Part III

21.--ImiJtrlcct imtuful i branch, where it is inserted in the tree, makes a little hole in the first coat of living tissue formed o'er the live wood after its death. The 31 edg'ct* of tliis hole make a soi"t of ctjllar about the base of the dead branch, and as a new layer is added eaeh year they press it more and more tif^htly. So strong does this compression of the living wood become that at last what remains of the dead tissue has so little sti'ength that the branch is broken ofl' by a storm or even "falls of its own weight. Then in a short time, if all goes well, the hole closes, and after a while little or no exterior trace of it I'eniains. Knots, such as those which are found in boards, are the marks left in the trunk by l)ranchc.s which have disappeared. THE CULMINATION OF GBOWTH. While the young trees are making clean trunks bo rapidly during the period of greatest yearh* height growth they are also making their greatest annual gains in diameter, for these two forms of growth gen- A erally culminate about the same time. little later, if there is an' difference, the young forest's highest yearly rate of growth in volume is also reached. For a time these three kinds of growth keep on at the same rate as in the past, but afterwards all three begin to decrease. Growth in diameter, and in volume also, if the trees are sound, goes on until extreme old age, but height growth sinks very low while the two others are still strong. For many years before this happens the struggle between the trees has not been so deadly, because they have been almost without the means of overtopping one another. When the end of the period of principal height growth is reached the trees are interfering with each other very little, and the struggle for life begins again in a different way. As the principal height growth ceases, and the tops no longer shoot up rapidly above the side branches, the crowns lose their pointed shape and become compara- tively flat. The chief reason why trees stop growing in height is that they are not able to keep the upper parts of their crowns properly supplied with water above a certain distance from the ground. This distance varies in different kinds of trees, and with the health and vigor of the tree in each species, but there is a limit in every case above which the water does not reach. The power of the pumping machinery, more than any other quality, determines the height of the tree. THE END OF THE STRUGGLE. Now that the tree can no longer expand at the top, it must either suffer a great loss in the number of its leaves or be able to spread at the sides: for it is clear that not nearly so many leaves can be exposed to the light in the flattened crown as in the pointed one. just as a pointed roof has more surface than a flat one (fig. 22). It is just at this time, too, that the trees begin to bear .seed most abundantly, and it is of the greatest importance to each tree that its digestive appa- 32 ratus in the leaves should bo able to furnish a large supply of digested food. Consequeiitlj tlie struggle for space is fiercely renewed, only now the trees no longer attempt to overtop one another, having lost the power, but to crowd one another awaj' at the sides. The whole forest might sufler severely at this point from a deadlock such as sometimes happens in early youth were it not for the fact that the trees, as they grow older, become more and more sensitive to any shade. Many species which stand crowding fairly well in 3'outh can not thrive in age unless their crowns are completely free on every side. Each of the victors in this last phase of the struggle is the sur- vivor of hundreds (or sometimes even of thousands) of seedlings. Among verj' numerous competitors they have shown themselves to be the best adapted to their surroundings. Natural selection has niade it clear that these are the best trees for the place. These are also the trees which bear the seed whence the younger generations spring. Their offspring will inherit their fitness to a greater or less degree, and iti their turn will be subjected to the .same rig(M-ous test, by which only the best are allowed to roach matui'it}'. Under this sifting out of the weak and the unfit, our native trees have been prejiarod through thousands of generations to moot the conditions under which they must live. This is why they are so much more apt to succeed than species from abroad, which have not been Fig. 22.-- DiuKiiuu to show win- a stmrply coiiioal crown receives more light than a flat one. fitted for our climate and soil by natural selection. The forest which we .saw first in the .seed has now pa.ssed through all the more vigorous and active stages of its life. The trees have become standards and veterans, and large enough to 1)0 valuable for lumber. Kaj)id growth in height has long been at an end, diameter growth is slow, and the forest as a whoh; js increasing very little in volume as time goes on. The trees are I'ijic fni- tiie harvest. Out of the many things wliic li MiJLiht happen to our malure forest, wo will onlv consider three. DEATH FROM WEAKNESS AND DECAY. In the first place, we will suj)])ose that itstands untouciieil until, like the trees of the virgin forest, it meets its death from weakness and decay. The trees of the mature primeval forest live on, if no accidents intervene, almost at peace among themselves. At length all conflict between them ends. The whole power of each tree is strained in a new struggle against death, until at last it fails. One by one the old trees disappear. But long