Studies of Trees Part 21

Improvement by cutting: The removal of certain trees in a grove is often necessary to improve the quality of the better trees, increase their growth, make the place accessible, and enhance its beauty. Cutting in a wooded area should be confined to suppressed trees, dead and dying trees and trees badly infested with insects and disease. In case of farm woodlands, mature trees of market value may be cut, but in parks and on private estates these have a greater value when left standing. The cutting should leave a clean stand of well-selected specimens which will thrive under the favorable influence of more light and growing s.p.a.ce. Considerable care is required to prevent injury to the young trees when the older specimens are cut and hauled out of the woods. The marking of the trees to be removed can best be done in summer when the dead and live trees can be distinguished with ease and when the requisite growing s.p.a.ce for each tree can be judged better from the density of the crowns. The cutting, however, can be done most advantageously in winter.

Immediately after cutting all diseased and infested wood should be destroyed. The sound wood may be utilized for various purposes. The bigger logs may be sold to the local lumber dealers and the smaller material may be used for firewood. The remaining brush should be withdrawn from the woodlot to prevent fire during the dry summer months.

In marking trees for removal, a number of considerations are to be borne in mind besides the elimination of dead, diseased and suppressed trees. When the marker is working among crowding trees of equal height, he should save those that are most likely to grow into fine specimen trees and cut out all those that interfere with them.

The selection must also favor trees which are best adapted to the local soil and climatic conditions and those which will add to the beauty of the place. In this respect the method of marking will be different from that used in commercial forestry, where the aim is to net the greatest profit from the timber. In pure forestry practice, one sees no value in such species as dogwood, ironwood, juneberry, sumac and sa.s.safras, and will therefore never allow those to grow up in abundance and crowd out other trees of a higher market value. But on private estates and in park woodlands where beauty is an important consideration, such species add wonderful color and attractiveness to the forest scene, especially along the roads and paths, and should be favored as much as the other hardier trees. One must not mark too severely in one spot or the soil will be dried out from exposure to sun and wind. When the gaps between the trees are too large, the trees will grow more slowly and the trunks will become covered with numerous shoots or suckers which deprive the crowns of their necessary food and cause them to "die back." Where the trees are tall and slim or on short and steep hillsides, it is also important to be conservative in marking in order that the stand may not be exposed to the dangers of windfall. No hard-and-fast rule can be laid down as to what would const.i.tute a conservative percentage of trees to cut down. This depends entirely on the local conditions and on the exposure of the woodlot. But in general it is not well to remove more than twenty per cent of the stand nor to repeat the cutting on the same spot oftener than once in five or six years. The first cutting will, of course, be the heaviest and all subsequent cuttings will become lighter and lighter until the woodlot is put in good growing condition. On private estates and parks, where beauty is the chief aim, the woodland should be kept as natural, informal and as thick as possible. Where the woodland is cut up by many paths and drives, density of vegetation will add to the impression of depth and distance.

Protection: This subject has already been discussed considerably in the previous study on Forestry, and here it becomes necessary merely to add a few suggestions with special reference to private and park woodlands.

Guarding woodlands from _fire_ is the most important form of protection. Surface fires are very common on small woodland holdings and the damage done to the standing vegetation is generally underestimated. An ordinary ground or surface fire on a woodland area will burn up the leaf-litter and vegetable mold, upon which the trees depend so much for food and moisture, and will destroy the young seedlings on the ground. Where the fire is a little more severe, the older trees are badly wounded and weakened and the younger trees are frequently killed outright. Insects and disease find these trees an easy prey, and all related forest conditions commence to deteriorate.

Constant watchfulness and readiness to meet any emergency are the keynote of effective fire protection. Notices similar to the one shown in Fig. 143 often help to prevent fires. It is also helpful to inst.i.tute strict rules against dropping lighted matches or tobacco, or burning brush when the ground is very dry, or leaving smouldering wood without waiting to see that the fire is completely out. There should be many roads and foot-paths winding through the woodland in order that they may serve as checks or "fire lanes" in time of fire.

These roads and paths should be kept free from brush and leaves and should be frequently patrolled. When made not too wide, unpretentious and in conformity with the natural surroundings, such drives and paths can become a very interesting feature of the place, winding through the woodland, exposing its charms and affording opportunity for pleasant driving and walking. The borders of the paths can be given special attention by placing the more beautiful native shrubs in prominent positions where they can lend increased attractiveness.

In case of fire, it should be possible to call for aid by telephone directly from the woodland and to find within easy reach the tools necessary to combat fire. It is also important to obtain the co-operation of one's neighbors in protecting the adjoining woodlands, because the dangers from insects, disease and fire threatening one bit of woodland area are more or less dependent upon the conditions in the adjoining woodland.

