Chapter 8 (Part 2): Tending Operations
Chapter 8 (Part 2): Tending Operations
Thinning Methods, Improvement Felling, Girdling, Pruning and Climber Control
1. Key Concepts
Ordinary Thinning
Also called German Thinning. Trees are primarily removed from lower canopy classes, progressing upward into the upper canopy in heavier grades.
Crown Thinning
Also called French Thinning. Selected upper-canopy competitors are removed to favor promising crop trees, while lower canopy trees are retained.
Free Thinning
Also called Heck's Thinning. Competing trees are removed around selected elite or crop trees, regardless of their canopy class.
Maximum Thinning
Stand density is reduced to the minimum required for maximum individual stem diameter growth without creating permanently unproductive canopy gaps.
Advance Thinning
Also called Craib's Thinning. Heavy fellings are carried out before crown competition begins.
Selection Thinning
Trees are removed from different age and diameter classes to maintain a balanced selection structure.
Improvement Felling
Removal of inferior, over-mature, diseased, malformed or suppressed stems from unmanaged or degraded stands.
Pruning
Removal of live or dead branches from standing tree boles, naturally or artificially, to produce knot-free, high-value timber.
Girdling
Removal of a continuous ring of bark, cambium and outer sapwood to disrupt downward phloem translocation and gradually kill undesirable trees.
Climber Control
Systematic cutting or uprooting of woody lianas and twiners that deform, groove or smother tree boles and crowns.
2. Ordinary Thinning Grades (Low Thinning)
Ordinary thinning removes trees mainly from the lower canopy. The intensity of removal increases from A-grade to E-grade.
| Grade | Name | Trees removed |
|---|---|---|
| A | Very Light | Dead, dying, moribund (Class 4) and suppressed (Class 3) trees. |
| B | Light | Class 4, Class 3 and defective dominated (Class 2) trees. |
| C | Medium / Standard | Class 4, Class 3, Class 2 and malformed or defective dominant (Class 1) stems. |
| D | Heavy | Class 4, 3, 2 and inferior dominants; well-formed dominants are retained with space between crowns. |
| E | Very Heavy | Additional healthy dominants are removed to provide maximum crown freedom to selected final crop trees. |
- A: Very Light
- B: Light
- C: Medium (Standard)
- D: Heavy
- E: Very Heavy
3. Crown Thinning Grades (High Thinning)
Crown thinning concentrates on releasing selected crop trees by removing competing trees in the upper canopy.
| Grade | Removal intensity | Purpose |
|---|---|---|
| L-Grade | Light crown thinning | Removes dead or dying trees and selected competing dominants or codominants interfering with crop trees. |
| H-Grade | Heavy crown thinning | Removes a larger number of upper-canopy competitors to provide complete crown freedom to selected crop trees. |
4. Comparison of Major Thinning Systems
| Thinning system | Primary target | Lower canopy treatment | Application |
|---|---|---|---|
| Ordinary | Lower canopy, progressing upward | Removed in standard C/D grades | Uniform even-aged plantations: Teak, Sal and Pines |
| Crown | Upper canopy: dominant and codominant competitors | Retained for soil shade and natural pruning of lower boles | Even-aged shade-bearing or mixed broad-leaved stands |
| Free | Competitors around selected crop trees | Retained unless directly competing with crop trees | Irregular plantations and high-value timber crops |
| Advance | Overcrowded plantation stems before competition | Removed before crown closure occurs | Fast-growing coniferous and wattle plantations |
| Selection | Different diameter and age classes | Selective removal to maintain stand structure | Uneven-aged or selection forests |
5. Mechanical and Numerical Thinning
Mechanical Thinning
Used in young, uniform plantations. Tree removal follows a predetermined spatial pattern rather than individual tree quality.