before they go the fQi'erunners of a new 33 genpration have sprung up wherevei* light camo in between their isolated crowns. As the old trees fall, with intei'vals often of inan}^ years between their deaths, young growth of various ages rises to take their place (fig. 2?)), and when the last of th(>. old forest crop has vanished there may be differences of a hundi-ed }-(>ars among the young trees which succeed it. An even-aged crop of considerable extent, such as wc have been consideinng, is not usual in the virgin forest, where trees of \ery different ages grow side bj' side, and when it does occur the next generation is far less uniform. The forest whose history has just been sketched was chosen, not because it represents the most common type of natural forest, but because it ilkistrates better than any other the progress of forest growth. The wood of a tree which dies in the forest is almost wholly wasted. For a tmie the rotting ti-unk may serve to retain moisture, but there is little use for the carbon, oxygen, and hydrogen which make up its greater part. The mineral constituents alone form a useful fertilizer, but most often there is already an abundance of similar material in the soil. Not only is the old tree lost, but evei- since its maturity it has done little more than intercept, to no good purpose, the light which would otherwise have given vitality to a valuable crop of younger trees. It is only when the ripe wood is harvested properly and in time that the forest attains its highest usefulness. 2G900--No. 173--03 3 173 31 DESTRUCTIVE LUMBERING. A ficcond thing wliich may happen to a forest is to be cut down without care for the future (iig'. 2J:). The yield of a forest lumbered in the usual way is more or less thoroughly harvested, it is true, ))ut at an enormous cost to the forest. Ordinary lumbering injures or destroys the 3'oung growth. ))oth in the ]irpsent and for the future, provokes and feeds fires, and does harm of many other kinds. In many cases i-i(j. .1.-- lK->lniLlnL' llDlll -t I,m1u,,,,,1 Ijrlt, Uumbol(it Count;, LaL its result is to aniiiiiilatc the productive capacity of forest land for tens or scores of years to couk*. CONSERVATIVE LUMBERING. Correct methods of forestry', on the other hand, maintain and increase l)otIi the productiveness and the capital value of forest land; harvest the yield far more comj^letely than ordinary lumbering, although less rapidly; prepare for, encourage, and preserve the young growth; tend to keep out fires; and in general draw from the forest, while protecting it, the best return which it is capalile of giving. The application of such methods is the third possibility for the crop just described, and in their application is to be found the wisest, safest, and most satisfactory way of dealing with the forest. Then- iiiT still iiiiiny ))liiccs in tlic I'nitprl States, however, where transportiitioii is so costl}- that, as yet, forestry NA'ill not pay from a business point of view . ENEMIES OF THE FOREST. The fofesi is threatened by iii;my ciiciiiics, ol' wiiich Hiv and reckli'ss lumbering are th(>- worst. Tn the United States sheep grazing and w ind eom(> next, (battle and horses do much less damage than sheep, and snow break is less costly than windfall. 1 landslides, floods, insects, and fungi are sometimes very harmful. 1 ii certain situations numbers of trees are killed by lightning, which has also been known to set the woods on fire, and the forest is attacked in man}' other waj's. For example. l)irds and s(|uirrels often prevent young growth by devouring great ([uantities of nuts and other seeds, while porcupines and mice fr(M|U('ntly kill young trees by gnawing away thcii' bark. MAN AND NATURE IN THE FOREST. Most of thes(> I'oes may be called natural enemie>, for they would injure the forest tc,) a greater i>i' less (>xtent if the action of man were altogether removed. Wild animals would take the place of domestic sheep and cattle to some degree, and fire, wind, and insects would still attack the forest. But many of the most serious dangers to the forest are of human origin. Such are destructive lumbering (tig. 2-4) and excessive taxation on forest lands, to which nuich bad lumbering is directly due. So high are these taxes, for in many cases they amount to 5 or even <i per cent yearly on the market valuta of the forests, that the owners can not afl'ord to pay them and hold their lands. Consequently they are forced to cut or sidl their timl)ei- in haste and without regard to the future, ^^'h(n tlie timber is gone the owners refuse to pay taxes an- longer, and tlie devastated lands revert to the State. Man^ thousand square miles of forest have been ruined by reckless lumbering, l)ecause heavy taxes forced the ownei's to realize quickly and once for all upon their foi'est land, instead of cutting it in a way to insure valuable future crops. For the same reason many counties ai'e now poor that might, with i'(>asonal)le taxation of timber land, have been flourishing and rich. GRAZING IN THE FOREST. Whether o-razing animals are comparatively' harmless to the forest or among its most dangerous enemies depends on the age and character of the woods as well as upon the kind of animals that graze. A voung forest is always more exposed lo such injury than an old one, and steep slopes are more subject to damage than more level o-round. Whether the young trees are conifers, and so more likely 36 to suffer fi'oni tranipling- than from being eaten, or broadleaf trees, and so n>ore likely to be devoured, they should be jjrotected from