2. • Stand density management is the process of
controlling the level of growing stock through
initial spacing or subsequent thinning to realize
specific management objectives.
4. WHAT is Thinning???
• Tending operation
• Felling of trees
• Carried out in an Immature stand
• For Improvement of growth and form of elite trees
• Without permanently breaking canopy
• Number of trees are reduced.
• Carried out in sapling stage till beginning of regeneration
period.
• In even aged and pure plantations, or nearly even aged
crop or even aged groups of tree in plantations
6. OBJECTIVE OF THINNING
• wood products from stands that are for long-term end-
uses;
• to lock up carbon from the atmosphere and store it as
woody biomass.
• material produced in thinning can be used as wood fuel, a
source of renewable energy, to help reduce fossil fuel
emissions.
7. OBJECTIVE OF THINNING
• Improve hygienic condition of forest stand
• To create best condition for growth of trees
• To salvage the anticipated losses of the merchantable volume-20% loss
happens
• To have desirable composition of crop
• Thinning material contribute 20 to 50 % to total stand yield
• To reduce rotation: early attaining of exploitable diameter
• Good mother tree
• Improved wood quality
• Uniform rate of growth
• Reduced form factor
• Intermediate yield
• Reduction of disease and pests
10. Before planning the nature and intensity of thinning the preference between the intensity of
thinning and quality of thinning should be decided.
The trees remaining after the thinning should be able to compensate for the loss in increment by
trees removed in thinning.
There will be an optimum stocking for a given site and species.
For this individual trees are classified by height and size of crown and thinning is decided on the
basis of which classes of trees are fit to be removed for maintaining the desired qualitative and
quantitative nature of the thinning.
The main purpose of the thinning is to release more space for future development of trees, the
freedom of crown is the guiding factor for thinning purpose.
The retention of trees per unit should be decided first and then the number of trees to be removed
should be marked accordingly.
The development of crown and stem are the deciding factor for sub-classification of the dominance
classes of trees for the given site and species.
TREE CLASSIFICATION BASIS
11. TREE CLASSIFICATION IN REGULAR
FORESTS
(I) Dominant trees (D or d1)
It includes the trees that form the uppermost leaf canopy. They are the tallest trees that determine the top level
of canopy they are also called pre-dominant trees.
(II) Co-dominant trees (CD or D2)
These are shorter than dominant.
About 5/6 of the height of dominant.
(III) Sub-dominant trees (SD or D3)
They do not form part of the uppermost leaf canopy.
Their height is about ¾ that of the tallest trees.
They are also called dominated trees.
(IV) Suppressed trees
The height of the suppressed trees are about ½ to 5/8 of the height of the best trees.
Suppressed trees grown below the crowns of the other trees in the stand.
The leading shoots are over-topped by their neighboring trees or at least shaded on all sides by them.
12. (V) Wolf trees (W)
The wolf trees are large, coarse and misshapen trees.
(VI) Whips (Wh)
This class comprises bent over and badly leaning trees.
Whips have tall, thin stems which are unstable and may cause damage to other trees when they sway.
(VII) Dead, dying and moribund trees (m)
This category consists of trees that are dead or at the point of death.
(VIII) Disease trees (k)
It includes trees that are infected with parasites and their growth is seriously affected due to infection.
(IX) Reproduction or Regeneration (r)It consists of recruits or regeneration.
TREE CLASSIFICATION IN REGULAR
FORESTS
13. (X) Overmature or veterans
i. It consists of over-matured trees.
ii. In spite of these classifications the basis three types of stem
and crown classification.
iii. The good, medium, bad and whips are shown by using
symbols a, b, c, d respectively i.e.
Good = a
Medium = b
Bad = c
Whips = d
iv. Therefore the further classification of D2 will be D2 (a), D2 (b), D2
(c), or D2 (d) or that of s will be S (a), S (b), S (c) and soon.
No thinning should be carried out on the edge or periphery of the
plantation.
The crown spread may be taken as a better indication than canopy position to
understand growth potentialities of a tree.
TREE CLASSIFICATION IN REGULAR FORESTS
14.
15.
16.
17.
18. CLASSIFICATION ON THE BASIS OF CROWN
The crown spread may be taken as better indication than canopy position to understand growth potentialities of
a tree.
