 | Forestry training manual Inter-America Region |
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Session XXIII The principals of pruning and thinning
Learning How to Make and Use a Diameter Tape
Total Time: 4 hours
Goals:
- To have trainees learn the principals of pruning and thinning.
- To have trainees understand the concept of a diameter tape and its use.
Overview
In this session, participants will come to understand the principals of both pruning and thinning of trees. They will have actual "hands on" practice in pruning trees and thinning a woodlot. Participants will make a diameter tape and learn how to use it. They will measure trees with diameter tapes before thinning.
Exercise
1. Pruning and thinning theory and practice.
2. Make a diameter tape and learn how to use it.
Materials
Flip chart, marker pens, tape, pruning saws, ban saw, standard dressmaker measuring tape (metric), indelible pens.
Exercise I Learning How to Make and Use a Diameter Tape
Total Time: 1 hour
Overview
A diameter tape is a simple tool for measuring the diameter of a tree at breast height (DBH). The trainees will first learn how to make a diameter tape. After having made diameter tape, trainees will learn how to measure tree at DBH.
Procedure
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Time |
Activities |
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1. Participant who has taken this on as a special project teaches other trainees how to make diameter tape. It is inexpensive and trainees can teach others how to make and use this tool. The directions should be similar to those listed below. Measurements are also included. |
Description
A diameter tape, although it measures the circumference of a tree, is calibrated to read out the diameter measurements. The tree is measured at breast height (DBH);
i.e., measure tree diameter at 4 1/2 feet above ground level.
Fig. 12
Thus a tree that measures 135.09 cm in circumference has a diameter of 43 cm.
Method:
Using attached scale mark off dress maker tape every 3.14 cm with indelible marking pen. Allow to dry
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Diameter Tape |
C=<p > D |
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1 |
= |
3.14 cm |
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2 |
= |
6.28 |
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3 |
= |
9.43 |
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4 |
= |
12.57 |
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5 |
= |
15.71 |
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6 |
= |
18.85 |
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7 |
= |
21.99 |
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8 |
= |
25.13 |
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9 |
= |
28.28 |
|
10 |
= |
31.42 |
|
11 |
= |
34.56 |
|
12 |
= |
37.70 |
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13 |
= |
40.84 |
|
14 |
= |
43.98 |
|
15 |
= |
47.13 |
|
16 |
= |
50.27 |
|
17 |
= |
53.41 |
|
18 |
= |
56.55 |
|
19 |
= |
59.69 |
|
20 |
= |
62.83 |
|
21 |
= |
65.98 |
|
22 |
= |
69.12 |
|
23 |
= |
72.26 |
|
24 |
= |
75.40 |
|
25 |
= |
78.54 |
|
26 |
= |
81.68 |
|
27 |
= |
84.83 |
|
28 |
= |
87.97 |
|
29 |
= |
91.11 |
|
30 |
= |
94.25 |
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31 |
= |
97.39 |
|
32 |
= |
100.53 |
|
33 |
= |
103.68 |
|
34 |
= |
106.82 |
|
35 |
= |
109.96 |
|
36 |
= |
113.10 |
|
37 |
= |
116.24 |
|
38 |
= |
119.38 |
|
39 |
= |
122.53 |
|
40 |
= |
125.67 |
|
41 |
= |
128.81 |
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42 |
= |
131.95 |
|
43 |
= |
135.09 |
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44 |
= |
138.23 |
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45 |
= |
141.28 |
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46 |
= |
144.52 |
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47 |
= |
147.66 |
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48 |
= |
150.80 |
DAP Diametro altura de pecho (diameter at breast height [DBH])
Exercise II The Principals of Pruning and Thinning
Total Time: 3 hours
Overview
In this exercise trainees learn the principals of pruning and thinning. Trainees also practice actual pruning and thinning.
