Summary of the PhD positions

Regeneration of Scots pine

The use of Scots pine in regenerations in southern Sweden has decreased during the last 20-30 years. One contributing factor for this decrease is damage from browsing animals that may cause reduced growth and future timber quality in Scots pine plantations. New results show that Scots pine is rare to find as future crop trees in young forest stands in southern Sweden. This development is alarming, partly because Scots pine is an important tree species for the economy of forestry in the area, but also because Scots pine is an important species from a biodiversity perspective. Therefore, development of regeneration methods in order to achieve fast and secure establishment of naturally regenerated-, seeded- or planted Scots pine is one of the key questions for forest management in southern Sweden.

In order to counteract the present negative trend of Scots pine in the area, we are now looking for a PhD-student that will develop new regeneration methods for Scots pine in southern Sweden. In the PhD-project, new field experiments will be installed and data from them will be analyzed. Data from already existing experiments will also be used in the project, among other to investigate the effect of browsing and to find methods to reduce the negative effects of browsing on production and economy.

Main supervisor Urban Nilsson, SLU

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Effective regenerations

The way forest regeneration is performed depends on the goal of the future forest. Soil preparation, planting density, choice of plant material and tree species are some factors that affect the regeneration result considering both production, recreational values and environmental issues. By active choice of regeneration methods the possibilities increase for the forest owners to reach their forestry goals. Knowledge of which combinations of regeneration methods that best apply to different forestry goals and different sites is however limited.

The aim of this PhD project is to identify forest regeneration chains; combinations of methods of eg. soil preparation, plant material and tree species, that result in high plant survival and growth for different forestry goals. New information from GIS-tools, that already are used within forestry will be integrated with knowledge of the biological conditions, and in this way methods can be created that will make the regenerations sustainable regarding economy, production and the environment.

Main supervisor Karin Hjelm, Skogforsk

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Pre-commercial thinning for diverse forest types

The variety of the young forest is usually great and it is still possible influence the structure of the future forest. Thus, pre-commercial thinning is an important tool to maintain or promote the naturally established variety in the forest. One goal could be to utilize the naturally regenerated broadleaved tree or to promote the structural variation in terms of tree dimensions and the spatial distribution of tree species. There is a demand for silvicultural advices on how to promote the variation of the forest. Mixed species stands are regarded as beneficial for the biodiversity and certification standards demands a long-term admixture for broadleaves in the production forests. Silvicutural methods including multi-layered stands are also requested to complement today's clear cutting system.

We are looking for a PhD student who will study how pre-commercial thinning can be used to promote the variety of the young forest and how it will influence the stand development. The PhD student will study how naturally regenerated broadleaves can be utilized to create mixed stands. The PhD student is also going to evaluate the possibility to promote structural variety already the time of pre-commercial thinning. A part of the work will be to compile and analyse data from existing field experiments but also to establish and evaluate new field experiments.

Main supervisor Urban Nilsson, SLU

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Manage biodiversity in forest thinnings

During the past 25 years, tree retention and dead wood creation has been carried out at final felling and more deciduous trees have been retained during pre-commercial thinning in Sweden. This has changed the structure of young forest stands, soon to be commercially thinned. Today there are high-cut coarse stems, coarse old living trees and more deciduous trees in the young forests than before. Despite this, old thinning templates for homogeneous monocultures are still used. There are also new guidelines for considerations to biodiversity during commercial thinning, but these are rarely coordinated with the thinning templates.

We are offering a PhD position for development of new strategies for first commercial thinning in pine and spruce stands in Southern Sweden. The project contains two silvicultural aspects. One is about thinning aiming to keep mixed conifer/deciduous forest stands. The other is about measures and precautions directed to earlier retention of trees and biotopes. Both aspects should be evaluated with respect to wood production and biodiversity.

Main supervisor Jan Weslien, Skogforsk

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Effective silvicultural treatments

Silviculture of production stands in Swedish forestry relies on empirical models of forest development over time. The models are based on past experience and established experiments with little variation in forest stand structure and differences in environmental factors. With increased knowledge of the variation of stand variables and the variability of stand structure within the stand there are possibilities to vary the thinning strategy in different parts of the stand. It is also possible to test new techniques of remote sensing, which can be used to estimate traditional descriptive stand variables. This can provide a basis for more refined management measures at stand level.

The aim of this PhD project is to evaluate both traditional and new variables (eg leaf area) of the forest stand in order to increase the accuracy of silvicultural measures. Studies will also be made on what scale it makes sense to vary the thinning strategy. New variables that may be important for decisions about thinning and thinning strategy should describe the canopy closure, tree species composition and competition between species and local conditions of the forest stand. One purpose is also to study the smallest scale that is meaningful and financially feasible to collect and process data for variation of thinning strategies.

Main supervisor Johan Bergh, LNU

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Silviculture and wood quality in mixed stands

Sweden is mainly located in the northern coniferous zone where spruce and pine are dominating. Therefore, research and investment has been almost entirely focused on management and silviculture of conifer forests. Hardwood trees are naturally interspersed within the coniferous forests and have increased within the Swedish forests in recent years. Despite an increase in the growing stock of hardwood trees, the demand from the Swedish market exceeds the supply and the forest products industries import considerable amounts of roundwood and sawn wood each year. It is therefore essential to increase the profit derived from hardwoods and to establish their wood as a valuable resource on the markets. This requires a sound knowledge of the key wood properties influencing the suitability for value added wood conversion. To increase the interest for hardwood forestry further and provide better economic opportunities both genetic and silvicultural management must be improved.

The purpose of the PhD project is to increase our understanding on specific wood qualitative aspects of mixed (spruce and birch) forest stands in Southern Sweden. Selected birch genotypes will also be investigated. Assessing the genotypic variations in wood, fibre, stem quality and growth characteristics for different birch clones coming from ongoing trials it is of great value in introducing supplementary and more industry specific traits in the Swedish long-term breeding programme for birch. Other ongoing trials with mixed stands of various species composition and at different maturity levels will provide material for exploring the effect of management practices on stem quality and wood properties of both spruce and birch. Developed models, which connect the external to internal timber quality, will lay the scientific ground to improve the production efficiency of value added wood products from birch plantations and mixed forest stands.

Main supervisor Stergios Adamopoulos, LNU