Part II

in one place and live with many others elsewhere. The Western Yellow Pine, which forms, on the plateau of central Arizona, perhaps the largest pure pine forest of the earth, is frequently found growing with othei' species in the mountains, especially in the Sierra Nevada of central California. 22 Trees which occupy the yrouiid to the exclusion of all others do so l>ecaus(> th(M- succeed hcttcr. under the con<litious, than tlieir comiieti- Fi'i. ]7.--Clicstiiut sprouts from the stump. tors. It may he that they are al)le to get on with le.ss water, or to grow on poorer soil, their rate of growth or power of repi-oduction 23 may he gi'eatei-, or there may l>e some other reason why they are better titted for theii' surroundings. But the gregarious trees are not all alike in their ability to sustain themselves in different situations, while the differences between some of the mixed-forest species are very marked indeed. Thus, Black Walnut, as a rule, grows only in rich, moist soil and Beech only in damp situations. Fire Cherry, on the other hand, is most common on lands which have been devastated l\y tire, and the Rock Oak is most often found on dry, barren ridges. The Tupelo or Black Gum and the Red ^Nlaple both grow best in swamps, })ut it is a conmion thing to find them also on dry, stony soils at a distance from water. The knowledge of such ([ualities as these is of great importance in the management of forest lands. REPRODUCTION BY SPROUTS. Besides reproduction from seed, which plays so large a part in the struggle for the ground, reproduction })y sprouts from old roots or stumps (tig. 17) is of great importance in forestry. Trees differ very much in their power of sprouting. In nearh' all conifers except the California coast Redwood, which has this ability beyond almost ever}' other tree, "it is lacking altogether. The Pitch or Jack Pine of the Eastern United States has it also to some extent, but in most places the sprouts usually die in early youth and seldom make mer- chantable ti'ees. In the broadleaf kinds, on the other hand, it is a general and very valuable quality. Young stumps, as a rule, are much more productive than old ones, although some prolific species, like the Chestnut, sprout plentifully in old age. Other species, like the Beech, furnish numerous sprouts from young stumps and very few or none at all from old ones, and still others never sprout freely even in early youth. THE LIFE OF A FOREST. The history of the life of a forest is a story of the help and harm which the trees receive from one another. On one side every tree is engaged in a relentless struggle against its neighbors for light, water, and food, the three things trees need most. On the other side, each tree is constantly working with all its neighbors, even those which stand at some distance, to bring about the best condition of the soil and air for the growtli and fighting power of every other tree. A COMMUNITY OF TREES. The life of a community of trees is an exceedingly interesting one. A forest tree is in manj' ways as nuich dependent upon its neighbors for .safety and food as are the inhabitants of a town upon one another. The difference is that in a town each citizen has a special calling or occupation in which he works for the service of the commonwealth, while in tiie forest everv tree contriliutes to the general welfare in 24 nearh' all the ways in which it is benefited by the conimunit}-. A for- est tree helps to protect its neighlioi-s against the wind, which might overthi'Gw them, and the sun, which is ready to dry up the soil about their roots or to make sun cracks in their bark by shining too hotly upon it (tig. 18). It enriches the earth in which they stand b^- the fall of its leaves and twigs, and aids in keeping the air about their crowns, and the soil about~their roots, cooler in summer and warmer in winter than it would he if each tree stood alone. With the others it forms a Fig. is.--Forest trees stanrtiHK h common canopy under which the seedlings of al! the members of this protective union are sheltered in early j'outh, and through which the beneficent influence of the forest is pi-eservedand extended far beyond the spread of the trees themselves. But while this fruitful cooperation exists, there is also present, just as in a village or a city , a vigorous strife for the good things of life. For a tree the l)est of these, and often the hardest to get. are water for the roots and space and light for the crown. In all l)uf very di-y places there is water enough for 25 all the trees, and often more than enough, as for example in the Adirondack forest. The struggle for space and light is thus more important than the struggle for water, and as it takes place above ground it is also much more easily observed and studied. Light and space are of such impoi'tance because, as we have seen, the leaves can not assimilate or digest food except in the presence of light and air. The rate at which a tree can grow and make new wood is decided chiefly by its ability to assimilate and digest plant food. This power depends upon the number, size, and health of the leaves, and these in turn u]ion th(> amount of space and light which the tree can secui'e. THE LIFE OF A FOREST CROP. The story of the life of a roicst croi) thi'ii l:irg('ly an account of the competition of the trees for liglit an �ini. Mini. altlioiii'-li the "erv strength which enables them to carry on the fight is a result of their association, still the deadly struggle, . in which the victims arc many times more in number than those which survive, is apt alone to absorb the at- tention. Yetthe mutual help of the trees to each other is always going quieth'on. Every tree continually comforts and assists the other trees, which are its friendly enemies. The purpose here is to follow the progress of a forest crop of uni- form age from the seed through all the succes- sive phases of its life until it reaches matu- rity, bears seed in its turn, and finallv de- m ,. . cbnes . ,.,.." tertility and, A Fl... I'J.