The School Book of Forestry.
by Charles Lathrop Pack.
INTRODUCTION
Our forests, with their billions of trees, are the backbone of agriculture, the skeleton of lumbering, and the heart of industry. Even now, in spite of their depletion, they are the cream of our natural resources. They furnish wood for the nation, pasture for thousands of cattle and sheep, and water supply for countless cities and farms. They are the dominions of wild life.
Millions of birds, game animals, and fish live in the forests and the forest streams. The time is coming when our forests will be the greatest playgrounds of America. It is necessary that we preserve, protect, and expand our timberlands. By so doing we shall provide for the needs of future generations.
The forest is one of the most faithful friends of man. It provides him with materials to build homes. It furnishes fuel. It aids agriculture by preventing floods and storing the surplus rainfall in the soil for the use of farm crops. It supplies the foundation for all our railroads. It is the producer of fertile soils. It gives employment to millions of workmen. It is a resource which bountifully repays kind treatment. It is the best organized feature of the plant world. The forest is not merely a collection of different kinds of trees. It is a permanent a.s.set which will yield large returns over long periods when properly managed.
Our forest fortune has been thoughtlessly squandered by successive generations of spendthrifts. Fortunately, it is not too late to rebuild it through cooperative effort.
The work has been well begun, but it is a work of years, and it is to the youth of the country that we must look for its continuous expansion and perpetuation. A part of our effort must be directed toward familiarizing them with the needs and rewards of an intelligent forestry policy.
CHAPTER I
HOW TREES GROW AND MULTIPLY
The trees of the forest grow by forming new layers of wood directly under the bark. Trees are held upright in the soil by means of roots which reach to a depth of many feet where the soil is loose and porous. These roots are the supports of the tree.
They hold it rigidly in position. They also supply the tree with food. Through delicate hairs on the roots, they absorb soil moisture and plant food from the earth and pa.s.s them along to the tree. The body of the tree acts as a pa.s.sage way through which the food and drink are conveyed to the top or crown. The crown is the place where the food is digested and the regeneration of trees effected.
The leaves contain a material known as chlorophyll, which, in the presence of light and heat, changes mineral substances into plant food. Chlorophyll gives the leaves their green color. The cells of the plant that are rich in chlorophyll have the power to convert carbonic-acid gas into carbon and oxygen. These cells combine the carbon and the soil water into chemical mixtures which are partially digested when they reach the crown of the tree. The water, containing salts, which is gathered by the roots is brought up to the leaves. Here it combines with the carbonic-acid gas taken from the air. Under the action of chlorophyll and sunlight these substances are split up, the carbon, oxygen and hydrogen being combined into plant food. It is either used immediately or stored away for future emergency.
Trees breathe somewhat like human beings. They take in oxygen and give off carbonic-acid gas. The air enters the tree through the leaves and small openings in the bark, which are easily seen in such trees as the cherry and birch. Trees breathe constantly, but they digest and a.s.similate food only during the day and in the presence of light. In the process of digestion and a.s.similation they give off oxygen in abundance, but they retain most of the carbonic acid gas, which is a plant food, and whatever part of it is not used immediately is stored up by the tree and used for its growth and development. Trees also give off their excess moisture through the leaves and bark. Otherwise they would become waterlogged during periods when the water is rising rapidly from the roots.
After the first year, trees grow by increasing the thickness of the older buds. Increase in height and density of crown cover is due to the development of the younger twigs. New growth on the tree is spread evenly between the wood and bark over the entire body of the plant. This process of wood production resembles a factory enterprise in which three layers of material are engaged.
In the first two of these delicate tissues the wood is actually made. The inner side of the middle layer produces new wood while the outer side grows bark. The third layer is responsible for the production of the tough, outer bark. Year after year new layers of wood are formed around the first layers. This first layer finally develops into heartwood, which, so far as growth is concerned, is dead material. Its cells are blocked up and prevent the flow of sap. It aids in supporting the tree. The living sapwood surrounds the heartwood. Each year one ring of this sapwood develops. This process of growth may continue until the annual layers amount to 50 or 100, or more, according to the life of the tree.
One can tell the age of a tree by counting the number of annual rings. Sometimes, because of the interruption of normal growth, two false rings may be produced instead of a single true ring.
However, such blemishes are easy for the trained eye to recognize. Heartwood does not occur in all varieties of trees. In some cases, where both heartwood and sapwood appear, it is difficult to distinguish between them as their colors are so nearly alike. Because it takes up so much moisture and plant food, sapwood rots much more quickly than heartwood. The sapwood really acts as a pipe line to carry water from the roots to the top of the tree. In some of our largest trees the moisture is raised as high as 300 feet or more through the sapwood.
