Wood and Forest

by William Noyes

VEGETABLE ENEMIES.

Under this head may be classed, in addition to fungi, a number of unrelated plants, including such as: moosewood and dogwood, Fig. 80, which crowd out young trees; vines, like bitter-sweet, which wind about trees and often choke them by pressure, cutting thru the bark and cambium; saprophytes, which smother the foliage of trees, of which Spanish moss, Fig. 47, [p. 201], is an example; and finally such parasites as the mistletoes, which weaken and deform the trees.

Fig. 80. A "Forest Weed," Flowering Dogwood. North Carolina. U.S. Forest Service.

The most important of the vegetable enemies of trees are fungi. It should be remembered, however, that, without the decay produced by them, the fallen trees would soon cover the ground, and prevent any new growth, thus destroying the natural forest.

Every tree, as has been noted ([p. 17]), is composed of two parts, one part, including leaves, young branches, roots and sap-wood, living, and the other part, namely, the heart-wood, practically dead.

Fungi that attack the live parts of a tree are called parasites, while those that live on dead trunks and branches are designated as saprophytes. The line, however, between these two classes of fungi is not well defined, since some parasites live on both living and dead wood. The parasites are of first importance, for, since they kill many trees, they control to a large extent the supply of living timber.

Nearly all parasitic fungi have two portions, an external fruiting portion which bears the spores—which correspond to the seeds of flowering plants—and an internal portion consisting of a tangle of threads or filaments, which ramify the tissues of the tree and whose function is to absorb nutriment for the fungus. Fungi are classified botanically according to the spore-bearing bodies, their form, color, etc.

The parasitic fungi which are especially destructive to wood are those that have naked spores growing on exposed fruiting surfaces (the Hymenomycetes). In toadstools (the agarics) these exposed surfaces are thin, flat plates called gills. In the polypores, which include the shelf fungi, the spore surfaces are tubes whose openings constitute the pores. In the dry-rot, or tear fungus (Merulius lacrymans), the spore surfaces are shallow cavities.

Some varieties, called true parasites, develop in uninjured trees, while others, called wound parasites, can penetrate the tissues of trees, only where a cut or injury makes a suitable lodgment for the spores. Some fungi attack only a single species of trees, others whole genera; some attack only conifers, others deciduous trees, while a few attack trees of nearly all kinds alike.

Fungal spores when brought in contact with a wound on a tree or other suitable place, and provided with suitable conditions of growth, germinate, penetrate the tissues and grow very rapidly. These spores send out long threads or filaments which run thru the cells lengthwise and also pierce them in all directions, soon forming a network in the wood called the mycelium.

Rotting, in a large number of cases, is due to the ravages of fungi. This sometimes shows in the color, as the "red rot" of pine or the "bluing" of ash. Sometimes as in "pecky" or "peggy" cypress, the decayed tracts are tubular. More commonly the decayed parts are of irregular shape.

The decay of wood is due to the ravages of low forms of plant life, both bacteria and fungi.

A few of the more destructive forms may be noted.

Trametes pini (Brot.) Fr. Foremost among the timber destroying fungi is the large brown "punk" or "conch" found in its typical development on the long-leaf and short-leaf pines, Pinus palustris and Pinus echinata, Fig. 81. The fruiting bodies form large masses which grow out from a knot, oftentimes as large as a child's head. They are cinnamon brown on the lower surface, and much fissured and broken, on the black charcoal-like upper surface. This fungus probably causes four-fifths of the destruction brought about by the timber destroying fungi. It occurs on most of the conifers in the United States which have any value as lumber trees, and brings about a characteristic white spotting of the wood, Fig. 82, which varies with the kind of tree attacked. (Von Schrenk, Agric. Yr. Bk., 1900, p. 206.)

Fig. 81. A "Conch," the fruiting body of Trametes pini, on Sugar Pine. [Agric. Year Book, 1900, Pl. XXII, Fig. 2.]

Fig. 82. Effect of Fungus. (Trametes pini.) U. S. Dept. Agric.

Fig. 83. "Shelf" Fungus on Pine. a. Sound wood; b. Resinous "light" wood; c. Partly decayed wood or punk; d. Layer of living spore tubes; e. Old filled-up spore tubes; f. Fluted upper surface of the fruiting body of the fungus, which gets its food thru a great number of fine threads (the mycelium), its vegetative tissue penetrating the wood and causing its decay. [After Hartig.

Of the shelf fungi, which project like brackets from the stems of trees, and have their pores on their under surfaces, one of the commonest in many localities is the yellow cheese-like Polyporus sulphureus, Fig. 83. This is found on oak, poplar, willow, larch, and other standing timber.

Its spawnlike threads spread from any exposed portion of cambium into the pith-rays and between the annual rings, forming thick layers of yellowish-white felt, and penetrating the vessels of the wood, which thereupon becomes a deep brown color and decays.

Of the umbrella-shaped gill-bearing fungi, a yellow toadstool, called the honey mushroom (Agaricus melleus), is a good example, Fig. 84.