Procedure
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Time |
Activities |
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1. Technical trainee gives lecture on |
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45 minutes |
pruning and thinning with the use of saws and axes. If a trainee has extensive experience in pruning and/or thinning, he is asked by technical trainer to demonstrate proper techniques to other trainees. If no trainee has this specific experience, technical trainer does demonstration. |
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2. Technical trainer now takes trainees to |
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1 hour |
nearby stand of trees in need of pruning and trainees prune trees. |
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3. Trainees also thin a few trees from a |
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1 hour |
stand that needs thinning. |
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4. Technical trainer supervises trainees |
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15 minutes |
and summarizes at end of exercise. |
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Explanation of these activities is outlined on the following pages: |
Materials: Bow saws, axes, diameter tapes (made in previous exercise).
PRUNING (Poda)
Objectives of Pruning:
1. to produce knot free wood,
2. to allow easy access to the forest,
3. to decrease fire hazards,
4. to increase value of stand,
5. to improve the aesthetics of the forest.
Products - Firewood
Advantages:
1. make clear wood production,
2. less taper in tree,
Disadvantages:
1. growth rate decrease.
Methods
1. It is best to use a pruning saw attached to a pole if higher limbs are to be cut.
2. Use an ax or a machete (on lower limbs) only if worker is really proficient in the use of these tools. Limbs must be cut flush with stem of tree which requires great skill with a machete or an ax.
Pruning - percent of crown to be removed
Pruning - cut should be flushed to the hole of the tree.
Undercut - to avoid stripping bark off tree trunk.
POSSIBLE PRUNING SCHEDULE
Schedule depends on:
1. species
2. growth rate (site)
Example
1st pruning age 6 - 7 years
2nd pruning age 8 - 9 years
3rd pruning age 10 - 12 years
Economic considerations:
1. For what products are the trees being grown?
2. Are prices for pruned trees (or logs or lumber from pruned trees) higher than for unpruned trees?
THINNING
Objectives:
To provide growing space to selected trees (crop trees) so that these trees have the highest annual growth increment possible.
Products:
1. firewood
2. pulpwood (or wood for chips)
3. posts
4. poles
5. rafters
6. small saw logs
Methods - mechanical (systematic)
1. row removal
2. removing every other tree
Fig 15
- Either system removes 1/2 the trees.
- Both systems can easily be used on young trees.
- Easy to implement and supervise.
Marking for Thinning
Depending on local custom either "leave" or "take" trees are marked. Trees are usually marked at eye level and on stump (all marks facing the same direction).
a. Ax markings are easy, but they can easily be changed.
b. Paint is better but more expensive.
- There should be very close supervision of cutting and removal work.
- Loggers tend to want to remove as much volume as possible.
D + X Method
The average diameter in inches + some factor (X=1 to 8) is equal to the average spacing as expressed in feet.
Example:
Average DBH=12"
factor = 6
12+6 = 18
Average spacing should be 18 feet between trees.
A good marking method should consider:
1. crown growing space,
2. position of tree in stand structure,
3. defects: rot, top breakage, forks, crook, etc.,
4. root space,
5. openings in stand.
It is best to leave dominants and codominants with room to expand their crowns; remove intermediates, supressed and defective trees. If a systematic thinning was planned with two thinnings per rotation, the results might be the following: (consider a plantation originally planted 2 meters by 2 meters, 2500 trees/hectare).
- Removing every other row would leave 1250 trees/hectare spacing 2 meters by 4 meters.
- Removing 1/2 the remaining trees would leave 625 trees/hectare with spacing of 4m X 4m.
- It is generally thought that there will be between 600 - 700 crop trees per hectare at the final harvest, however this depends greatly on the species used.
Economics of Thinning
Costs:
marking
falling & bucking
yarding & loading
transport
administration
Total Costs
Price of Materials
price of material
Total Cost
Profit
- The largest cost will probably be transport. The closer to market, the better.
- Keep yarding costs down by keeping maximum yarding distance as small as possible (+/-200 meters to loading site).
- If labor is cheap, hand falling and bucking might be less costly, although slower.
- If machinery is expensive, using animals for yarding will probably be less costly, although slower.
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