For this tree may be classification on the basis of the crown with average stem spacing as shown below:-
i. Spaced
Trees with free crown spreading having less than or equal to ¾ that of spacing.
ii. Co-space
Trees with a free crown spread having ¾ to ½ (50-75%) that of the spacing.
iii. Sub-space
Trees with the spread of free crown less than half but more than one-fourth ¼ of the spaced.
iv. Mal-spaced
Trees with a very small spread of trees crown which is less than a quarter of the spaced.
v. De-spaced.
Trees will no free crown with little vigour.
vi. Dead, dying and low yielding trees
19. STATISTICAL BASIS
• In regular plantations the density and site quality vary considerably and it is
not possible to define crown and canopy classes.
• For this the number of trees to be retained per unit area and their spacing
should be numerically fixed.
• After fixing the number of trees per unit area the remaining trees can be
marked and removed.
• Fix initial and final spacing
21. Mechanical thinning
• Some thumb rule used
• Removal or alternate rows,
• Removal of alternate diagonals or
• Removal of every second third, fourth line etc.
• Where the spacing is irregular the minimum spacing is irregular the minimum
spacing is maintained by using “standard stick” method.
• Row Thinning
• Spacing Thinning
Advantage:
Simple to apply
Disadvantage:
Vigorous trees removed
22. Low or ordinary thinning
• GERMAN THINNING” or “THINNING
FROM THE BLOW
• Removal of inferior individuals starting from
the suppressed class to dominated class and
ultimately some of the dominant class.
• In regular crops.
• those trees which have been unsuccessful in
the struggle for growth are removed first.
Advantage:
•Demand for small timber
•Suited for light demander species . Chir pine, sissoo
• Simple to apply
•Improves the HYGENIC condition
• Should not be carried out where there is a danger of soil erosion.
• High volume production
• Lower crown classes helps in the natural regeneration of the species.
Disadvantage:
exposure to the soil, Increases the fire hazards, expensive due to thorny
24. GRADE OF ORDINARY THINNING
A-Grade Light thinning
removal of dead, dying, diseased and suppressed trees i.e. Class V, IV, and III.
B-Grade Moderate thinning.
In addition to trees in A-grade further removal of defective dominated stems and whips. i.e.
Class, V, IV, III, II (b), I (d) and an occasional I (c).
C. Grade (Heavy thinning)
This includes trees in grade A and B and all remaining dominated, defective, co-dominants
that may be removed without making lasting gaps in canopy i.e. Class V, IV, III, II and I
(b), I (c) and I (d).
D-Grade (Very Heavy Thinning)
This includes trees of all above grades and some good dominants so that no lasting or
permanent gap develop in canopy.
The removal of trees are made from the Class V, IV, III, II, I(b), I (c), I (d) and some I (a).
Low or ordinary thinning-Grades
25. E-Grade (Extremely Heavy Thinning)
This type of thinning is adopted mainly for research purposes.
This is the heaviest thinning that can be made in the crop without creating permanent
gaps in the canopy.
Many dominant stems including that of Class I (a) are also removed.
It is always better to make C-grade or D-grade thinning in a dense crop in which
thinning has been unduly delayed.
The removal of trees should be Economic or Hygienic value.
Low or ordinary thinning-Grades
26. Crown thinning/french or high thinning
“Thinning from above”.
selective thinning in which thinning is primarily directed to the dominant trees in a regular
crop, the less promising ones being removed in the interest of the best available individuals:
The dominated and suppressed stems are retained unless they are dead, dying or diseased.
The crown thinning favours the crown development of the selected potential final crop
Retaining trees of lower crown classes can help in the natural pruning of the dominant trees
which are to make the final crop.
27. The attention in concentrated still further on the selection of ELITES or ALPHA
stems, evenly spaced over the ground, which are retained upto maturity or till the
last thinning or two, and thinning operations may accordingly be directed primarily
to the removal of other stem hindering their optimum development.
The number of future stems to be required at the rotation are first selected and
retained evenly distributed over the area.
After selecting and marking the elite tree, if considered necessary, they are cut
otherwise left for the protection of the site.
28. Free thinning
• This is also called HECK’S free thinning and is a modification of crown thinning.
• It is also called “ELITE THINNING” or “SINGLE STEM SILVICULTURE”.
• The emphasis on freeing the selection of most promising stems called “ELITE or
ALPHA STEMS” from the competition of their less promising neighbours.
• The crop after free thinning do not differ much in appearance from those subject
to crown thinning, but the attention is concentrated on the trees to be retained
rather than on the trees to be removed, just as in seeding felling.
