Thinning
Objectives
• Consider basic factors in the planning of
a thinning operation
• Know different methods of thinning
Reasons to Thin
• Maintain vigor of the stand
• Shift growth onto smaller number of
trees
• Salvage potential mortality
• Early financial returns
• Non-timber aspects
Decisions
1. When?
2. How much?
3. Which trees?
When?
• Crowdedness (growing
space)
– Live crown ratio
– Diameter growth (rings)
– Density management diagram
• Diameter distribution
• Growth model
• Rate of return
How much?
•
•
•
•
When is next action?
Thinning costs
Re-occupancy of growing space
Type of thinning
Which trees?
• All previous factors
• Logistics
• Reality
Methods of thinning
• Low
• Crown
• Selection
• Geometric
• Free
Low thinning
• Trees removed from lowest crown classes
• Mimics natural thinning
• Easy to select trees
• Has less effect on relative density
Pre-thinning
18
Number of Trees
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Diameter Class
7
8
9
Low thinning
18
16
14
12
10
Cut
Uncut
8
6
4
2
0
1
2
3
4
5
6
7
8
9
Low thinning example
• Percent of trees removed – 49%
• Percent basal area removed – 28%
• d/D - .74
d/D
[Average diameter of trees harvested]
[Average diameter of stand before
harvest]
Crown thinning
• Trees removed from upper crown classes
• Favor development of best trees
• Bulk of intermediate and healthier
portion of upper crown classes remain
• Better financial return than low thinning
• Greater effect on relative density
Pre-thinning
18
Number of Trees
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Diameter Class
7
8
9
Crown thinning
18
16
14
12
10
Cut
Uncut
8
6
4
2
0
1
2
3
4
5
6
7
8
9
Crown thinning example
• Percent of trees removed – 26%
• Percent basal area removed – 29%
• d/D – 1.07
Selection thinning
•
•
•
•
•
Thinning of the dominants
Can be high-grading
Can reduce potential growth
Greatest financial return
Greatest effect on relative density (but
may not increase growth rate)
Pre-thinning
18
Number of Trees
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Diameter Class
7
8
9
Selection thinning
18
16
14
12
10
Cut
Uncut
8
6
4
2
0
1
2
3
4
5
6
7
8
9
Selection thinning example
• Percent of trees removed – 26%
• Percent basal area removed – 47%
• d/D – 1.39
Geometric thinning
•
•
•
•
Usually row or strip thinning
Can lead to lopsided crowns
Less chance to remove damaged trees
Low harvesting costs
Pre-thinning
18
Number of Trees
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Diameter Class
7
8
9
Geometric thinning
18
16
14
12
10
Cut
Uncut
8
6
4
2
0
1
2
3
4
5
6
7
8
9
Geometric thinning example
• Percent of trees removed – 29%
• Percent basal area removed – 29%
• d/D – 1.00
Thinning examples
Low
Crown
Selection Geometric
Number
of trees
49%
26%
26%
29%
Basal
area
28%
29%
47%
29%
d/D
.74
1.07
1.39
1.00
Free thinning
• A mixture of all thinning types
• Often used in first entry in a very
irregular, single cohort stand.
• Example: Slow invasion so dominants are
older and very rough (low value);
codominants are very dense; logging
machinery access is difficult