Introduction

SD 373 .P65 Copy 1 LlBROfJy 002 S18 I SD 373 .P65 Copy 1 COMl'XTS. The life of a tree 5 The Ilarta c )f a t ree (i The food of a tree 7 The composition of wood .S How the tree breathes t~. 8 Transpiration !) The growth of a tree 9 Tlie structure of wood 11 Atuiual rings lo Heart wood and sapwood 13 Trees in the forest 14 The various requirements of trn-s If) Re(]uirenieuts of trees for heat and moisture , IH Re(]uirements of trees for liglit 17 Tolerance and intolerance IS The rate of growth 19 The reproductive powi'r of trees 'M Pure and mixed forest -! 1 Reproduction by sprouts T.i The life of a forest '2',i A community of trees 23 The life of a forest crop '2b The seven ages of a tree 2(5 How the crop begins 2(5 The forest cover established 27 The 1 leginning of the struggle 27 (4n iwt h in height 2S The struggle continued 29 Natural pruning 29 The culmination of growth .'Jl The end of the struggle 31 Deatli fr< mi weakness and decay 32 Destructive hiiubering 34 Conservative lumbering 34 Enemies of the forest 35 Man and nature in the forest 35 Grazing in the forest 35 Grazing and tire 3t> Trampling 37 Browsing 37 Forest insects 38 Forest fungi 38 Wind in the forest 38 Snow in the forest 40 Forest fires 41 Historic forest fires 42 Means of defense 43 Surface fires 44 Ground fires 45 Back firing 46 Fire lines 47 ILLUSTRATIOXS. 1. Roots, stem, and crown of ii young 81icll)iark lli<'k(iry 2. Upturned skeleton roots of a Red Fir 3. Trunks of two Red Firs 4. Stem and crown of a Longleaf Pine 5. Cross section of wood and bark of the Western Yelli>w Pine 6. Yearly growth of a branch of Horse Chestnut 7. Perpendicular cut of wood and bark of the Western Yrll<iw riiic S. Outer surface of bark of the Western Yellow Pine 9. Wood of a spruce greatly magnified 10. Wood of Western Hemlock 1 1 Ainiual rings 1 2. A section of the common Staghorn Sumach 13. A forest of palms in .southern Florida 14. The Black Hemlock in its home 15. Young oaks starting under an old forest of pines 16. Winged seeds 17. Chestnut sprouts from the stump 18. Forest trees standing too far apart to help each other 19. A White Pine sccdiiu;.', showing the slender roots 20. Young White Pine seedlings whose lower branches have just begun to interfere 21. Imperfect natural pruning of a White Pine that stood ti>o much alone in early youth 22. I )iagram to show why a sharply conical crown receives mcire light than a flat one 23. Young growth under old trees 24. Destructive lumbering in the Coast Reflwood Belt 25. Band of sheep in a forest reserve 26. A windfall in the Olympic Forest Reserve 27. .\ young spruce loaded with snow 28. The rotting stubs of fire-killed veterans of Red Fir 29. A surface fire burning slowly against the wind 30. The effect of repeated fires 31. The result of recurring fires 32. Setting a back fire on the windward side nf a road A 33. fire line along a railroad 4 Page. 5 6 7 7 9 10 10 11 12 13 13 14 1.5 16 19 20 22 24 2.5 27 30 32 33 34 .36 39 40 41 44 45 46 46 47 A PRIMER OF FORESTRY. THE LIFE OF A TREE. The object of forestry is to discovi iiig to which forests lire hest nuitiiiued. It is distinct from arboriculture, which deals with individual trees. Forestry has to do with single trees only as they stand together on some large area whose princi})al crop is trees, and which theret'oic forms part of a forest. The forest is the most highly organized portion of the vegetable world. It takes its importance less from the individual trees whicii lielpto form it than from tile qualities which belong to it as a whole. Although it is composed of trees, the forest is far more than a collection of trees standing in on(> place. It has a population of animals and plants peculiar to itself, a soil largely of its own making, and a climate difl'erent in many ways from that of the open country. Its influence upon the streams alone makes farming possible in many regions, and everywhere it tends to prevent floods and drought. It sup- plies fuel, one of the flrst necessaries of life, and lumber, the raw material, without which cities, railroads, and all the great achievements of material progress would have been eitheilong delayed or wholly impossible. The forest is as beautiful as it is useful. The old fairy tales which spoke of it as a terrible place are wrong. No one can really know the forest without feeling the gentle influence of one of the kindliest and andap])ly the print'iples accord- -- Fi'. 1. ILodtH. stum, jiiul crown of a : Hliullbark Hickory. strongest parts of natui'e. Fi-oni (''ery point of view it is one of tlie. most helpful friends of ni;iii. Pcihaps no other natural agent has done so nuich for the human race ami has ht'cn so i-ecklessly used and so little understood. THE PARTS OF A TREE. In order rightly to understand the forest, something must first be A known about the units of which it is made up. tree, then, is a wood}- plant gi'owing up from the ground usually with a single stem (tig. 1). It consists of three parts: (1) The roots (tig. 2), which extend into the ik iK.li 1 suilln tliL In I ill r nil I \ I Mupit Pc-inuiuli \asliiiiirtci ground to a depth of y> or 4 feet, or still farther when the soil is not too hai'd and they do not find moisture enough near the surfaet^; they hold the tree in place and take