METHODS OF THINNING 

• LOW – Thinning from below (German)
• CROWN - Thinning from above (French)
• SELECTION – Thinning of dominants
• GEOMETRIC – Thinning by rows or mechanical means

*Low, Crown, and Selection methods are based on crown position & development . Geometric method is based on spatial distribution. 

    I.  Low Thinning: 

• Trees are removed from lower crown classes

• As thinning becomes more intensive, higher crown classes are removed

•  Simulates and accelerates natural processes 

4 Grades:

(A) 

Ø     Very light; removes only overtopped, dead or nearly dead trees

Ø     Basically a salvage operation

Ø     Canopy is left unchanged 

(B)

Ø     Light

Ø     Also removes the intermediate crown classes

Ø     Also has little risk of reducing GROSS production of wood, since removals are not “producers” 

(C)

Ø     Moderate

Ø     Some codominants are also cut

Ø     This level of cutting begins to have impact on original crown canopy 

(D)

Ø     Heavy

Ø     Many, but not all codominants are cut 

(E)

Ø     Continuing to this level of cutting where all but the dominants are removed is generally considered too severe for thinning.  This may be considered to appear similar to a shelterwood regeneration-type cut. 

LOW THINNING - ADVANTAGES 

1)     Simple, minimum skill needed, difficult to err

2)     Simulates natural processes by removing stressed, suppressed, declining trees

3)     Useful where lower crown classes are merchantable, but will not respond if released (intolerant).

4)     Frees up nutrients for use by residual stems 

LOW THINNING - DISADVANTAGES 

1)     Creates vacancies in lower stratum of stand

2)     Not preferred where troublesome or undesirable understory may develop

3)     Favors the establishment of Ribes in understory of white pine stands

4)     Generally, thinned material is not merchantable 

    II.   Crown Thinning 

• Removes trees from middle and upper crown classes
• Stimulates development of trees in same crown class
• Objective: to open canopy to favor development of most promising trees
• REMOVALS are: mostly co-dominants (some dominants & intermediates)
• REMOVALS are: trees interfering with CROP trees
• REMOVALS are: strong competitors
• DIFFERENT FROM LOW THINNING: focuses on different crown classes
• DIFFERENT FROM LOW THINNING: MOST intermediate & overtopped trees will remain, if healthy
• BASIC DECISION CRITERIA: POTENTIAL
• Can be applied uniformly throughout the stand, releasing many promising trees, or Concentrated on just a few Crop trees per acre

CROWN THINNING – ADVANTAGES 

1)     Higher value of return from harvesting larger trees

2)     Decelerated the dying of lower branches

3)     Stimulates overall stand growth without losing overall productivity

4)     Removes comparable volume/acre as LOW thinning, but from far fewer and larger trees

5)     More flexible when selecting residual/removed trees

6)     Regulated by basal area measure and stand density 

CROWN THINNING – DISADVANTAGES 

1)     Root competition from lower crown classes may still influence crop trees

2)     Requires more skill

3)     Makes no provision for subordinate leave trees – creating 2 stand categories

III. Selection Thinning

• Dominant trees removed to stimulate growth of trees in lower crown classes

• Trees are selected based on size, quality, crown position

• Trees in lower crown classes are left uncut to become the dominant crown position for future management

SELECTION THINNING - ADVANTAGES

1) High immediate monetary return is achieved

2) Can be flexible when applied on some sites

3) Can be applied to conifers & mixed stands

SELECTION THINNING - DISADVANTAGES

1) Increased susceptibility to physical & biotic damage

2) May reduce genetic quality on site

3) Must be properly adapted to each individual stand

4) May become "high-grading" if not careful when selecting removals & residuals

5) Difficult to apply correctly, easy to err

6) Lower crown class trees (especially intolerants & mid-tolerants) will not respond well to release

IV. Geometric Thinning

• Trees to be removed are chosen with regard to position on the ground rather than position in the canopy

• Can be used in pre-commercial operations (often mechanical) or commercial

• Can be based on spacing of fixed intervals of distance

• Can be applied to rows, lines or strips in artificially planted stands

GEOMETRIC THINNING - ADVANTAGES

1) Simple to apply

2) Permits easy future management

3) Produces variety of products if performed in merchantable stand

4) Retains some trees in all crown classes

GEOMETRIC THINNING - DISADVANTAGES

1) Does not maximize potential benefit (profit nor growth) from thinning activity

2) Removes "promising" trees as well as poor trees

3) May be visually unattractive

4) Releases trees on only 1 or 2 sides