Pre-commercial thinning, birch admixture and sprout management in planted Norway spruce stands in South Sweden

Abstract

Early management of the regenerated seedlings shapes the future stand properties. To address these issues, pre-commercial thinning (PCT) and control treatments were applied to planted Norway spruce (Picea abies L. Karst) and naturally regenerated birch (Betula pendula Roth., Betula pubescens Ehrh.) stands in forest experiments in southern Sweden (lat. 56–57 N) containing 1.1–5.5 m tall saplings. The treatments were retention of 1000 or 2000 stems ha⁻¹ of Norway spruce, with no birch or birch at 1000 stems ha⁻¹. Treatments were replicated with and without annual removal of birch sprouts from stumps. The periodic annual increment (PAI) over five years was calculated for total stand volume and individual trees. The mean PAI of dominant trees was significantly higher both following all PCT treatments than controls, and following low rather than high-density PCT. Birch retention did not affect growth of the dominant trees but PAI was lower in plots with uncontrolled sprouting. The PAI of birch was significantly higher in low-density Norway spruce plots than in control plots and the high-density plots. The treatment response was significant even in stands with initial heights of only 1–2 m.

Keywords:

• Picea abies
• Betula
• mixed-species forest
• tending
• cleaning

Acknowledgements

We thank the staff at Asa and Tönnersjöheden Experimental Forests for the work with trial establishment, maintenance and mensuration.

Disclosure statement

No potential conflict of interest was reported by the author.

Funding

This study was financed by Future Forests, a multi-disciplinary research program supported by the Foundation for Strategic Environmental Research (MISTRA), the Swedish Forestry Industry, the Swedish University of Agricultural Sciences (SLU), Umeå University and the Forestry Research Institute of Sweden (Skogforsk).

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/02827581.2015.1055792.