up from the soil wat(n-and cei-tain mineral substances which the tree needs in its growth; (2) tlie trunk or stem (fig. 3), which supports the crown and supplies it with mineral food and water from the roots; (3) the crown itself (tig. 4), with its network of branches, buds, and leaves, in which the food taken up by the tree from the soil and air is worked over and made ready to assist in the growth of the whole plant. The crown has more to do with the life of the tree than its other parts, for the most important pi-ocesses in the r(>production of tiie tree and the digestion of its food take place in the crown. For this reason, and hecuuse we can control its shape and size more easily and directly than tliut (if th(! roots or trunk, the crown is of special interest to the M forester. 1 1 is idniost exclusively with the crowns that he has to deal in tcnilini^- a rr(i[) of trees and jii-ejiarinj^- the way for tiie sut'ceedino' 8 holds in solution. These sire the earthy constituents of the tree, which reappear in the form of ashes when any part of it is burned. The water which contains these materials goes straight from the roots to the leaves, in which a most important process in the feeding of the tree takes place. The process is the assimilation or taking up and breaking up, by the leaves, of carbonic-acid gas from the air. It goes on only in the presence of light and heat, and through the action of chlorophjdl, a substance from which the leaves and the young bark get their green color. Plants containing chlorophyll are the chief means l)y which mineral materials are changed into food, so that nearly all plant and animal life depends upon them. Plant cells which contain chlorophyll t)reak up the carbonic-acid gas with which they come in contact, retain the carbon, one of its elements, and .send back the other, oxygen, into the air. Then, .still under the influence of the sunlight, they combine the carbon with the oxygen and hydrogen of the watei' from the roots into new chemical compounds, in which nitrogen and the earth>' constituents mentioned alwve are also present; that is to sa}', the food materials which reach the tree through the roots and leaves are first digested in the leaves somewhat as food is digested in the human body, and are then sent to all living parts of the roots, stem, and crown, where thej' pass through another process of digestion, and are then either used at once in growth or stoi'ed away until the propei' moment arrives. This is the general rule, ]>ut it is believed that in some cases food taken up l)y the roots can be used without first being digested in the leaves. THE COMPOSITION OF WOOD. Wood is made up chiefly of carbon, oxygen, anil hytlrogen. ^^hen perfectly dry, about half its weight is carbon, and half oxvg<Mi and hydrogen, in almost the same proportion as in water. It contains also about 1 part in 10(1. by weight, of eai-thy constituents, and nitrogen to the same amount. When wood is buined, all these materials disappear into the air except the earthy constituents. Now, the nitrogen and water tsiken up b' the roots were originally in the air before they reached the ground. It i.s true, therefore, that when wood is burned those parts of it which came from the air go })ack into it in the form of gas, while those which came from the soil n^maiii behind in the form of ashe.s. HOW THE TREE BREATHES. Besides giving out oxygen in assimilation, trees also take in oxygen from the air through their leaves, and through the miiuite ojienings in the bark called lenticels, such as the oblong raised spots or marks 9 on the youno- l)ranches of liirch and cherry and miinv other trees. All plants, like all animals, l)i-eathe; and plants, like animals, breathe in oxyj^en and breathe out carbonic acid gas. This process of respiration or the breathini^- of the ti'ee goes on both day and night, but it is far les.s active than assimilation, which takes place only in the light. Consequently more carbonic-acid gas is taken into the ti-ee than is given out, and the surplus cai'boii remains to be used in growinsj-. TRANSPIRATION. The leaves gi'e out not only the oxygen derived from the decom- position of carbonic-acid gas taken from the air and carbonic-acid gas produced in breathing, but also great quantities of water vapor. The amount of water taken up by the roots is very much larger than is i-equired to be coml)ined witli carbon and the earthy constituents in tlie leaves. In order that fresh supplies of earthy constituents in solution may reach the leaves rap- idly the water already in them m ust be go t o u t o f t h e way . This is effected Ijy transpiration, which is the evaporation of water from all parts of the tree above ground, but principally fi-oni the leaves. Even where the bark is very thick, as on the trunks of old oaks and chestnuts, transpiration goes on through the lenticels in the Iwt- --. Cross seutioii of wood ami bark of the Western Yellow Pine, shnwinjf t\v<.