additional information defects on most tree species. on the decay process in trees The CODIT system is based on ha s been developed. Th is new two major points. First, a tree is information has added to the a hi ghly compartmented plant basic story of decay without Second, after a tree is wounded , subtract ing anything important the resulting defects are compartmentalized . from it The new expanded To apply the CODIT system concept of decay is simply more complete. And this new, more it is necessary to understand that complete concept gives us a the new expanded decay concept developed in the last few decades better opportunity to regulate and control decay. includes: 1) Successions of Dr. George H. Hepting made microorganisms associated with discoloration and decay, and 2) th e first sound observations on compartmentalization of decay in Compartmentalization of dis· colored and decayed wood tree s in 1935. His idea s acted as a trigger for the work that associated with trunk wounds. To begi n with , decay of wood followed. The work presented is a natural process caused by here is an ex pansion of hi s microorganisms, mainly fun gi, ideas. The informati on in this pubthat enter trees throu gh wounds. Tree wounds are usually inflicted lication is based on 16 yea rs of by fire, weather, in sects, birds, research by Dr. Shiga th at insmall or large animals, or man volved complete dissections of and hi s act ivities. These wounds approximately 10,000 trees start the processes that can lead mostly deciduous hardwoods, at to decay, and decay is a major least 1,000 conifers, and 17 cause of damage to trees. While tropical species. Details of these wood decay is most often caused stUdies have been published by decay-ca usin g fungi, these elsewhere. fungi are often intimately asso· The purpose of this publication ciated with bacteria and nonis to show how most columns of decay fun gi in t he process. discolored and decayed wood Decay is the breakdown or deassociated with trunk wounds in composition of dead organic trees are compartmentalized . A matter. It is also essential to great number of confusing new life. terms are given to a wide variety of defects caused by discoloraTo understand how trees react tions and decays in trees. This to wounding and the associated book describes a system that defects by compartmentalizing makes it possible for forest the defects, it is necessary to managers to understand how reevaluate our concept of how most of these defects develop. a tree is constructed. A tree is To understand the system, the considered here as a highly

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compartmented plant In a sense, a tree is made up of many trees; each growth ring is a "t ree. " Each " tree" is divided into many compartments. A compartment can be thought of as a "room," with side walls made up of rays and front and back wa ll s made up of cells that are the last to form in each growth ring. The top and bottom of the compartment is formed after wounding when the elements that transport liquids plug up. The compartment is the least common denominator of the tree. All the types of cells found in the woody stem of a tree will be found in each compartment When microorgani sms invade tree stems through wounds, they do so in succession s. Bacteria, nondecay fungi , and decay fungi are often intimately associated in this invasion process. When microorganisms invade, they first su rmount the chemical protec· tive barriers set up by the tree and then move into the tree from compartment to compartment The weakest walls of a compartment are the tops and bottoms, and the inner walls. The side wa lls are fairly strong. When all these walls fa ll to the invading microorganisms, there is another wall that begins to form. The wall formed by the cambium after wounding is the barrier zone. This wall confines the in · vasion to the wood present at the time of wounding. The new "trees" or rings that continue to form are then protected from invasion unless new wound s are inflicted. When new wounds are inflicted at later times, multiple columns of defect develop. An understa nding of CODIT will help to clarify many misconceptions about decay.

Decay is a natural process. The breakdown of dead organic matter is essential for new life.

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Fungi are the major group of microorganisms that decay wood. In many cases fung i accomp lish this on ly in association with other organisms, especially bacteria.

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Wood -inhabiting microorganisms enter trees through wounds. Wounds start the processes that can lead to decay. And decay is a major cause of damage to trees.

Decay

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1,p.,.ci,jU()US hardwoods and ti nJoical trees

Small animals

Insects

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Fire

Large anima ls

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But, before explaining how • start the decay process, necessary to understand a tree is constructed. A highly compartmented p.laij1!i~ " -' ·