Factors Affecting Tending Operation Thinning Practices
The following factors are important for deciding the adoption of thinning practice.
i) Nature of Species:
Light demanders are less tolerant of crowding than shade bearers and therefore, frequent thinning is required to remove competition in light demander species.
In young age, when the crown formation has not completed, mechanical thinning or stick thinning by some numerical formula is carried out with success.
iii) Site Quality:
On poor sites, heavy thinning is not recommended because the rate of growth on such sites is poor and the heavy openings may not be occupied.
iv) Improvements in Felling:
Improvement felling has been defined as per removal of less valuable trees in a crop with the interest of better growth of the more valuable individuals, usually applied to a mixed, uneven aged forest. It may include thinning of closely stoked groups along with clearing and general assistance to young growth of valuable species.
Pruning is defined as the elimination of branches in order to obtain trees with clean bole. The elimination of branches by physical and biotic agencies of the environment is called Natural pruning. Removal of branches from the selected portions of the tree by mechanical means is referred as artificial pruning. Pruning occurs naturally when the crop is dense enough particularly in younger stage. The process of natural pruning completes in three stages namely:
i) Killing of branches,
ii) Shedding of dead branches and
iii) Halting over of the entire branch stub
Killing of the branches is determined by the density of the crop. The lower branches of trees usually die when crows of the adjacent trees are close to each other. Death in such cases occurs below the point of closer. The shading of branches occurs after the dead branches are attacked by saprophytic fungi, insects, etc. are broken away by winds etc. The shading of dead branches from the main stem is followed by the occlusion of the short stubs produced by the dead branches. Natural pruning can be accelerated by manipulation of the density and composition of the crop. The rate of killing of lower branches, their shedding and healing of the branch stub depends on species and their habitat factors. The retention of under story trees may also lead to effective natural pruning. The simplest method of obtaining natural pruning is to develop and maintain dense stocking in the main crop. This may decrease the rate of diameter increment. Therefore, it is necessary to reduce the crop density as soon as natural pruning is achieved.
Artificial pruning results in production of clear boled trees on shorter rotation than would be required in natural pruning. Plantation cannot be raised in closer spacing because it leads to higher investment and therefore artificial pruning, sometimes may be necessary.
In the artificial pruning, the moribund and lower green branches are cut off from the main stem as near to the bole as possible. The use of handsaw has been found useful than bladed instruments. A small ladder is also necessary. Except in certain cases e.g. poplar, mulberry, artificial pruning on large scale has yet to be adopted in India. The height up to which pruning should be carried out artificially depends upon species, age and local conditions. In young plantations it should be carried out up to one half to three fifth of the total height of the tree. The object of pruning is to obtain knot free timber and it is likely to be obtained more effectively by the removal of lateral buds.
vi) Climber Cutting:
Climber cutting should be done along with the tending operations as well as while carrying out markings for felling in the forest. Climbers are particularly harmful when the trees are young. In older trees, they constrict the stem and deteriorate the value of wood.
The climber cutting should be done at the base and one meter above and the piece should be removed in order to ensure that climber has been cut. A more effective method for the control of climber is to dig up tubers during the rains. The climbers should be cut preferably during monsoon.