Growth and thinning effects during a rotation period of hybrid aspen in southern Sweden

Abstract

Hybrid aspen is an interesting tree species for wood production in northern Europe. In this study we examined growth dynamics over the whole rotation period. Height and diameter development, as well as annual growth of stem volume and stem biomass, were repeatedly recorded in 14 planted and 2 root sucker stands, aged up to 26 years, in southern Sweden. A main aim was to study the productivity level for hybrid aspen forestry with an expected rotation period of about 25 years. The study verified earlier prognoses, showing a mean annual increment (MAI) of 19.5 m³ of stem wood ha⁻¹ yr⁻¹ after 25 years. This corresponds to a dry weight of stem biomass of 7.2 tons dry matter (DM) ha⁻¹ yr⁻¹. Maximum MAI was still not reached after 25 years, although the growth curve was flattening out. If branch biomass is included, MAI is estimated to about 9 tons DM ha⁻¹ yr⁻¹ and further improvements in growth is expected by using the best genotypically selected clones available. Results from three different thinning regimens showed that thinning intensity provided significantly larger diameter growth, while no significant yield effects were seen among the thinning regimens.

Keywords:

• height growth
• mean annual increment
• Populus tremula × Populus tremuloides
• stem diameter growth
• Sweden
• thinning effects
• volume growth and biomass production

Acknowledgements

The authors thank the technicians at the Forestry Research Institute of Sweden, Gudmund Ahlberg, Sten Nordlund, Frosten Nilsson and Johan Malm for their patient and accurate work with height and diameter measurements. The authors also thank Rose-Marie Rytter for valuable comments on the manuscript.

Funding

This study has been supported by the Swedish Energy Agency, the Swedish Tree Breeding Association, and the framework programme of the Forestry Research Institute of Sweden from the time of establishment to the final assessments.

Additional information

Funding

Funding: This study has been supported by the Swedish Energy Agency, the Swedish Tree Breeding Association, and the framework programme of the Forestry Research Institute of Sweden from the time of establishment to the final assessments.