The Major Reason Why Wood-inhabiting Microorganisms Survive is that They Become Established in Succession.
THE TREE DECAY PROCESSES START WITH A WOUND-a break in the protective bark that exposes the xylem. New space and nutrients become immediately available to a wide variety of organisms-bacteria, nondecay fungi, decay-causing fungi, algae, mosses, lichens, insects, slugs, spiders, and small animals. The competition is intense. Many organisms compete, but as time passes, fewer and fewer are successful. Environmental factors-rain, ice, snow, wind, heat, cold-affect their survival. And, while the wound surface battle rages, those living wood cells that are behind the wound are REACTING to the injury and infection. The normal physiological processes give way to new protective processes. Shifts in metabolism occur. Materials that are poisonous to some organisms are formed in the tree cells. In a sense, the tree begins to form a protective chemical shield around and immediately behind the wound. (fig. 11)
As time passes, fewer species of organisms survive on the wound surface. The concentration of any one group of organisms on the wound surface may fluctuate greatly if there are temperature extremes in the seasons. But now most of the action is inside the tree. A look into the tree after a year shows that a few microorganisms surmounted the chemical barriers formed by the tree. The microorganisms either used the protective materials in the barrier as nutrients or altered these materials in such a way that they were no longer toxic. The protective materials are mostly phenolic compounds in angiosperms and terpenes in gymnosperms. Oxidation and polymerization of these materials take place after wounding. Usually, but definitely not always, the microorganisms that are the first to infect are bacteria and nondecay fungi. In some cases, decay-causing fungi are first. The microorganisms that are the first to infect are called PIONEERS. Which microorganisms become the pioneers is affected gready by many factors-time of year of wounding; type, position, and severity of wound. The pioneers in turn affect greatly the species of microorganisms that follow in the succession. And, the species that follow will affect greatly the rate and type of wood alteration. Successions are orderly, but complex. (fig. 12)
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