pasturing animals until they arc large enough to be out of danger. GRAZING AND FIBE. Grazing in the forest does harm in three ways. First, it is a fertile cause of forest fires. Burning the soil cover of grass and othci' plants improves the grazing, either permanently, by destroying the forest and so extending the area of pasturage, or temporarily, })y -- Fig. 25. Baud of sheep in a forest reserve. Cascade Mountains, Wa 5,�00 feet. County, Greg. Altitude, improving the quality of the feed. For one or the other of these objects, but chiefl}^ for the latter, vast areas are annually burned over in nearly every part of the United States where trees grow. The great majority of these fires do not kill the old trees, but the harm they do the forest and, eventually, the forage plants themselves, is very serious indeed. The sheepmen of the West are commonly accused of setting many forest fires to improve thi> grazing, and they are also vigorously defended from this charge. Rut the fact remains that large areas where sheep now graze would be covered with forests except for the action of more or less I'ccent fires. 37 TRAMPLrHG. Trampling is the second way in which grazing animals injure the forest. Cattle and' horses do comparatively little harm, although their hoofs compact the soil and often tear loose the slender rootlets of small trees. Sheep, on the contrary, are exceedingly harmful dig. 25), especiall}' on steep slopes and where the soil is loose. In such places their small, sharp hoofs cut and powder the soil, break and overthrow the young trees, and often destroy promising young foi'ests altogether. In many places the effect of the trampling is to destroy the forest floor and to interfere very seriously with the flow of streams. In the Alps of southern France sheep grazing led to the destruction, rirst, of the mountain forests, and then of the grass which had replaced them, and thus left the soil fully exposed to the rain. Great floods followed, beds of barren stones were spread over the fertile fields by the force of the water, and many rich valleys were almost or altogether depopulated. Besides the loss occasioned in this way, it has cost the French people tens of millions of dollars to repair the damage begun by the sheep, and the task is not yet finished. The loss to the nation is enormously greater than any gain from the mountain pastures could have been, and even the sheep owners themselves, for whose profit the damage was done, were losers in the end, for their industry in that region was utterly destroyed. BROWSING. Th(> third way in wliicli grazing animals injure the forest is by feeding on the young trees. In the western part of the ITnited States, where most of the forests sire evergreen, this is far less important than the damage from either tire or trampling, for sheep and other animals seldom eat young conifers if they can get other food. Even where broadleaf trees prevail browsing rarely leads to the destruction of any forest, although it commonl}- results in scanty young growth, often maimed and luisound as well. Goats are especially harmful, and where tlicy abound the healthy reproduction of broadleaf trees is practically impossible. In the United States they are fortunately not common. Cattle devour tender young shoots and branches in vast quantities, often living for months on little else, and sheep are destructive in the same wa}'. Hogs also find a living in the forest, but they are less harmful, because a large part of their food consists of seeds and nuts. East of the Great Plains very large numbers of cattle and hogs are turned into the woods, but sheep grazing in the forest is most widel^v developed in the West, and especially iu California, where it should be prevented altogether, in Oregon and Washington, where it should be regulated and restricted, and in some interior regions, like Wyoming and Mew Mexico, when; it 88 should be rigidly' excluded from all sleep inountnin reo-ions, and eareI'ulh^ regulated on niui'e level ground. FOREST INSECTS. Insects are constantly injuring the forest, just as year by year they bring loss to the farm. Occasionally their ravages attain enormous proportions. Thus a worm, which afterwai'ds develops into a sawflv, has since 18S3 killed nearly every full-grown larcli in the Adirondacks l)V eating away the leaves. Even the small and vigorous larches do not escape altogether from these attat'ks. Conifers, such as the larch and spruce, are much more likeh' to sutler from the attacks of insects than broadleaf trees. About the year 187t) small bark beetles began to kill the mature spruce trees in the Adirondacks, and ten years later, when the worst of the attack was past, the forest had been practically deprived of all its largest spruces. This pest is still at work in northern New Hampshire and in iSIaine. FOREST FUNGI. Fungi attack the forest in many ways. Some kill the roots of trees, some grow upward from the ground into the trees and change the sound wood of the trunks to a useless rotten ma.ss, and the minute spores (or seeds) of others float through the air and come in contact with every external part of the tree above ground. Wherever the wood is expo.sed there is danger that spores will find lodgment and breed disea.se. This is a .strong reason why all wounds, such as those made in pruning, should be covei-ed with some substance like j)aint or tar to exidude the air and the sj)oi-es it carries. WIND IN THE FOREST. The effect of wind in the virgin forest is not wholly injurious. Although in many regions it overthrows great