29. Crown thinning
Advantages
• provides better environment for growth and development of
retained dominant trees.
• The trees of lower crown classes are not removed.
• The pressure of trees of lower crown classes results better
pruning of side branches.
• It helps in protection of the site and reduces the damages due
to frost, snow, wind etc.
Disadvantage
• higher root competition for moisture and nutrients.
• Problem in felling, logging and extraction of thinned material.
• It requires greater skill in execution.
30.
31. Light Crown Thinning
removal of dead, dying, diseased and wolf trees with such of the defective and after them the
better dominants as are necessary to leave room for further development of the best available
trees evenly distributed over the area.
The trees belong to classes V, VI, I (d), I (c), many of I (b) and a few of I (a) but not III and II
are removed.
Heavy Crown Thinning
favouring the selected best trees by removing all the remaining I (b), which can be taken without
creating permanent gaps and more of I (a) i.e. classes V, IV, I (d), I (c) most or I (b), some of I
(a); but not III and II.
The final crop is target to achieve certain stocking e.g. 500 to 600 trees per hectare.
The dominated and suppressed trees are removed.
Crown thinning-grades
32. Advance thinning
• Craib’s thinning tried by him in wattle and Pine
• Before setting of competition trees are removed to allow
growth of remaining trees.
• Not practically applicable espcially in light demanders
• Applied in India in Chir, Teak, Sal
33. Numerical thinning
• yield table are needed as standard of reference.
• number of stems per unit area, diameter height serve as a
guiding for the optimum density of the crop.
• These factors vary with the site quality.
In the absence of yield table following approaches are used:
• No of stem and diameter relations
34. First thinning and other considerations
• Should take place before adjoining trees check one another’s growth.
• Should not be postponed on the ground that the poles obtained will be
non-saleable or uneconomic.
• Should be taken on the basis of height or size attained.
• The heavy thinning should not be carried on poorer sites, drier areas and
steeper slopes, because the gaps may not filled up due to poor growth of
trees.
• All thinning should be done on the silvicultural lines.
• The light demander species may require heavier thinning as compared to
the shade bearer species.
• If the mechanical thinning is not possible due to low survival rate, poor
growth, and interference by other species, it is best to carry out
silvicultural thinning.
• Some admixture of secondary species may be retained where this is
desired on silvicultural or protection grounds.
35. Thinning in irregular crops
Difficult to classify tree in an irregular crop.
• The thinning is an irregular crop is done by selection method.
• The trees to be cut is that which restrict the growth of their neighbours on all sides
and should into more valuable than their neighbours.
• The aim should be to maintain a crop of all diameter classes in a sufficient
number of maximum sustained yield.
• The valuable species are retained whereas inferior trees of all diameter classes
are removed.
• The removal of trees is carried out in diameter classes.
• It aims at continuous improvement by repeated removal of inferior stems in all
diameter classes so that basal area or standing volume becomes more or less equal
to theoretical ideal value.
CROWN
FREEDOM
FREE RESTRICTED CONFINE
Crown
development or
crown size
Well developed or
large
Average or
medium
Poor or small
36. Factor affecting thinning practice
Site Factors
Relatively close canopy on the poorer sites should be maintained.
On low quality sites heavy openings should not be made.
The spacing out widely in earlier stages should not be carried out on hot, dry,
slopes, on poor soils and on all sites where grass and other weed invasion is likely
to occur.
A poor site will usually support less stems per hectare than a good one.
For chir pine having crop diameter of 30 cm the number of stems are 420 (Q. C.
II) per hectare and 306 (Q. c. III) and Deodar the number is normally independent
of site quality.
37. Factor affecting thinning practice
Nature of Species
The shade-bearers are more tolerant of crown than the light demanders
therefore more frequent thinnings is needed for light demanders species.
Light demanders usually show good response to ordinary thinning where
as shade-bearers to crown thinning.
Chir pine and sissoo, being light demanders require heavier grades of
ordinary thinning.
For Deodar advance thinning is suitable as the site is not likely to degrade
even after expose.
38. Factor affecting thinning practice
Age
The crown formation depends on age and in young ages when the crown
formation is not completed mechanical thinning or stick thinning may be
done with succession.
The light demander species require heavier grade of thinning at frequent
intervals in younger crops.
some species in middle age or maturity require crown thinning.
39. Disadvantage of thinning:
• Increased taper
• Increase branch knots
• Thinning is coupled with high pruning
• Less dense wood and poor quality
