Tools Used in Draining
Levelling.—In the carrying out of drainage operations in connexion with the formation of new plantations, but particularly where the land is nearly level, one of the most necessary implements is the spirit-level or theodolite. There are many other operations, as well as in connexion with draining, where the level and the knowledge of its working are all-important for the forester. Thus in the formation of roads and paths, levelling of ground inequalities, lake and pond forming, etc., the level will be found an almost indispensable instrument—in fact, it cannot well be done without.
Of levelling instruments there are various descriptions, but the simplest of any is the ordinary spirit-level, it being cheap, easily carried about in the pocket, and when erected on a temporary staff will fall in with most requirements in connexion with general forest work. The illustration (Fig. 1) will give a good idea of the simple instrument. When in use the spirit-level is fixed in a frame of brass, the whole being screwed into a staff or support, e. The brass screw, d, serves to adjust the level as required.
There are two eyesights, a and b, the latter being a square opening, with a fine hair wire crossing it in the middle.
The relative heights of a series of points are obtained by means of their vertical distances from others which, on the supposition of the earth being a sphere, are equally distant from its centre, and these, which are called level-points, must be found by an instrument constructed for the purpose—spirit-level, theodolite, etc. Generally choice is made of any convenient stations, a, b, c, d, on the line of operation (see Fig. 2), and the distances between them are determined by actual ad-measurement. The instrument is then set up and adjusted at, or near, the middle of the interval between every two such points in succession. When the level thus placed, as at f, has been rendered horizontal by means of the adjusting screw, an assistant at each of the stations a and b, holding what is called a station-staff in a vertical position, moves an index along the staff, up or down, as dictated by the observer of the level, till it coincides with the intersecting wire as seen in the eyesight or telescope. The points thus determined on the stave are represented by e and g, and these are termed level-points, or points equally distant from the centre of the earth. Therefore the heights a, e, and b, g, being read on the graduated staves, the difference between them will give the relative heights of the ground at a and b. Similar processes are repeated with respect to the points b and c, and c and d, the instrument being placed at i and m, midway between them. Usually the heights b g, c l and d n are inserted in a column headed “Foresights,” and the heights a e, b h, c k and d n in a collateral column headed “Backsights.” The difference between the sums of the numbers in these two columns will be equal to the height of one extremity (a) of the line, above the other (d). When a number of levels have to be taken in succession, it will be found a saving of time to use the surveyor’s level or theodolite instead of the ordinary spirit-level illustrated.
With regard to the use of the instrument as shown in Fig. 1, it may be necessary to state that the height of the eyesight b from the ground must be deducted from the point observed. As an example: if the object-pole or staff be marked in feet or inches, and the hair wire in taking a sight strike the same at, say, 8 ft., then, if the eyesight be 4 ft. from the ground, the difference of level between the two stations (instrument and station) will be 4 ft., that is, there will be 4 ft. of a fall from the spirit-level station to that of the station where the staff was placed. On the other hand, should the hair wire strike the object-pole at, say, 2 ft. from the ground, these 2 ft. must be deducted from the height of the eyesight, which, as we have said, was 4 ft., then the ground at the station-pole must be 2 ft. higher than that at the spirit-level.
Clearing the Ground.—Coarse-growing herbage, which often includes heath, gorse, and rough grasses, that would interfere with planting operations, should be removed, but not indiscriminately, as it may prove of inestimable value under certain conditions. On exposed and high-lying ground, the heath and grasses will prove of great advantage to the young trees, and usually they are not too luxuriant or apt to cause damage at high altitudes. Where, however, the growth of such shrubs or grasses would be detrimental to the young trees, by all means have them removed. The best way is either to cut them over or grub out by the root, and burn on the ground. During a continuance of dry weather it may be possible to burn without either cutting or uprooting, but, generally speaking, removal of the roots is to be encouraged.
Pitting.—The advantages of pitting over any method of planting cannot be questioned, and this is particularly the case with ground that has hitherto been uncultivated. Compared with notch planting, this system is, no doubt, more expensive, but that the future benefits to the plants are greatly enhanced is admitted by all practical arboriculturists.
It is not, however, to be inferred that, though pitting is preferable, notching is to be abandoned, for there are many precipitous, rocky places where it would be the only practice feasible, and plants so inserted have often succeeded admirably.
The pits should in all cases be opened for some time before planting—indeed, in unfavourable soils and situations, it is a good practice to have such work performed in autumn and the plants inserted the following spring. By so doing, the earth that has been removed from the pits will lie fully exposed to the mellowing influences of frost and sunshine, so that when the time for replacing it comes round, it will be in the best possible condition for applying to the roots of the young trees.
The pits in uncultivated lands should be made circular, about 18 in. in diameter and fully 12 in. deep, and the sides and bottom well loosened up with a pick. In loose or recently cultivated soil the pits may be much smaller. Take off the surface turf in halves, placing these on one side of the pit, and the soil on the other, for ease and convenience in planting. When the ground slopes quickly the soil removed from the pits should, so as to facilitate quick replacing, be deposited on the higher side.
Planting.—This may be successfully carried out during all open weather from about the end of September to the beginning of April, but, generally speaking, autumn planting is to be recommended. There are several exceptions however: such as when we have to deal with peat bog, water-logged soil, exposed hillsides, or land by the sea-coast. Where the newly-inserted plants have to cope with prolonged storms, such as we get on hillsides or by the sea, or contend with very uncongenial soils, it is always a wise policy to defer planting until spring, or just when the trees are about to make a start to growth, as they, with their freshness and vigour undiminished by the change from the nursery border to the more trying surroundings just referred to, are more likely to take hold at once and succeed.
The battering and swaying that autumn planted trees receive when exposed to the hurricanes of our hillsides or seaside sites so enfeeble them that, in spring, when growth should commence, the majority will be found to be in a very unsatisfactory state, whereas, by inserting in spring, when growth will soon be at its full activity, the chances of succeeding are greatly enhanced. In peat bog the antiseptic properties of the soil act dangerously on the roots of young trees if allowed to remain therein for some time before active growth has commenced. However, with the exceptions cited, tree planting throughout the British Isles generally should be taken in hand as soon as the leaves of the hardwood species have fallen, which usually takes place about the second or third week of October, much depending on the particular season. Lift the plants very carefully from the nursery brakes, and do not, on any account, tolerate the too-often-enacted practice of tearing the trees from the ground, and before they have been properly loosened on both sides of the lines with a fork. To lift nursery stock properly—and the extra expense incurred in so doing is money well spent—a trench should be thrown out along each side of the line and the soil undermined from beneath the roots, so that the plants can be lifted without tearing or straining the tender rootlets. It is not important, if the plants are inserted soon after being lifted, that soil should accompany each, the roots being plentiful and unmutilated making up for the want of this. Where, however, the plants have not to be conveyed far from the home nursery to the plantation there is no need to remove much of the soil, for if left intact the young tree is far more likely to start away freely into growth than if this was shaken clean off.