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84 Chapter 8 Parasites on the Conifers The Value of Rot and Decay Indisputably beneficial fungi, as described in chapters 4 and 7, are those that unite with tree roots to form mycorrhizae. Now we come to wooddestroying fungi, those that cause wood to rot, decompose, or decay— all three words mean the same. These fungi are discussed in innumerable books devoted to tree “diseases,” describing the damage they do to timber. However, they are vitally necessary in the maintenance of living, growing forests. Without them, dead woody debris, fallen trees, logs, branches, and twigs would accumulate on the forest floor year after year without end. Just visualize it—only then can the immense importance of decomposers be appreciated. They are true recyclers (as is fire; see chapter 11). Decay Fungi The decay fungi are an entirely different set of fungus species than those forming mycorrhizae. No species is occasionally mycorrhizal and occasionally a destroyer. The fruiting body of most decay fungi is known as a conk or shelf fungus (sometimes, a bracket fungus). A conk grows on the surface of its tree host, and its hyphae grow directly into the tree’s tissues without touching the soil. Three types of conk are illustrated in figure 8.1. Their shape depends on where on a tree they grow. The majority project out like a parasites on the conifers 85 shelf from a tree’s trunk, and their hyphae grow into the trunk. Some resemble short-stemmed mushrooms and grow upright from a horizontal surface like that of a cut stump or exposed root. A few others grow as complete discs apparently on the forest floor, but their hyphae grow down into the shallow roots of the host tree. The appearance of wood decayed by these fungi depends on which of the tree’s chemical constituents the fungus consumes. The two most common constituents of wood are cellulose, forming about 50 percent of its mass, and lignin, about 30 percent. Their colors are white and rusty redbrown , respectively. Therefore, a fungus that consumes cellulose leaves leftovers of red-brown rotted wood that is mostly lignin. Conversely, if the lignin is consumed, a white rot is left. Red-brown rots are the more common kind in conifers. Most of the decay fungi are polypores (family Polyporaceae), whose spores are liberated through numerous fine pores on the lower surface of the cap or shelf. Of the fungi shown in figure 8.1, red-belted (also known as red-banded) polypore (Fomitopsis pinicola) is both common and widespread. It attacks the majority of conifers. The conk is hard, woody, and perennial, but it grows a fresh pore surface every year. The conk is either flat or hoof-shaped, and colored in concentric zones: black on the inner part and creamy white Figure 8.1. Three decay fungi on conifers. (a) Red-belted polypore. (b) Hemlock varnish conk. (c) Velvet-top fungus (or dye polypore). 86 the world of northern evergreens at the outer edge, which is smoothly rounded. The red “belt” is one of the blended zones between the color extremes. The fungus attacks dead trees, producing reddish brown, rotted wood that is divided first into neat cubes, which later crumble. This type of rot is caused by so many decay fungi, it is of little help in recognizing the fungus species that made it. A common conk in eastern forests is hemlock varnish conk (Ganoderma tsugae) (figure 8.1b). It attacks several conifers, most often eastern hemlock . When it grows as a semicircular shelf, it attaches itself to its host by a short thick stem. The conks are annual, and when fully grown in summer, they have glossy, red tops with a pale rim; they look as though they had been lacquered. Velvet-top fungus, also known as dye polypore (Polyporus schweinitzii), is another widespread and easily recognized decay fungus. Its disc is usually all brown and depressed at the center; it is covered with velvety short hairs. Sometimes it grows as a shelf near the bottom of a trunk, and sometimes (figure 8.1c) as flat discs growing up from a buried root into which its hyphae penetrate. It can spread from root to root in an infected stand. Many rot fungi attack the roots of conifers. A common one in the Pacific rain forest is laminated root rot (Phellinus weirii), found on many species, especially Douglas-fir and western redcedar. It spreads from tree to neighboring tree through root grafts, infecting...

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Additional Information

ISBN
9780801463037
Related ISBN
9780801477409
MARC Record
OCLC
966802958
Launched on MUSE
2017-01-01
Language
English
Open Access
No
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