Wood and Forest Part 37

[Ill.u.s.tration: Fig. 79. Contraction Frost Check. _U. S. Forest Service._]

VEGETABLE ENEMIES.

Under this head may be cla.s.sed, 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.

[Ill.u.s.tration: 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 cla.s.ses 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 cla.s.sified 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 const.i.tute 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 pal.u.s.tris_ and _Pinus echinata_, Fig. 81. The fruiting bodies form large ma.s.ses 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.)

[Ill.u.s.tration: Fig. 81. A "Conch," the fruiting body of _Trametes pini_, on Sugar Pine. [_Agric. Year Book, 1900_, Pl. XXII, Fig. 2.]]

[Ill.u.s.tration: Fig. 82. Effect of Fungus. (_Trametes pini._) _U. S.

Dept. Agric._]

[Ill.u.s.tration: 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 sp.a.w.nlike 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.

[Ill.u.s.tration: Fig. 84. Honey Mushroom. _Agaricus melleus._ 1. Cl.u.s.ter of small sporoph.o.r.es. 2. Larger sporoph.o.r.e 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, ma.s.s 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 const.i.tute 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 quant.i.ties 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 "sp.a.w.n" 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 ma.s.s, 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.)

[Ill.u.s.tration: Fig. 85. 1. Stump of Norway Spruce, with a sporoph.o.r.e of _polyporus annosus_ several years old; the inner portions of the stump wholly decayed.

2. Roots of a diseased spruce tree, with numerous small sporoph.o.r.es 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 ma.s.s. * * * Imperfectly seasoned timber is most susceptible to dry rot: the fungus can be spread either by its sp.a.w.n 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.)

[Ill.u.s.tration: Fig. 86. Portion of the mycelium of dry rot or tear fungus, _Merulius lachrymans_. This cakelike ma.s.s 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.

ANIMAL ENEMIES.

The larger animals working damage to our forests are chiefly rodents and grazing animals. Beavers gnaw the bark, while mice and squirrels rob the forest of seed and consequently of new trees. The acorns of white oak are particularly liable to be devoured because of their sweetness, while those of red and black oak, which afford timber of comparatively little value, are allowed to sprout, and thus come to possess the land. Hogs annually consume enormous quant.i.ties of "mast,"

_i.e._, acorns or other nuts, by pasturing in oak and other forests.

They, together with goats and sheep, Figs. 87 and 88, deer and cattle, work harm by trampling and browsing. Browsing destroys the tender shoots, especially of deciduous trees, but trampling entirely kills out the seedlings. The cutting up of the soil by the sharp cleft hoofs injures the forest floor, by pulverizing it and allowing it to be readily washed away by storms until deforestation may result, as was the case in France after the Revolution. It has cost the French people from thirty to forty million dollars to repair the damage begun by the sheep. In this country, this matter has become a very serious one on the Pacific Coast, where there are enormous flocks of sheep, and therefore the government is trying to regulate the grazing on public lands there, especially on steep slopes, where erosion takes place rapidly.[1]

[Footnote 1: The evils of grazing are increased by the fact that fires are sometimes started intentionally in order to increase the area of grazing land.]

[Ill.u.s.tration: Fig. 87. Goats Eating Foliage, New Mexico. _U.S. Forest Service._]

[Ill.u.s.tration: Fig. 88. Sheep Grazing in Forest, Idaho. _U.S. Forest Service._]

The most destructive animal enemies of the forest are the insects.

The average annual loss of trees in the United States from this cause alone has been estimated to be one hundred million dollars.

Insects have two objects in their attack on trees, one is to obtain food, as when they are in the larval stage, and the other is to provide for offspring, as do certain beetles.

The number of insect enemies of the forest is enormous. At the St.

Louis Exposition, there were on exhibit nearly three hundred such insects. These belong to some twenty orders, of which the beetles (_Coleoptera_), which have h.o.r.n.y wings and biting mouth parts, and the moths and b.u.t.terflies (_Lepidoptera_), with membraneous wings and sucking mouth parts, are the most destructive. Insects attack every part of the tree, the seed, the shoot, the flower, the root, the leaf, the bark and the wood, both standing and cut.

Of the fruit and seed pests, the most destructive are weevils, worms and gall insects.

Of the twig and shoot pests, beetles, weevils and caterpillars are the worst.

Among insects that attack roots, the periodical cicada (17 year old locust) may be noted.

The leaf pests are far more serious. They include the true and false caterpillars, moths, gall insects and plant lice.

Of the bark pests, the bark beetles are the most destructive. These are also called Engraver Beetles from the smoothly cut figures which are their burrows under the bark, Figs. 89, 90, 91.