Strange though it may seem, trees fight with each other for a place in the sunlight. Sprightly trees that shoot skyward at a swift pace are the ones that develop into the monarchs of the forest. They excel their mates in growth because at all times they are exposed to plenty of light. The less fortunate trees, that are more stocky and st.u.r.dy, and less speedy in their climb toward the sky, are killed out in large numbers each year. The weaker, spindly trees of the forest, which are slow growers, often are smothered out by the more vigorous trees.
Some trees are able to grow in the shade. They develop near or under the large trees of the forest. When the giants of the woodland die, these smaller trees, which previously were shaded, develop rapidly as a result of their freedom from suppression. In many cases they grow almost as large and high as the huge trees that they replace. In our eastern forests the hemlock often follows the white pine in this way. Spruce trees may live for many years in dense shade. Then finally, when they have access to plenty of light they may develop into st.u.r.dy trees. A tree that is a pigmy in one locality may rank as a giant in another region due to different conditions of growth and climate. For example, the canoe birch at its northern limit is a runt. It never grows higher than a few feet above the ground. Under the most favorable conditions in Florida, where this species thrives, such trees often tower to a height of 125 feet.
In sheltered regions the seeds of trees may fall, sprout and take root close to their parent trees. As a rule, the wind plays a prominent part in distributing seed in every section of the country. Pine and fir seeds are equipped with wings like those of a bird or an airplane. They enable the seeds to fly long distances on the wind before they drop to the ground and are covered with leaves. Maple seeds fly by means of double-winged sails which carry them far afield before they settle. Ash seeds have peculiar appendages which act like a skate-sail in transporting them to distant sections. Cottonwood seeds have downy wings which aid their flight, while ba.s.swood seeds are distributed over the country by means of parachute-like wings.
The pods of the locust tree fall on the frozen ground or snow crust and are blown long distances from their source. On the other hand, oak, hickory, and chestnut trees produce heavy seeds which generally remain where they fall.
Squirrels are the most industrious foresters in the animal world.
Each year they bury great quant.i.ties of tree seeds in h.o.a.rds or caches hidden away in hollow logs or in the moss and leaves of the forest floor. Birds also scatter tree seed here, there, and everywhere over the forests and the surrounding country. Running streams and rivers carry seeds uninjured for many miles and finally deposit them in places where they sprout and grow into trees. Many seeds are carried by the ocean currents to distant foreign sh.o.r.es.
The decay of leaves and woodland vegetation forms rich and fertile soils in the forests, in which conditions are favorable for the development of new tree growth. When living tree seeds are exposed to proper amounts of moisture, warmth and air in a fertile soil, they will sprout and grow. A root develops which pushes its way down into the soil, while the leaf-bud of the plant, which springs from the other end of the seed, works its way upward toward the light and air. This leafy part of the seed finally forms the stem of the tree. But trees may produce plenty of seed and yet fail to maintain their proper proportion in the forest. This results because much of the seed is unsound. Even where a satisfactory supply of sound fertile seed is produced, it does not follow that the trees of that variety will be maintained in the forest, as the seed supply may be scattered in unfavorable positions for germination. Millions of little seedlings, however, start to grow in the forest each year, but only a small number survive and become large trees. This is because so many of the seedlings are destroyed by forest fires, cattle and sheep grazing, unfavorable soil and weather conditions, and many other causes.
Beech and chestnut trees and others of the broad-leaved type reproduce by means of sprouts as well as by seed. Generally, the young stumps of broad-leaved trees produce more sprouts than the stumps of older trees which have stood for some time. Among the cone-bearing trees reproduction by sprouts is rare. The redwood of California is one of the few exceptions. The pitch pine of the Eastern States produces many sprouts, few of which live and develop into marketable timber.
When trees are grown in nurseries, the practice is to sow the seed in special beds filled with rich soil. Lath screens are used as shade. They protect the young seedlings from the sun just as the parent trees would do in the forest. The seedbeds are kept well cultivated and free of weeds so that the seedlings may have the best opportunities for rapid growth. Generally the seeds are sown in the spring between March and May. Such seeds as the elms and soft maples, which ripen in the early summer, are sown as soon as possible after they are gathered. Practical tests have shown that thick sowings of tree seeds give the best results.
There is little danger of weeds smothering out the seedlings under such conditions. After the seed has germinated the beds may be thinned so that the seedlings will have more room to develop.