-- Wllilu Pillr sc.-.llilii;, sllmvi].!,Mll..ykIl.Urr.l()t^. strength until at last it passes away and its place is tilled by a new generation. The life history which we ai-e about to follow , as it unfolds itself through the course of several hundred yeai's, is full of struggle 26 and danger in youth, restful and dig-nitied in age. The changes which pass over it are vast and full of the deepest interest, hut they are very gradual. From beginning to end one stage melts insensibly into the next. Still, in order to study and describe them (H)nveniently, each stage must have limits and a name. THE SEVEN AGES OF A TREE. Avery practical way of classifying trees according to size is the following: Young trees which have not yet reached a height of 3 feet are sesdlliK/x (tig. 19). They are called .seedlings in spite of the fact that any tree, of whatever age, if it grew from a seed, is properly called a .seedling tree. Trees from 3 to 10 feet in height are huuiU fniplinyx, and from 10 feet in height until they reach a diameter of i inches they are hiiyi' saplings. Small p<ilex are from 4- to 8 inches in diameter, and Imyt^ j>olfS from Sto 12 inches in diameter. Trees from 1 to 2 feet through are standards, and, hnally, all trees over 2 feet in diameter are veterans. It is very important to remember that all these diameters are measured at the height of a man's chest, about 4 feet 6 inches from the ground. In forestry this is, roughly speaking, the general custom. HOW THE CROP BEGINS. Let us imagine an abundant crop of tree seeds lying on the ground How in the forest. they came there does not intere.st us at present; we do not care to know whether they were carried by the wind, as often happens with the winged seeds of manj' trees, such as pines and maples, whether the squirrels and birds dropped and planted some of them, as they frequently do acorns and chestnuts, or whether the We old trees stood closely about and sowed the .seeds themselves. will suppose them to be all of one kind, and to be scattered in a place where the soil, the moisture, and the light are all just as thcT should 1)6 for their successful germination, and afterwards for the later stages of their lives. Even under the best conditions a con.siderable part of the fallen .seed may never germinate, but in this case we will assume that half of it succeeds. As each seed of our forest germinates and pushes its tirst slendei- rootlet downward into the earth, it has a very uncertain hold on lite. Even for some time afterwards the danger from frost, drynes.s, and excessive moisture is very serious indeed, and there are many other foes by which the young .seedlings may be overcome. It sometimes happens that great numbers of them peri.sh in their earliest youth becau.se their roots can not reach the soil through the thick, dry coating of dead leaves which covers it. But our young trees pass through the beginning of these dangers with comparatively little loss, and a plentiful crop of seedlings occupies the ground. As yet, however, each little treo stands free from those about it. As j'et, too, the life of the ()iiny foivst iiuiy he threatened or i'\eii destroyed by any one of the enemies already mentioned, or it may suffer just as severely if the cover of the older trees above it is too dense. In the beginning of their lives seedlings often i-equire to ])e protected In' the shade of their elders, but if this protection is too long continued they sutler for want of liglit, and are either killed outright or live only to drag on stunted and unliealthy lives. THE FOREST COVER ESTABLISHED. The (Top which we are following has had a suitable proportion of shad(( and light during its earliest years, and the seedlings have spread until their crowns begin to meet. Hitherto each little tree has had all the space in the ail' and soil that it need(>d for the expansion of its top Fk:. 20.--Youug White Pine seedlings whu�e li>wer braiiehes have just begun to iuterfere. and roots. This would have been entirely good, except that meanwhile the soil about the trees has been more or less exposed to the sun and wind, and so has become dryer and less fertile than if it had been under cover, and consequently the growth has been slow. Hut now that the crowns are meeting, the situation becomes wonderfully changed. The soil ])egins to improve rapidly, because it is ])rotected by the cover of the meeting crowns (tig. 2(�) and enriched by tlie leaves and twigs which fall from them. THE BEGINNING OF THE STRUGGLE. In .so far the conditions of life are better, and in consec{uence the growth, and more especially the height growth, begins to show a marked increase. On the other hantl, till the new strength is in 28 immediate demand. With the added vigor which the trees are now helping eacli other to attain, comes the most urgent need for rapid development for the decisive struggle at hand. The roots of the j^oung trees contend with each