[Ill.u.s.tration: FIG. 143.--Poster Suitable for Private Woodlands and Forest Parks. The translations in Italian and Polish have been used by the writer in this particular instance to meet the local needs.]

As to other forms of protection, pa.s.sing mention may be made of the importance of keeping out cattle, sheep and hogs from the woods, of eliminating all insects and disease, of keeping the ground free from brush and other inflammable material, of retaining on the ground all fallen leaves and keeping the forest well stocked with little trees and shrubs.

Forest lands may be exempted from taxation: In New York and other States there exists a State law providing for exemption or reduction in taxes upon lands which are planted with forest trees or maintained as wooded areas. The object of the law is to encourage home forestry and to establish fairness in the agricultural land-tax law by placing forest lands in the same category with other crop-producing lands. For detailed information and a copy of the law, one should address the local State Forestry Commission.

CHAPTER VIII

OUR COMMON WOODS: THEIR IDENTIFICATION, PROPERTIES AND USES

Woods have different values for various practical purposes because of their peculiarities in structure. A knowledge of the structural parts of wood is therefore necessary as a means of recognizing the wood and of determining why one piece is stronger, heavier, tougher, or better adapted for a given service than another.

Structure of wood: If one examines a cross-section of the bole of a tree, he will note that it is composed of several distinct parts, as shown in Fig. 145. At the very center is a small core of soft tissue known as the _pith_. It is of much the same structure as the pith of cornstalk or elder, with which all are familiar. At the outside is the _bark_, which forms a protective covering over the entire woody system. In any but the younger stems, the bark is composed of an inner, live layer, and an outer or dead portion.

Between the pith at the center and the bark at the outside is the wood. It will be noted that the portion next to the bark is white or yellowish in color. This is the _sapwood_. It is princ.i.p.ally through the sapwood that the water taken in by the roots is carried up to the leaves. In some cases the sapwood is very thin and in others it is very thick, depending partly on the kind of tree, and partly on its age and vigor. The more leaves on a tree the more sapwood it must have to supply them with moisture.

[Ill.u.s.tration: FIG. 144.--Pine Wood. (Magnified 30 times.)]

Very young trees are all sapwood, but, as they get older, part of the wood is no longer needed to carry sap and it becomes _heartwood_. Heartwood is darker than the sapwood, sometimes only slightly, but in other instances it may vary from a light-brown color to jet black. It tends to fill with gums, resins, pigments and other substances, but otherwise its structure is the same as that of the sapwood.

[Ill.u.s.tration: FIG. 145.--Cross-section of Oak.]

The wood of all our common trees is produced by a thin layer of cells just beneath the bark, the _cambium_. The cambium adds new wood on the outside of that previously formed and new bark on the inside of the old bark. A tree grows most rapidly in the spring, and the wood formed at that time is much lighter, softer and more porous than that formed later in the season, which is usually quite hard and dense. These two portions, known as _early wood_ or spring wood, and _late wood_ or summer wood, together make up one year's growth and are for that reason called _annual rings_. Trees such as palms and yucca do not grow in this way, but their wood is not important enough in this country to warrant a description.

[Ill.u.s.tration: FIG. 146.--White Oak Wood. (Magnified 20 times.)]

If the end of a piece of oak wood is examined, a number of lines will be seen radiating out toward the bark like the spokes in a wheel. These are the _medullary rays_. They are present in all woods, but only in a few species are they very prominent to the unaided eye. These rays produce the "flakes" or "mirrors" that make quartersawed (radially cut) wood so beautiful. They are thin plates or sheets of cells lying in between the other wood cells. They extend out into the inner bark.

While much may be seen with the unaided eye, better results can be secured by the use of a good magnifying gla.s.s. The end of the wood should be smoothed off with a very sharp knife; a dull one will tear and break the cells so that the structure becomes obscured.

With any good hand lens a great many details will then appear which before were not visible. In the case of some woods like oak, ash, and chestnut, it will be found that the early wood contains many comparatively large openings, called _pores_, as shown in Figs. 146 and 147. Pores are cross-sections of vessels which are little tube-like elements running throughout the tree. The vessels are water carriers. A wood with its large pores collected into one row or in a single band is said to be _ring-porous_. Fig. 146 shows such an arrangement. A wood with its pores scattered throughout the year's growth instead of collected in a ring is _diffuse-porous_.

Maple, as shown in Fig. 152, is of this character.

[Ill.u.s.tration: FIG. 147.--Example of the Black Oak Group. (Quercus coccinea.) (Magnified 20 times.)]

All of our broadleaf woods are either ring-porous or diffuse-porous, though some of them, like the walnut, are nearly half way between the two groups.

