Thinning as a tool of close to Thinning as a tool of close to nature forestrynature forestry

Igor Štefančík

Forest Research Institute, Zvolen

Slovakia

“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.

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.

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)

• 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 (Schädelin´s qualitative thinning, French thinning, Danish thinning, and so on), which take into account also the suppressed layer of the stand canopy

Conception of free crown thinning

• developed in Slovakia by Prof.Dr.L.Štefančík for tending of beech (broadleaved) stands.

• this method can also be applied in mixed (spruce-fir-beech) stands.

1929 - 2002

• 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).

Silvicultural analysis of the free crown thinning Method of selection, intervention

Objective of intervention in the stand component (growth class)

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)

- 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 - sanitary condition; to increase stand resistance

Relative maturity

- tree species; to increase production of economically desirable tree species

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

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.

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

number N

pcs. ha-1

+ ++

average Volume of wood with d1.3 > 7cm

under bark

spacing S

(m)

diameter d1,3

(cm)

total venner logs

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

The model of crop trees in mixed spruce, fir and beech stands as a variant of model for tree species and production goal

Characteristic Tree species Variant (percentage of beech crop trees) 1

(30 %) 2

(40 %) 3

(50 %) Number of trees N.ha-1

coniferous trees beech Together

170-180 70-80

240-260

135-145 85-95

220-240

100-110 100-110 200-220

Average spacing (m) coniferous trees beech deciduous-coniferous

6.0 8.0 6.6

6.5 7.3 6.8

7.0 6.8 6.9

Minimal spacing (m) coniferous trees beech deciduous-coniferous

4.2 5.6 5.0

4.2 5.6 5.0

4.2 5.6 5.0

Target diameter d1,3 (cm) for dominant tree species Altitudinal forest zone Site Target diameter d1,3 (cm) spruce fir beech 5th fir-beech acid

fertile 41 44

36 44

29 34

6th spruce-beech-fir fertile 37 39 31

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

The scheme of development of number of trees “N” for

promising trees and crop trees

The scheme of the regulation of the spacing of the

trees of selective quality

Average model spacing and number of crop trees per hectare in pure stands are as follows (L.Štefančík, 1988):

Tree species Spacing (m) Number of trees per hectare Spruce, fir, pine Larch Oak, beech, other hardwoods Poplar – ligniculture Intense culture

5.0 – 6.0 6.0 – 7.0 7.0 – 8.0 6.0 – 6.5 4.0 – 5.0

300 to 400 200 to 300 150 to 200 230 to 270 400 to 600

Development of crop trees on PRP Jalná after 38-years of systematic tending

Plot Age (years)

Number of trees

Volume of timber to the top of 7 cm o.b.

Mean diameter d1.3 (cm)

(per 1 ha) (m3/ha) (% from main stand)

dg range

H 74 172 254.8 64.8 36.1 27 - 45 C 74 120 156.5 28.3 33.2 25 - 46 O 74 96 92.4 17.8 29.8 24 – 40

Model 110-130 168 397.0 79.0 43.0 - Explanatory notes: H – plot with the free crown thinning, O – plot without treatment (control), C – plot with heavy low thinning (C degree according to German forest research institutes in 1902)

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.

Thank you for your attention