- Line thinning
- Diagonal thinning
- Row thinning
- Removal of every second or third row
Numerical Thinning
Thinning is guided by quantitative stand parameters, including:
- Basal area per hectare
- Crop density
- Number of stems per unit area
- Yield-table parameters
6. Ordinary vs. Crown Thinning: Canopy Removal
Ordinary Thinning
Bottom-up approach
Crown Thinning
Top-canopy release approach
7. Pruning: Principles and Operations
Pruning involves the removal of live or dead branches from the standing tree bole. It may occur naturally through canopy shading or artificially through tools such as saws and shears.
Why is pruning performed?
- To improve timber quality.
- To produce knot-free timber.
- To remove dead or unwanted branches.
- To improve the bole and timber value.
Artificial pruning height
Pruning is generally done up to ⅓ to ½ of total tree height. Pruning beyond one-half of total height should be avoided to prevent reduction in diameter increment.
Correct branch-cut execution
- Make the cut close to the stem collar.
- Avoid tearing the bark.
- Do not leave protruding branch stubs.
- Allow rapid callus formation and occlusion of the wound.
8. Girdling (Ringing)
Girdling is the removal of a continuous ring of bark, cambium and outer sapwood around the trunk. It interrupts the downward movement of sugars through the phloem.
Mechanism of tree death
9. Climber Control
Woody climbers and lianas may deform, groove or smother forest tree boles and crowns. Their control involves systematic cutting or uprooting.
Two-cut method
Important climber
Bauhinia vahlii – a massive woody climber requiring two-cut severing for control.
10. Important Scientific Names
| Species / Organism | Scientific name | Tending context |
|---|---|---|
| Heavy liana / climber | Bauhinia vahlii | Two-cut climber control |
| Teak | Tectona grandis | Early C-grade ordinary or mechanical row thinning |
| Chir Pine | Pinus roxburghii | Numerical thinning using basal-area checks |
| Sandalwood | Santalum album | Cleaning around host species |
11. Formulae and Quantitative Metrics
A. Pruning intensity
Where H = total tree height.
B. Thinning intensity using basal area
Example: If the initial stand basal area is 30 m²/ha and 6 m²/ha is removed:
The example illustrates the formula.
12. Important One-Liner Facts
- Ordinary thinning = Low thinning = German thinning.
- Crown thinning = High thinning = French thinning.
- Free thinning is also known as Heck's thinning.
- Advance thinning is also called Craib's thinning.
- Craib developed advance thinning for South African pine and wattle plantations.
- C-grade is the standard operational grade of ordinary thinning.
- Artificial pruning should not exceed one-half of total tree height.
- Two-cut climber control involves cuts at ground level and approximately 1.5 m height.
- Girdling interrupts phloem translocation and starves roots.
- Numerical thinning uses basal area, crop density and stem number parameters.
13. Mnemonics and Memory Tricks
1. Ordinary thinning grades: A-B-C-D-E
- A – Very Light
- B – Light
- C – Medium
- D – Heavy
- E – Very Heavy
2. Ordinary thinning synonyms: O-L-G
Ordinary = Low = German
3. Crown thinning synonyms: C-H-F
Crown = High = French
4. Key method associations
- Heck → Free thinning
- Craib → Advance thinning
- German → Ordinary / Low thinning
- French → Crown / High thinning
14. Quick Revision Box
- Ordinary thinning: Bottom-up removal; German method.
- Crown thinning: Selective removal of upper-canopy competitors; French method.
- Free thinning: Crop-tree-centred; Heck's method.
- Advance thinning: Heavy early thinning before crown competition; Craib's method.
- Selection thinning: Removal across age and diameter classes in uneven-aged stands.
- C-grade: Medium and standard ordinary thinning grade.
- Pruning: Maximum height ≤ ½ H.
- Girdling: Phloem interruption causes root starvation.
- Climber control: Two cuts, at ground level and 1.5 m.
- Numerical thinning: Uses basal area, crop density and stem number.
15. Interactive MCQ Quiz
15 questions. Tap an option to see the correct answer and explanation straight away, then go to the next question.
Chapter 8 (Part 2) | Tending Operations
Comments
Post a Comment