Method of Tending Operation – Thinning
Following Methods of Thinning can be Adopted:
1) Mechanical Thinning,
2) Ordinary Thinning,
3) Crown Thinning,
4) Free Thinning,
5) Crab’s Advance Thinning,
6) Numerical Thinning
1) Mechanical Thinning:
This type of thinning is usually applied in young crops or young plantations before the crown differentiation has taken place. In teak plantations of Kerala, first and second thinning carried out at the age of 4 and 8 years are usually mechanical thinning and consists of the removal of alternate diagonal lines or rows of trees reducing the stocking from 2,500 trees per ha to 1250 trees per ha after the first mechanical thinning and then to 625 trees per hectare after second thinning with spacing 2 in x 2 in to about 2.85 in x 2.85 in and then ultimately to 4 in x 4 in after second thinning.
2) Ordinary Thinning:
This is called as "Low Thinning". In ordinary thinning, the trees are removed from lower crown classes. Ordinary thinning has been devised to follow the nature i.e. those trees, which have been unsuccessful in the struggle of existence, are removed first. Ordinary thinning is the most commonly used thinning practice in forestry. It is most for light demander species. This method of thinning is useful and may be economically applied in species and areas where small size timber has a market.
The method is simple in execution. Removal of lower crown classes suitable for area where there is no danger of soil deterioration. Forests infested with climbers and where there is risk of crown fire. Ordinary thinning has several commands.
Grades of Ordinary Thinning:
i) Light Thinning (A Grade): This is limited to the removal of dead, dying, diseased and suppressed trees.
ii) Moderate Thinning (B Grade): This consists in the further removal of defective eliminated stems and whips.
iii) Heavy Thinning (C Grade): This consists in the further removal of the remaining dominated stems and such of the defective co-dominants as can be removed without making lasting gaps in the canopy.
iv) Very Heavy Thinning (D Grade): The distinguishing features of this grade is that, it also takes some of the dominate, subject to the some condition of not making any lasting break in the canopy.
v) Extremely Heavy Thinning (E Grade): This is the heaviest thinning that can do in a crop without making permanent gaps in the canopy. More of the dominant stems even of class (a) are removed.
3) Crown Thinning:
The less promising one being removed in the interest of the best individuals; the dominated and suppressed stems are retained unless they are dead, drying or diseased. Aims at removing the inferior trees from among the dominant class.
Advantages of Crown Thinning:
Crown thinning offers several advantages over other methods of thinning:
i) Crown thinning provides better environment for growth and development of retained dominant trees.
ii) The trees of lower crown classes are not removed.
iii) The pressure of trees of lower crown classes results better pruning of side branches.
iv) It helps in protection of the site and reduces the damages due to frost, snow, wind etc.
Disadvantages of Crown Thinning:
The main disadvantages of crown thinning are
i) There is higher root competition for moisture and nutrients.
ii) Abstraction in felling, logging and extraction of tinned material.
iii) Crown thinning is more flexible method than ordinary thinning. It requires greater skill in execution.
iv) Closer look on suppressed and dominated trees would be necessary.