> of the deep cracks in the bark, at the bottom of which lenticels an- placed. toms of the deep cracks (fig. 5). It sometimes happens, especially in spring before the leaves come out, that transpiration can not get rid of the water from the roots as fast as it rises, and that it falls in drops from tiie l)U(ls, or later on even from the leaves themselves. THE GROWTH OF A TREE. The addition of new material in the way descril)ed in the preceding pages is the foundation of growth. Except in the buds, leaves, fruit, and the twigs le.ss than a year old, this material is deposited in a thin coat over the whoie tree between the wood and the bark. The new 10 twigs grow in length by a kind of stretching, ])ut only during the tirst year. Thus it is oidv l>v means of these youngest twigs that a -- Fiu. G. Yearly ijrowlh of a brunch ui" Hur^L' (;:liL'slmit. Tin.' haml-s uf wrinkles mark the divisions between the growths of fonr snccessive years. The (iistnnce between these baitds would never have been greater thaii it was when the branch was cut. 7-- FUi. E'erpeudiciihii bark into scales by II and bark. be division ()f the tree increases in height and in spread of branches. After the tirst year their length is fixed, younger twigs stretch out from the buds. 11 and the older ones grow henceforth only in thickness (tig. 6). The fresh coat of new material mentioned above covers them year })v year. There are two layers in this coat, s<^parated hy a third one of tender forming tissues called the cambium, in which the actual making of the new substance goes on. The inner sitU' of the cambium layer forms new wood, the outer side new bark. Besides the ti'ue cambium, which forms both wood and bark, there is another cambium which makes the corky outer bark and nothing else (tigs. 7 and S). This cork cambium mu' (Micircii^ the whole tree, like tlie true caml>ium. as in the may lied Cedar, oi- it foiin little s('i);irate films i either casi' it dies from time to time and is rc-fDniu the l)ark. but in ni^arer the wood. THE STKUCTURE OF WOOD. Wood is chiefly made up of very small tul)cs or cells (tig. 9) of various kinds, which have special uses in the life of tlie tree. Some con- duct water from the roots to the crown, some store away digested food, and others merely strengthen the structure of the ^v�ood and hold it togetiier. The wood of cone-bearing or coniferous trees (like the pines and spruces) has but few kinds of cells, while that of the broadleaf trees (such as oaks and maples) is much less simple. But in each case some of the cells have thick walls and small openings, and others wide openings and very thin walls. In climates which have regularly one season of growth and one of rest, like our own, the cells of the 12 layer of new wood formed each year at the inner surface of the cam])iuni are arranged in a definite vfny. When growth ))egins in the spring, and the fresh twigs and leaves put out, there is a great demand for water in the crown to supply these moist green new parts of the tree. Water rises in most trees through the newer layers of the wood, and especiall}' through the last ring. Consequently, at first the tree makes thin-walled cells with wide openings, through which water can rise rap- idly to the ends of the branches. Later on, r r^c when the demand for water is not so great, and there is plenty of digested food to supply l)uilding material, the cells formed are narrow '^' [^V^ rC^CrV <0 '"'^' thick-walled. Thus the summer wood in each year's growth is heavier, stronger, and darker in color than the spring wood. In the wood of many broad leaf trees, such as Hr oak and chestnut, tlie spring wood is also mai'ked by a band of open tubes of larger size called ducts. In othei's, such as maple and beech, these ducts are scattered through the whole season's growth, and in all conifers, as for example the pines and cedars, they are ^r r entirely wanting. But the diti'erences in liardness and color between the growth of spring and summer are still present. It is sometimes possible to see the line which sepai'ates the growth of two seasons in the bark, as in rU the case of connnon cork, which is the outer bark of the Cork Oak, a native of southern Europe. If the trunk or branch of an oak tree is cut smoothly aci'o.ss, thin whitish lines may be seen running fi'om within outward (Hg. 10, ))lock at the right). Some of the.se lines begin in the center of the tree and others in each one of the annual rings. These are the medul- lary ra_vs, which make the silver grain in i|uartered oak and other woods. They exist Fig. 'J.-- Wuod of a si.riKi'. greatly niagniHed. -- in all kinds of trees, but in many as, for example, in the Chestnut and in most coni- -- fers they are so fine as hardly to be seen with the naked ej'e. Seasoning cracks which run across the rings of growth always follow the lines of these rays, while others most often follow along some annual ring. 13 ANNTJAL RINGS. It i.s correct to .speak of the.sc rings of gi-o\vth as '"annual rings," for as long as the tree i.s growing healthily a ring is formed each year (Kgs. 1(), 11). It i.s true that two false rings may appear in one year, hut lhe' are generally so much thinner than the rings on each side that it is not hard to detect them. Very often they do not extend entirely around the tree, as u true ring always does if the tree is sound. Whenever the growth of the tree is interrupted and begins again during the same sea.son, such a false ring is formed. This happens when the foliage is destroyed hy caterpillars and grows again in the same season, or when Fk!. 11.-- Aimuiil rings. a