other in the .soil for moi.sture and the plant food which it contains, while in the air the crowns struggle for space and light. The latter is by far the more important battle. The victors in it overcome by greater rapidity of growth at the ends of the branches, for it is by growth there, and there only, that trees increase in height and spread of crown. Growth in this way was going on unchecked among the young trees before the crowns met, but now onlj^ the upward-growing branches can develop freely. The leaves at the ends of the side branches have now less room and, a))ove all, less light, for they are crowded and thrust aside by those of the other trees. Very often they ai'e l)ruised l)y thrashing against their neigh))ors when the wind blows, or even broken ofl' while still in the bud. Leaves exposed to such dangers are unhealthy. They transpire less than the healthy un(listui-l)ed leaves of the upper part of the crown, and more and more of the undigested food from the roots goes to the stronger leaves at the top as the assimilating power of the side leaves dwindles with the loss of light. The young branches share the fortunes of their leaves and are vigorous or sickly according to the condition of the latter. For this reason the growth of the tops increases, while that of tiie lower lateral branches, as the tops cover them with a deeper and deeper shade, becomes less and less, (iradtially it cea.ses altogether, and the branches perisli. This jirocess is called natural pruning, and from the time when it l)egiiis tlie existence of the young forest, unless it should l)e oveitakeii l>y (iic or sonic other great calainity. is practically secure. GROWTH IN HEIGHT. At this time, as we have seen, tlie crowns of all the young trees are growing faster at the tops than at the sides, for there is unlimited room a})0ve. But some are growing faster than others, (hither liecause their roots are more developed or in better soil than those of tlie trees about them, because they have been freer from the attacks of insects and other enemies, or for some similar reasons. Some trees have an inborn tendency to grow faster than others of the same species in the same surroundings, just as one .son in a familj' is often taller than the brothers with whom he was lirought up. Rapid growth in height, from whatever cause it proceeds, lirings not only additional light and air to the tree which excels in it, but also the chance to spread laterally, and so to complete the defeat of its slower rivals l>y ovei'topping liiein. 29 THE STRUGGLE CONTINUED. Those tr('(\s wliicli luivc giiiued thi.s iidviintiigc over tlieir neighl)ors are called dominant trees, while the surviving laggai'ds in the race are said to he overtopped when the}' are hopelessly l)ehind, and retarded when less badlj' beaten. Enormous numbers of seedlings and small saplings are suppressed and killed during the early youth of the forest. In the v'oung crop which we are following man}' thousands perish upon every acre. Even the dominant trees, which are temporarily free when they rise above their neighbors, speedily come into conflict with each other as they spread, and in the end the greater portion is overcome. It is a very deadly struggle, but 3'ear by 3'ear the difl'erences between the trees become less marked. Each separate individual clings to life with greater tenacity, the strife is more protracted and severe, and the number of trees which pei'ish grows liipidly smaller. But so great is the pressure when dense groups of young trees are evenly matched in size and rate of growth that it is not very unusual to tind the progress of the young forest in its early stages almost stopped and the trees uniformly sickly and undersized, on account o,f the crowding. The forest we have been following has now passed thi-ough the small-sapling stage, and is composed chiefly, but not exclusively, of large saplings. Among the overtopped and retarded trees, which often remain iu size classes which the dominant trees have long since outgrown, there are still many low saplings. Even between the dominant trees, in a healthy forest, there are alwaj'S great differences. Increase in height is now going on ra])idly among these high saplings, and either in this stage or the next a point is reached when the topmost branches make their longest yearly growth, which is one way of saying that the trees make their most rapid height growth as large saplings or smali poles. Later on, as we shall see, these upper branches lengthen much more slowly, until, in standards and veterans, the growth in height is small, and in \cry old trees finally ceases altogether. NATURAL PRUNING. While the trees ari' pushing u[) most rapidly, the side l)ranches are "most quickl}' overshaded, and the process of natural pruning goes on with the greatest vigor. Natural jiruning Is the reason why old trees in a dense forest have only a small crown high in the air, and why their tall, straight trunks are clear of branches to such a height above the ground. The trunks of trees grown in the open, where even the lower limbs have abundance of light, are branched either quite to the ground or to within a short distance of it (fig. 21). But in the forest not only are the lower side branches continually dying for want of light, but the tree rids itself of them after they are dead and so frees 30 its trunk from them entirely. When a branch dies the annual layer of new wood is no longer deposited upon it. Consequently the dead Fi�.