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- Dahlgren Lidman, Felicia, et al.
(author)
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Management of spontaneously regenerated mixed stands of birch and Norway spruce in Sweden
- 2021
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In: Silva Fennica. - : Finnish Society of Forest Science. - 0037-5330 .- 2242-4075. ; 55
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Journal article (peer-reviewed)abstract
- Timber production and profitability were evaluated for spontaneously-regenerated mixtures on two formerly clearcut areas. The abandoned areas developed into birch-dominated (Betula pendula Roth and Betula pubescens Ehrh.) stands with successional ingrowth of Norway spruce (Picea abies (L.) H. Karst.). An experiment with randomized treatments within blocks was established, using three management strategies and one unthinned control, resulting in variation in optimal rotation age, merchantable volume and species composition. The management strategies were evaluated based on total production (volume) by using measured growth data 42 years after clearcutting and the modelled future stand development. The long-term effects of spontaneous regeneration and management strategies were evaluated based on land expectation value (LEV) and compared with a fifth management strategy using artificial regeneration and intense thinnings. 12 years after treatment, at a stand age of 42 years, the unthinned control had produced the highest total stem volume. At interest rates of 2% or higher, the unmanaged forest was an economically viable strategy, even compared to an intensive management strategy with a preferred merchant-able timber species. Interest rates clearly impacted the profitability of the different management strategies. This study shows that when spontaneous regeneration is successful and dense, the first competition release can have a high impact on the development of future crop trees and on the species mixture.
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| 2. |
- Dahlgren Lidman, Felicia
(author)
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Natural regeneration and management of birch
- 2022
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Doctoral thesis (other academic/artistic)abstract
- This thesis offers guidance for those who want to naturally establish, maintain and manage birch in monocultures and mixed stands. Silver and downy birch are the most common broadleaf tree species in northern Europe. In Sweden, the two species together make up approximately 12% of the standing forest volume. This thesis presents results from four studies (papers I - IV), with the aim to increase the level of knowledge about establishment and regeneration of birch, management of naturally regenerated birch in pure and mixed stands, and the distribution of birch over Sweden. The studies were based on experimental data from field trials, survey data from practical forestry, Swedish national forest inventory data and predictive modelling. On dry soil, mechanical site preparation is necessary in order to get a successful regeneration of birch; in wet soil moisture conditions, natural regeneration of birch will appear without effort. It is possible to manage the birch regeneration success if the soil scarification is adapted to the soil moisture conditions (paper I). The proportion of silver and downy birch varied in Sweden’s young forests, and the temperature sum explained most of the variation (paper II). In dense, naturally regenerated stands of birch and Norway spruce, pre-commercial thinning (PCT) had a significant impact on the development of the future stand, and there are several profitable management strategies for the owner of this type of stand (paper III). The proportion of birch tends to decrease after canopy closure in mixtures of Norway spruce with stand age in southern Sweden, regardless of thinning (paper IV). Active forest management is key, in order to maintain the proportion of birch over the full rotation period. In conclusion, this thesis offers knowledge that can contribute to a more varied forestry, and forestry with a greater element of broadleaf trees.
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| 3. |
- Holmström, Emma, et al.
(author)
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Keeping mixtures of Norway spruce and birch in production forests: insights from survey data
- 2021
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 36, s. 155-163
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Journal article (peer-reviewed)abstract
- Admixtures of birch in Norway spruce plantations are being promoted as a means to increase habitat and species diversity. The implications of this mixture were analysed with regional survey data from southern Sweden. Permanent sample plots from the Swedish National Forest Inventory (NFI), with Norway spruce and admixture of birch, were used to describe the temporal trends in the admixture, regarding species composition and competitive strength. Observations from thinned plots show a higher harvest removal in birch (35%) than for Norway spruce (19%). Observations without thinnings in the period before measurement showed that individual birch tree growth was lower compared to Norway spruce and it decreased even more with increasing stand age and competition. In addition, a complementary field survey, with multiple distributed sample plots in each stand, was used to detect within-stand variation of species composition and density. Although within-stand heterogeneity was larger in mixed stands in terms of species composition, it was not different from Norway spruce monocultures in terms of stand density. These two surveys show that the admixture of birch, for several reasons, decreases over stand age and although birch increases tree species diversity, it does not necessary imply a change in density.
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