During the fall of the same year, or in the following spring, the seedlings should be transplanted to nursery rows. Thereafter it is customary to transplant the young trees at least once again during damp weather. When the trees finally are robust and vigorous and have reached the age of two to five years, they are dug up carefully and set out permanently. The usual practice is to keep the seedlings one year in the seedbed and two years in the nursery rows before they are set out. Whether the transplanting should take place during the spring or fall depends largely on the climate and geography of the locality. Practical experience is the best guide in such matters.
Some farmers and land owners are now interested in setting out hardwood forests for commercial purposes. If they do not wish to purchase their seedlings from a reliable nursery-man, they can grow them from carefully selected seed planted in well-prepared seedbeds. The popular practice is to sow the seed in drills about 2 to 3 feet apart so that horses may be used for cultivation. The seeds are sown to a depth of 2 to 3 times their thickness. They are placed close enough in the drill so that from 12 to 15 seedlings to the linear foot result. In order to hasten the sprouting of the seeds, some planters soak them in cold water for several days before sowing. In the case of such hard-coated seed as the black locust or honey locust, it is best to soak them in hot water before planting.
CHAPTER II
THE FOREST FAMILIES
Trees are as queer in picking out places to live and in their habits of growth as are the peoples of the various races which inhabit the world. Some trees do best in the icy northland. They become weak and die when brought to warm climates. Others that are accustomed to tropical weather fail to make further growth when exposed to extreme cold. The appearance of Jack Frost means death to most of the trees that come from near the equator. Even on the opposite slopes of the same mountain the types of trees are often very different. Trees that do well on the north side require plenty of moisture and cool weather. Those that prosper on south exposures are equipped to resist late and early frosts as well as very hot sunshine. The moisture needs of different trees are as remarkable as their likes and dislikes for warmth and cold. Some trees attain large size in a swampy country. Trees of the same kind will become stunted in sections where dry weather persists.
In some parts of the United States forestry experts can tell where they are by the local tree growth. For example, in the extreme northern districts the spruce and the balsam fir are native. As one travels farther south these give way to little Jack pine and aspen trees. Next come the stately forests of white and Norway pine. Sometimes a few slow-growing hemlock trees appear in the colder sections. If one continues his journey toward the equator he will next pa.s.s through forests of broad-leaved trees. They will include oak, maple, beech, chestnut, hickory, and sycamore.
In Kentucky, which is a centre of the broad-leaved belt, there are several hundred different varieties of trees. Farther south, the cone-bearing species prevail. They are followed in the march toward the Gulf of Mexico by the tropical trees of southern Florida. If one journeys west from the Mississippi River across the Great Plains he finally will come to the Rocky Mountains, where evergreen trees predominate. If oak, maple, poplar, or other broad-leaved trees grow in that region, they occur in scattered stands. In the eastern forests the trees are close together. They form a leafy canopy overhead. In the forests of the Rockies the evergreens stand some distance apart so that their tops do not touch. As a result, these Western forests do not shade the ground as well as those in the east. This causes the soils of these forests to be much drier, and also increases the danger from fire.
The forests of western Washington and Oregon, unlike most timberlands of the Rocky Mountain Region, are as dense as any forests in the world. Even at midday it is as dark as twilight in these forests. The trees are gigantic. They tower 150 to 300 feet above the ground. Their trunks often are 6 feet or larger in diameter. They make the trees of the eastern forests look stunted. They are excelled in size only by the mammoth redwood trees of northern California and the giant Sequoias of the southern Sierras.
[Ill.u.s.tration: THE SEQUOIAS OF CALIFORNIA]
Differences of climate have largely influenced tree growth and types in this country. The distribution of tree families is changing all the time. It shifts just as the climate and other conditions change. Trees constantly strive among themselves for control of different localities. For a time one species will predominate. Then other varieties will appear and displace the ones already established. The distribution of trees changes very remarkably from one century to another. For example, in some sections, the red and black oaks are replacing the white oaks.
Some trees are light-lovers. They require much more sunlight than others that do well under heavy shade. Oak trees require plenty of light; maples or beeches thrive on little light.
The seed of trees requiring little light may be scattered in a dense forest together with that of trees which need plenty of daylight in order to make normal growth. The seedlings that like shade will develop under such conditions while those that need light will pine away and die. Gradually the shade-loving trees will replace the light-loving trees in such a forest stand. Even the different trees of the same family often strive with one another for light and moisture. Each tree differs from every other one in shape and size. Trees will adapt themselves to the light and moisture conditions to which they are exposed. A tree that has access to plenty of moisture and sunlight grows evenly from the ground to its top with a bushy, wide-spreading crown.
