Indications that site preparation increases forest ecosystem carbon stocks in the long term

ABSTRACT

Mechanical site preparation (MSP) causes a mixing disturbance of the soil, which may increase decomposition of soil organic matter and subsequent carbon (C) dioxide emissions to the atmosphere. MSP also promotes the establishment and growth of tree seedlings, and hence ecosystem C fixation. However, there are uncertainties regarding the net effects of MSP on C stocks at the ecosystem scale. To assess decennial effects of MSP on ecosystem C stocks, C stocks in soil, ground vegetation and trees at three experimental forest sites with Pinus contorta, Pinus sylvestris and Picea abies in Sweden were sampled and measured for ca. 25 years in a control and after three MSP treatments: disc trenching, mounding and ploughing. After 25 years, all of the MSP treatments resulted in larger ecosystem C stocks than the control treatment due to positive effects on the tree biomass C stock. The tree C stock was highest after ploughing, intermediate after mounding or disc trenching and lowest in untreated control plots at all experimental sites. The MSP treatments did not affect the soil C stocks down to 30 cm. We recommend mounding or disc trenching to promote C sequestration as they disturb sites’ ecological, aesthetic and recreational values less than ploughing.

KEYWORDS:

• Carbon sequestration
• ecosystem
• tree biomass
• soil
• disc trenching
• mounding

Acknowledgements

We wish to thank the staff from the Unit for Field-based Forest Research at Tönnersjöheden and Siljansfors, SLU, for the inventory of tree biomass in both sites and soil sampling in Fläda; the staff of Soil Chemistry Laboratory at the Dept. of Soil and Environment (SLU) for chemical analyses; Mikael Andersson Franko and Claudia von Brömssen (both SLU) for their advice and helpful suggestions regarding statistical analysis and Andreas Eriksson (Swedish Forest Agency) for unpublished data of different types of site preparation. Finally, we thank Sees-editing Ltd for language checking and the two anonymous reviewers for their constructive comments.

Additional information

Funding

The study was part of the research programme “Tree-stump harvesting and its environmental consequences” at the Swedish University of Agricultural Sciences with grants from the Swedish Energy Agency (P30468-1), the Faculty of Natural Resources and Agricultural Sciences at the Swedish University of Agricultural Sciences (SLU) and a consortium of forest companies. Additional funding was received from the strong research environment IMPRESS (the Swedish Research Council Formas 2011–1747) and the Royal Swedish Academy of Agriculture and Forestry (GFS2015-0086).