If the wood of hickory, for example, be examined with the magnifying lens, it will be seen that there are numerous small pores in the late wood, while running parallel with the annual rings are little white lines such as are shown in Fig. 149. These are lines of _wood parenchyma_. Wood parenchyma is found in all woods, arranged sometimes in tangential lines, sometimes surrounding the pores and sometimes distributed over the cross-section. The dark, horn-like portions of hickory and oak are the _woodfibers_. They give the strength to wood.

In many of the diffuse-porous woods, the pores are too small to be seen with the unaided eye, and in some cases they are not very distinct even when viewed with a magnifier. It is necessary to study such examples closely in order not to confuse them with the woods of conifers.

The woods of conifers are quite different in structure from broadleaf woods, though the difference may not always stand out prominently. Coniferous woods have no pores, their rays are always narrow and inconspicuous, and wood parenchyma is never prominent.

The woods of the pines, spruces, larches, and Douglas fir differ from those of the other conifers in having _resin ducts_, Fig. 144.

In pines these are readily visible to the naked eye, appearing as resinous dots on cross-sections and as pin scratches or dark lines on longitudinal surfaces. The presence or absence of resin ducts is a very important feature in identifying woods, hence it is very important to make a careful search for them when they are not readily visible.

How to identify a specimen of wood: The first thing to do in identifying a piece of wood is to cut a smooth section at the end and note (without the magnifier) the color, the prominence of the rays and pores, and any other striking features. If the pores are readily visible, the wood is from a broadleaf tree; if the large pores are collected in a ring it belongs to the ring-porous division of the broadleaf woods. If the rays are quite conspicuous and the wood is hard and heavy, it is oak, as the key given later will show. Close attention to the details of the key will enable one to decide to what group of oaks it belongs.

In most cases the structure will not stand out so prominently as in oak, so that it is necessary to make a careful study with the hand lens. If pores appear, their arrangement, both in the early wood and in the late wood, should be carefully noted; also whether the pores are open or filled with a froth-like substance known as _tyloses_.

Wood parenchyma lines should be looked for, and if present, the arrangement of the lines should be noted.

[Ill.u.s.tration: FIG. 148.--(Magnified about 8 times.)]

If no pores appear under the magnifying lens, look closely for resin ducts. If these are found, note whether they are large or small, numerous or scattered, open or closed, lighter or darker than the wood. Note also whether the late wood is very heavy and hard, showing a decided contrast to the early wood, or fairly soft and grading into the early wood without abrupt change. Weigh the piece in your hand, smell a fresh-cut surface to detect the odor, if any, and taste a chip to see if anything characteristic is discoverable.

Then turn to the following key:

KEY

I. WOODS WITHOUT PORES--CONIFERS OR SO-CALLED "SOFTWOODS"

A. Woods with resin ducts.

1. Pines. Fig. 144. Resin ducts numerous, prominent, fairly evenly distributed. Wood often pitchy. Resinous odor distinct. Clear demarcation between heart and sapwood. There are two groups of pines--soft and hard.

(a) Soft Pines. Wood light, soft, not strong, even-textured, very easy to work. Change from early wood to late wood is gradual and the difference in density is not great.

(b) Hard Pines. Wood variable but typically rather heavy, hard and strong, uneven textured, fairly easy to work. Change from early wood to late wood is abrupt and the difference in density and color is very marked, consequently alternate layers of light and dark wood show. The wood of nearly all pines is very extensively employed in construction work and in general carpentry.

2. Douglas fir. Resin ducts less numerous and conspicuous than in the pines, irregularly distributed, often in small groups. Odorless or nearly so. Heartwood and sapwood distinct. The wood is of two kinds.

In one the growth rings are narrow and the wood is rather light and soft, easy to work, reddish yellow in color; in the other the growth rings are wide, the wood is rather hard to work, as there is great contrast between the weak early wood and the very dense late wood of the annual rings.

Douglas fir is a tree of great economic importance on the Pacific Coast. The wood is much like hard pine both in its appearance and its uses.

3. Spruces. Resin ducts few, small, unevenly distributed; appearing mostly as white dots. Wood not resinous; odorless. The wood is white or very light colored with a silky l.u.s.ter and with little contrast between heart and sapwood. It is a great deal like soft pine, though lighter in color and with much fewer and smaller resin ducts. The wood is used for construction, carpentry, oars, sounding boards for musical instruments, and paper pulp.

4. Tamarack. Resin ducts the same as in the spruces. The color of the heartwood is yellowish or russet brown; that of the distinct sapwood much lighter. The wood is considerably like hard pine, but lacks the resinous odor and the resin ducts are much fewer and smaller.