The same tree, if it grows in the shade, will reach a greater height but will have a small compact crown. Trees run a race in their rapidity of growth. The winners get the desirable places in the sunlight and prosper. The losers develop into stunted trees that often die, due to lack of light exposure. A better quality of lumber results from tall straight trees than that produced by the symmetrical, branching trees. That is why every forester who sets out trees tries to provide conditions which will make them grow tall and with the smallest possible covering of branches on the lower part of the trunks.
Where trees are exposed to strong winds, they develop deep and strong root systems. They produce large and strong trunks that can bend and resist violent winds which sway and twist them in every direction. Such trees are much stronger and st.u.r.dier than those that grow in a sheltered forest. The trees that are blown down in the forest provide s.p.a.ce for the introduction and growth of new varieties. These activities are constantly changing the type of tree growth in the forest.
Our original forests which bordered the Atlantic coast line when America was first settled, were dense and impenetrable. The colonists feared the forests because they sheltered the hostile Indians who lurked near the white settlements. In time this fear of the forest developed into hatred of the forest. As a result, the colonists cut trees as rapidly as they could. In every way they fought back the wilderness. They and their children"s children have worked so effectively that the original wealth of woodlands has been depleted. At present, cleared fields and cutover areas abound in regions that at one time were covered with magnificent stands of timber.
In many sections of the country our forests are now so reduced that they are of little commercial importance. However, these areas are not yet entirely denuded. Predictions have been made frequently that our woodlands would soon disappear. Scientific foresters report that such statements are incorrect. There are only a few districts in the country which probably will never again support much tree growth. Their denuded condition is due largely to the destruction of the neighboring mountain forests and to the activities of erosion. Under ordinary conditions, natural reforestation will maintain a satisfactory tree growth on lands where a practical system of forest protection is practiced.
The complete removal of the forest is now accomplished only in fertile farming regions, where the agricultural value of the land is too high to permit it to remain longer in forest cover.
Even in the Mississippi Valley and the Great Lakes belts there are still large areas of forest land. Most of the farms have woodlots which provide fuel, fencing, and some lumber. For the most part, these farm woodlots are abused. They have not been managed correctly. Fortunately, a change for the better is now evident. The farm woodlot owners are coming to appreciate the importance of protecting the trees for future use. In some cases, they are even replanting areas that have been cut over. There are large tracts of sandy, rocky and swampy land in these districts that are satisfactory for tree production. In fact, about all these fields are good for is the growing of timber. Campaigns are now under way to increase tree planting and develop the production of lands adapted for forestry which previously have been idle.
The United States of the future will not be a desert, tree-less country. However, immediate measures to save our remaining trees must be developed. The greater part of our virgin timber has already been felled. The aftermath forests, which succeed the virgin stand, generally are inferior. Our supplies of ash, black walnut and hickory, once abundant, are now seriously limited.
Formerly, these mixed forests covered vast stretches of country which today support only a scant crop of young trees which will not be ready for market for many years. These second-growth stands will never approach in value or quality the original forests. Over large areas, poplar, white birch, and Jack pine trees now predominate on lands which formerly bore dense stands of white pine. In many places, scrubby underbrush and stunted trees occupy lands which heretofore have been heavy producers of marketable timber trees.
Generally speaking, farm lands should not be used for forestry purposes. On the other hand, some forest lands can be profitably cleared and used for agriculture. For example, settlers are felling trees and fighting stumps in northern Wisconsin, Michigan, and Minnesota. Some of these virgin lands are valuable for farming purposes, others are not. It is preferable that they should produce farm crops instead of tree crops if the land is best adapted to agricultural use. It is an economic necessity that all lands in this country best suited for farming purposes should be tilled. Our ever-increasing population demands that every acre of land useful for growing crops should be cleared and devoted to farming. Under such conditions, the settlers should reserve sufficient woodlands for their home needs, carefully distinguishing between the land that is best for agricultural purposes and the land that is best for forestry purposes, and thus doubling their resources.
Thoughtless lumbermen have pillaged millions of acres of our most productive forests. The early lumbermen wasted our woodland resources. They made the same mistakes as everyone else in the care and protection of our original forests. The greatest blame for the wasting of our lumber resources rests with the State and Federal authorities who permitted the depletion. Many of our lumbermen now appreciate the need of preserving and protecting our forests for future generations. Some of them have changed their policies and are now doing all in their power to aid forest conservation.
The ability of a properly managed forest to produce new crops of trees year after year promises us a future supply of wood sufficient for all our needs if only we will conserve our timberlands as they deserve. It is our duty to handle the forests in the same way that fertile farming fields are managed.