QUẢN LÝ THẢM THỰC VẬT RỪNG: THINNING METHODS CÁC PHƯƠNG PHÁP TỈA TƯA

Mechanical or Geometric: the thinning of trees in either even or uneven age stand involving removal of trees in rows, strips, or by using fixed spacing intervals Frequently, these are the first thinnings in young stands that are densely crowded andor relatively uniform with little differentiation into crown classes. Spacing criteria are only considerations No impact on DBH distributions

Mechanical thinning

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Mechanical or Geometric: the thinning of trees in either even- or uneven age stand involving removal of trees in rows, strips, or by using fixed spacing intervals

Frequently, these are the first thinnings in young stands that are densely crowded and/or

relatively uniform with little differentiation into crown classes

Spacing criteria are only considerations

No impact on DBH distributions

Mechanical thinning (row thinning)

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Cut all trees in rows or strips at fixed intervals throughout the stand They are often utilized for the first thinning(s)

in plantations where the rows are readily apparent The removal of every third row is the most common practice

A mechanical row thinning in a pine plantation stand (Adapted from Fact Sheet G3398, Wisconsin Woodlands: Intermediate Cuttings in Forest Management, University of Wisconsin-Extension)

Row thinning

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Mechanical thinning (spacing thinning)

Spacing thinning

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Low thinning

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Thin from below, ordinary thinning, German thinning

Low thinning or thinning from below is the removal of trees from the lower crown classes (the smallest

trees) to favor those in the upper crown classes (the largest trees)

In general there are 4 Grade of low thinning: Grade A; B; C; D

Grade is degree of thinning

Grade of low thinning

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Low thinning

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Crown thinning

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This crop tree, released on two to three sides by cutting competing trees, is now free to grow.

Crown thinning, thinning from above, high thinning, thinning in the dominant, French thinning:

• Remove of trees from the dominant and co-dominant crown classes in order to favor the best trees of those same crown classes.

• Remove large trees to favor other large trees (remove fairly large trees, but not small trees!)

• Remove more volume per unit basal area than that of low thinning

• Reduces future competition on other large trees, increases diameter growth rate

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Crown thinning

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timber and veneer logs

of quantity

Crown thinning

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Thinning of dominants, diameter-limited thinning, Borggreve method

• Remove large trees to favor small trees

• Maximized current economic return

• Higher income earlier in stand

• Relies on smaller trees to respond to open growing conditions

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Selection thinning

Selection thinning

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Selection thinning

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Selection thinning

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Free thinning

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The removal of trees to control stand spacing and favor desired trees, using a combination of thinning criteria without regard to crown position

 When faced with a stand with a irregular structure, it may not make sense to do any of the above thinnings

 Apply all other elements of thinning at once

 Thin to improve stand structure

 Application/rotation sets stage for other thinnings

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Crop tree management

 Crown-touching release

 Trees which fit/will fit your needs

 Northern and eastern hardwoods

 Where no suitable crop trees are found, do not cut any trees

 Space crop trees out; no more than two together

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How to choose?

 Stand conditions/composition

 More flexibility early in rotation

 Generally harvest downward through canopy over time

 Start heavy, then get lighter

 Thinning should be applied in some times e.g Selection/liberation, then crown/free,

then low

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Management Concerns

 Immediate return

 the larger the trees that are thinned, the bigger the immediate return

  Future development of stand

 growth of large vs small trees

 improvement of value

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Management Concerns

 Time - earlier in rotation, trees tend to be smaller

 Development - promote the growth of small trees vs big trees in current stand

 Markets - what are the critical sizes to profitably log?

 Economics - try to put off investments, schedule revenues sooner

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Management Concerns

Conveys conception of how you want stand structure altered

Trees to take Vs trees to leave

 Tree size (dbh, height)

 Stem quality (knots, sweep, defects)

 Crown (vigor)

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