Thinning as a tool of close to nature forestry

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Thinning as a tool of close to nature forestry

• Igor Štefancík
• Forest Research Institute, Zvolen
• Slovakia

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• Close to nature forestry, can be defined as a
  planned utilisation of natural processes
  progressing in forest ecosystems and its
  regulation so as the developmental changes are
  desirable from the management point of view
  (Otto, 1995).
• The primary goal of forestry based on natural
  principles framed in this way is maintaining of
  such a structure of forest, which allows, along
  with a high yield, to fulfil other required
  functions as best as possible.

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Basic items of ecologically oriented silviculture

• formation of optimal structure of forest stands
  (tree species, age and spatial) corresponding to
  site condition and the management goals
• reduction of large-area system of management of
  forests and conversion to individual system, i.e.
  each individual tree it leads to limited
  application of schematic tending intervention and
  clear-cuttings.
• utilization of natural regeneration of forest in
  a maximum scale, if possible under the present
  conditions.

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From the above-mentioned follows

• stand structure and/or its regulation and changes
  are one of the key aspect within the framework of
  close to nature forestry
• formation of desired structure are carried out
  besides self-regulation processes also by
  silvicultural measures, especially by tending
• very significant appears the treatments in
  younger growth phases (young-growth stand,
  pole-stage stand)

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• not each thinning methods are suitable from view
  of the principles of close to nature forestry
• as an improper can be considered the thinnings
  from below, which cause the high levelling of
  stand canopy
• as a suitable appears combined thinning and crown
  thinnings (Schädelins qualitative thinning,
  French thinning, Danish thinning, and so on),
  which take into account also the suppressed layer
  of the stand canopy

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Conception of free crown thinning

• developed in Slovakia by Prof.Dr.L.Štefancík for
  tending of beech (broadleaved) stands.
• this method can also be applied in mixed
  (spruce-fir-beech) stands.

• 1929 - 2002

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• The main goal of this method is cultivation of
  the trees of selective quality, i.e. promising
  and target (crop) trees.
• This method combines five methods of selection,
  when the principal one is considered positive
  selection at crown level of the canopy, followed
  by other four ones positive at suppressed level
  of canopy, negative, sanitary and maturity
  interventions which are focused on cultivation of
  stand filler (Table 1).

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Silvicultural analysis of the free crown thinning
Method of selection, intervention Objective of intervention in the stand component (growth class) Purpose of intervention Purpose of intervention
Positive at the crown level dominant and co-dominant (1 to 2) suppressed level (3) suppressed level (4 to 5) cultivation of the trees of selective quality - release of lateral space of their crown - release of space of the lower part of their crown - removal of individuals which lash their stem
Positive at the suppressed level suppressed level (3 to 5) removal of undesirable individuals from the point of view - their spacing i.e. thinning of suppressed level to ensure the tending and protective function of this component
Negative dominant, co-dominant and suppressed level (1 to 5) removal of undesirable individuals from the point of view - quality of stem and crown improvement of the average mass quality of the stand as a whole and ensuring replacement for cancelled the trees of selective quality
Sanitary dominant, co-dominant and suppressed level (1 to 5) removal of undesirable individuals from the point of view - sanitary condition to increase stand resistance
Relative maturity dominant, co-dominant and suppressed level (1 to 5) removal of undesirable individuals from the point of view - tree species to increase production of economically desirable tree species
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We distinguish following categories of trees

• Qualitative trees individuals with suitable
  qualitative signs of stem and crown
• Promising trees (PT) qualitative trees with
  desired criterion
• Target (crop) trees (CT) promising trees, for
  which it is supposed to achieve rotation age
• Trees of selective quality PT CT

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Criterion for the selection of the trees of
selective quality

• Qualitative - satisfactory quality characters of
  stem and crown
• Dimensional suitable dimensional requirements
  as for height and diameter
• Spacing appropriate spacing in the stand,
  regulated during development course by the method
  of the promising trees and/or by the method of
  crop trees.

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Characteristics of target (crop) trees in a pure
beech stand as variants of the production goal.
Age 110 to 130 years Beech 100 Absolute site
class height 26 to 38 (by Halaj)
Variant Site Crop trees Crop trees Crop trees Crop trees Crop trees Crop trees Crop trees
Variant Site number N pcs. ha-1 average average Volume of wood with d1.3 gt 7cm under bark Volume of wood with d1.3 gt 7cm under bark Volume of wood with d1.3 gt 7cm under bark Volume of wood with d1.3 gt 7cm under bark
Variant Site number N pcs. ha-1 spacing S (m) diameter d1,3 (cm) total total venner logs venner logs
Variant Site number N pcs. ha-1 spacing S (m) diameter d1,3 (cm) m3.ha-1 m3.ha-1
1 2 acid 203 198-217 186 173-200 7.3 7.6 38 40 366 376 73 75 220 225 44 45
3 4 5 fertile 168 156-180 152 142-165 130 121-140 8.0 8.4 9.1 43 45 50 397 401 425 79 80 85 238 241 255 48 48 51
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The model of crop trees in mixed spruce, fir and
beech stands as a variant of model for tree
species and production goal
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The cultivation of the trees of selective quality
can be carried out by two following methods

• method of the promising trees - consists in
  deliberate support of a certain number of
  promising trees by positive crown selection.
  Number of PT decreases during the period of
  thinnings and at the least from the second half
  of rotation age it should be more or less stable
• method of target (crop) trees - is based on the
  fact that in partial period of stand development,
  from small pole-stage stand at the beginning to
  timber forest at the end, as object of
  silvicultural attention is more or less an stable
  number of trees of the same qualitative (crop)
  trees

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The scheme of development of number of trees N
for promising trees and crop trees
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The scheme of the regulation of the spacing of
the trees of selective quality
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Average model spacing and number of crop trees
per hectare in pure stands are as follows
(L.Štefancík, 1988)
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Development of crop trees on PRP Jalná after
38-years of systematic tending
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Conclusion

• the free crown thinning contains in its
  conception many requirements from principles of
  ecologically oriented silviculture (for example,
  cultivation of suppressed level of the stand,
  differentiation of stand vertical profile)
• It can be concluded that above-mentioned thinning
  method appears to be also very perspective for
  conversion of stands with age classes
  (clear-cutting) into selection forest.

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Thank you for your attention