What should the silviculture care for substitutional stands of European larch look like
The European larch is a valuable tree species for creating mixed forest stands. Currently, it represents around 3.9% of our forests, but there is a proposal to increase its representation to 5%. One of its advantages is its ability to grow in a wide range of habitats, from lowlands to lower mountain locations. Because of its pioneering growth strategy, it can be used as a preparatory woody plant on areas where trees have been cleared due to disasters, and it rejuvenates and grows well in those areas. Its deciduous needles make it relatively resistant to pollution, which is why it has been used to establish stands of substitutional trees.
Photo: Young larches in mixture with Scots pine, author Jan Řezáč
In the 1970s and 1980s, substitutional tree species were planted in mountain and foothill areas heavily affected by smog, particularly in the Ore and Jizera Mountains. The aim was to maintain the continuity of the forest environment and, in the case of larch, to partially replace the wood production of dead spruce stands. However, these stands were not meant to be a permanent solution, but rather a preparatory phase to establish stable and more diverse forest stands using tree species suitable for the habitat.
Foresters typically create new larch stands as smaller monoculture stands. The management of these stands mainly involves maintaining and enhancing their non-production functions, and improving the stability and quality of production in cases where the stands are productive.
The research conducted by scientists from the Opočno Research Station, VÚLHM, v. v. i., aimed to assess the condition and other aspects of these stands. The main objective was to evaluate the impact of silvicultural interventions on the growth of mixed larch stands in the specific conditions of substitutional tree stands.
Photo: Young larches in mixture with Norway spruce, author Jan Řezáč
The findings were published in the article titled „The effect of thinning on the growth of a substitute forest stand of European larch (Larix decidua Mill.) “ /Vliv výchovných zásahů na růst náhradního porostu modřínu opadavého/, which appeared in the journal “Reports of Forestry Research in February 2024 (2/2024 issue). The article was produced as part of the NAZV grant project QK21010335 Possibilities of using deciduous larch in Czech forests under the impact of GKZ /Možnosti využití modřínu opadavého v českých lesích pod dopadem GKZ/.
The experiment took place in an 11-year-old European larch forest with trees averaging about 7 meters in height. The forest was originally planted through artificial regeneration in 2001 at a former forest nursery site. Approximately 2,500 trees were planted in a regular pattern covering one hectare. The experimental forest is located in the Ore Mountains, within the municipality of Božetín, at an altitude of 560 meters. Scientists analysed dendrometric data from the establishment of the experiment up to the age of the forest, which was 29 years.
It is crucial from a silviculture perspective to meet the light requirements of larch trees. Larch does not tolerate shading from above or strong lateral shading. Therefore, it is important to timely release promising larch individuals and pre-sprouts with long and flexible crowns.
Photo: There is an overgrown larch stand on the right side of the road, taken by Jan Řezáč
If silviculture interventions are not implemented, the slenderness quotient of the stem decreases quickly, and the crowns shorten rapidly. Properly chosen silviculture for a larch stand should result in the development of open crowns that are at least 1/3 of the tree’s height.
In their conclusion, the scientists summarized their findings:
Silviculture interventions in pure larch stands resulted in accelerated tree growth and improved stability by reducing slenderness.
The silviculture variant that included one intervention at the age of 11 years resulted in trees with a more favorable slenderness ratio compared to the control group. However, it did not effectively maintain sufficiently long crowns (at least 1/3 of the tree height). The absence of a second intervention led to a significant decrease in tree thickness growth during the second half of the experiment, between 20 and 29 years of stand age.
Photo: Mature mixed forest, larch with broadleaves, author Jan Řezáč
The variant involving two silviculture interventions at the ages of 11 and 20 years produced satisfactory results in terms of tree slenderness and maintaining desirable crown lengths. However, a significant intervention at the age of 20, resulting in a stand reduced to only 320 trees per hectare, is likely to lead to production losses compared to less intense silviculture intervention variants.
The main advantage of implementing strong silvicultural intervention is not just about increasing production, but also about stabilizing the larch stand structure as a foundation for converting replacement forest stands into stands with a wider variety of species and more suitable habitats. It is recommended to begin introducing underplantings with species like European beech or silver fir starting from the second phase of the stand’s development, after the second strong intervention.
In substitute larch stands, scientists recommend applying early silvicultural interventions at an upper stand height of 5 m to strengthen the stand skeleton and increase the vitality of the released trees by maintaining sufficiently long crowns.
Scientists consider implementing two silviculture interventions to be an effective method to ensure that about 320-350 trees per hectare remain at the age of 20 years. It is acceptable to experience some reduction in volume production in stands of substitute tree species due to these interventions.
Further silviculture measures in these stands should be aimed at transforming them into more species-diverse stands, with larch serving as a preparatory tree species. It is suitable for mixtures with beech, oak, linden, or hornbeam.
Paper „Vliv výchovných zásahů na růst náhradního porostu modřínu opadavého“ /The effect of thinning on the growth of a substitute forest stand of European larch/ can be downloaded here.
Authors: David Dušek, Jiří Novák, VÚLHM, v. v. i., Research Station Opočno, e-mail: dusek@vulhmop.cz
Prepared from the original by Ing. Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz
Introductory photo: Mature larches at the edge of the forest, author Jan Řezáč