Research findings on fast-growing broadleaves – annual report Trees For Me

Summary of the Trees For Me annual report 2025:

Research

Work package 1 – Tree breeding

• The infrastructure for tree breeding has been developed during the year, for example through four new progeny trials with 14.000 planted seedlings of silver birch in northern Sweden, the first trials of its kind in the region since 1995.
• The research focused on genomic selection has resulted in the first genomic prediction models for birch breeding in Sweden during 2026.
• Results from research on accelerating breeding cycles show that exposing birch seedlings to continuous light strongly stimulates birch flowering, particularly female flowers, and induces more viable seeds.

Work package 2 – Silviculture

• Analyses from three growing seasons (2023–2025) are onging related to plant production and regeneration with containerized birch seedlings across Swedish climatic regions. These experiments investigate the effects of container size, planting date, site preparation method, fertilisation and planting timing relative to clear-cut age.
• Results show that spruce-dominated mixtures can achieve similar growth and improved economic outcomes compared with spruce monocultures.
• A path-planning tool, named TerraTrail, has been developed to optimise driving routes for mechanised planting systems, in collaboration between Bracke Forest and Luleå University of Technology.
• Results show that birch seedlings are only mildly affected by pine weevils and other weevils, and that mechanical protection treatment with Hylonox has a positive effect on the survival of the seedlings.

Work package 3 – Material and energy

• Results show that producing timber from birch and harvesting birch for energy biomass in the first thinning of birch-spruce mixed stands can generate positive net revenues, especially on medium-fertile sites.
• Research also shows that poplar biomass exhibits ash characteristics comparable to conventional forest fuels from conifers and birch, indicating good suitability for thermochemical conversion to fuels, bio-oil or biochar.
• A kinetic model has been developed to design and optimise biomass conversion processes, including when using fast-growing broadleaves.

Work package 4 – Societal transitions

• Survey results indicate broad agreement among stakeholders in southern Sweden that expansion of fast-growing broadleaves should continue, although opinions differ regarding the pace and scale of change. Key barriers highlighted by the stakeholders include limited coordination between supply and demand actors and insufficient information about existing broadleaf resources.
• Analysis of a national survey targeting private forest owners shows that both contextual factors (such as location and landscape) and psychological factors (such as beliefs and emotions) influence interest in planting improved birch. The survey also showed that the willingness to plant hybrid aspen and poplar in central and southern Sweden is relatively low, but that knowledge of the tree species can increase interest.

Work package 5 – Environmental impacts

• Results from a study on improved birch, with approximately 20 % higher productivity compared to naturally regenerated birch over a 50-year rotation period, show that both improved growth and increased production of longer-lived products, such as sawn wood, can contribute to reducing global warming impacts across different time perspectives.
• A second study compared the climate impact of replacing Norway spruce with birch on sites with different productivity levels. Preliminary results indicate that on low-productivity sites replacing spruce with improved birch, particularly when used for long-lived wood products, can reduce climate impacts. On highly productive sites, spruce remains more favourable from a climate perspective. The results highlight the importance of site-specific management decisions.
• Within the biodiversity research experiments were conducted in 48 stands of birch, poplar and hybrid aspen across southern Sweden. Birch stands showed the highest lichen species richness, although all tree species hosted species of conservation interest.

Education and collaboration

Trees For Me’s PhD students and researchers continuously teach about sustainable forestry, materials and energy to students at the universities enrolled with the centre, and to officials and practitioners in the forest and energy sector.

During the year, collaboration activities to reach out with knowledge about fast-growing broadleaf trees has been further developed, for example through continued webinars and excursions in collaboration with the Swedish Forest Agency and initiation of a collaboration project with Södra to spread research-based knowledge in forest owners' planning tools.