Fig. 84. Honey Mushroom. Agaricus melleus. 1. Cluster of small sporophores. 2. Larger sporophore with root-like organ of attachment. Forestry Bulletin 22. Plate XII, Figs. 1 and 2.

This fungus, of common occurrence in the United States as well as in Europe, is exceedingly destructive to coniferous trees, the white pine in particular suffering greatly from its attacks. It also fastens upon various deciduous species as a parasite, attacking living trees of all ages, but living as well upon dead roots and stumps and on wood that has been cut and worked up, occurring frequently on bridges, railroad ties, and the like, and causing prompt decay wherever it has effected an entrance. The most conspicuous part of the fungus is found frequently in the summer and fall on the diseased parts of the tree or timber infested by it. It is one of the common toadstools, this particular species being recognized by its yellowish color, gills extending downward upon the stem, which is encircled a little lower down by a ring, and by its habit of growing in tufts or little clumps of several or many individuals together. It is also particularly distinguished by the formation of slender, dark-colored strings, consisting of compact mycelium, from which the fruiting parts just described arise. These hard root-like strings (called rhizomorphs) extend along just beneath the surface of the ground, often a distance of several feet, and penetrate the roots of sound trees. By carefully removing the bark from a root thus invaded the fungus is seen in the form of a dense, nearly white, mass of mycelium, which, as the parts around decay, gradually produces again the rhizomorphs already described. These rhizomorphs are a characteristic part of the fungus. Occurring both in the decayed wood from which they spread to the adjacent parts, and extending in the soil from root to root, they constitute a most effective agency in the extension of the disease. * * *

External symptoms, to be observed especially in young specimens recently attacked, consist in a change of the leaves to a pale sickly color and often the production of short stunted shoots. A still more marked symptom is the formation of great quantities of resin, which flow downward thru the injured parts and out into the ground. (Forestry Bulletin No. 22, p. 51.)

Of the irregular shaped fungi, one of the most destructive is a true parasite, i.e., one that finds lodgment without help, called Polyporus annosus and also Trametes radiciperda, Fig. 85. It is peculiar in developing its fructifications on the exterior of roots, beneath the soil. Its pores appear on the upper side of the fructifications. It attacks only conifers.

Its spores, which can be readily conveyed in the fur of mice or other burrowing animals, germinate in the moisture around the roots: the fine threads of "spawn" penetrate the cortex, and spread thru and destroy the cambium, extending in thin, flat, fan-like, white, silky bands, and, here and there, bursting thru the cortex in white, oval cushions, on which the subterranean fructifications are produced. Each of these is a yellowish-white, felt-like mass, with its outer surface covered with crowded minute tubes or "pores" in which the spores are produced. The wood attacked by this fungus first becomes rosy or purple, then turns yellowish, and then exhibits minute black dots, which surround themselves with extending soft white patches. (Boulger, p. 73.)

Fig. 85. 1. Stump of Norway Spruce, with a sporophore of polyporus annosus several years old; the inner portions of the stump wholly decayed.

2. Roots of a diseased spruce tree, with numerous small sporophores of polyporus annosus attached. Forestry Bulletin 22, Plate XIII, Figs. 1 and 2.

Of the fungi which attack converted timber, the most important is "dry rot" or "tear fungus" (Merulius lachrymans), Fig. 86. It flourishes on damp wood in still air, especially around stables and ill ventilated cellars. It gets its name lachrymans (weeping) from its habit of dripping moisture.

The fungus destroys the substance of the timber, lessening its weight and causing it to warp and crack; until at length it crumbles up when dry into a fine brown powder, or, readily absorbing any moisture in its neighborhood, becomes a soft, cheese-like mass. * * * Imperfectly seasoned timber is most susceptible to dry rot: the fungus can be spread either by its spawn or by spores, and these latter can be carried even by the clothes or saws of workmen, and are, of course, only too likely to reach sound wood if diseased timber is left about near it; but on the other hand dry timber kept dry is proof against dry rot, and exposure to really dry air is fatal to the fungus. (Boulger, p. 75.)

Fig. 86. Portion of the mycelium of dry rot or tear fungus, Merulius lachrymans. This cakelike mass spreads over the surface of the timber. In a moist environment pellucid drops or "tears" distil from its lower surface: Hence its name. [Ward: Timber; Fig. 21.]

About all that can be done to protect the forest against fungi is to keep it clean, that is, to clear out fallen timber and slash, and in some cases to dig trenches around affected trees to prevent spreading or to cut them out and destroy them. Such methods have heretofore been too expensive to employ in any ordinary American forest, but the time is at hand when such action will prove profitable in many localities.

For the preservation of cut timber from decay, several methods are used. Fungi need heat, air, moisture and food. If any one of these is lacking the fungus cannot grow. Air and heat are hard to exclude from wood, but moisture and food can be kept from fungi. The removal of moisture is called seasoning, and the poisoning of the food of fungi is a process of impregnating wood with certain chemicals. Both these processes are described in Handwork in Wood, Chapter III.