Kristina Mjöfors, Monika Strömgren, Hans-Örjan Nohrstedt, Annemieke Ingrid Gärdenäs. (2015). Impact of site-preparation on soil-surface CO₂ fluxes and litter decomposition in a clear-cut in Sweden. Silva Fennica vol. 49 no. 5 article id 1403. https://doi.org/10.14214/sf.1403

Keywords: boreal forest; soil disturbance; soil respiration; carbon stock; needle decomposition; coarse root decomposition

Highlights: Disturbances of the soil did not lead to higher CO₂ emissions from the soil; Heavy mixing of the soil lead to lower CO₂ emissions from the soil; Buried needles and coarse roots decomposed faster than those on the surface; Abundance of δ¹⁵N decreased in needles and roots after site preparation.

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Boreal forest soil contains significant amounts of organic carbon. Soil disturbance, caused for example by site preparation or stump extraction, may increase decomposition and thus lead to higher CO₂ emissions, contributing to global warming. The aim of this study was to quantify responses of soil-surface CO₂ fluxes (R_s) and litter (needle and root) decomposition rates following various kinds of soil disturbance commonly caused by mechanical site preparation and stump harvest. For this purpose four treatments were applied in a clear-cut site in central Sweden: i) removal of the humus layer and top 2 cm of mineral soil, ii) placement of a humus layer and 2 cm of mineral soil upside down on top of undisturbed soil, forming a double humus layer buried under mineral soil, iii) heavy mixing of the humus layer and mineral soil, and iv) no disturbance (control). R_s measurements were acquired with a portable respiration system during two growing seasons. To assess the treatments’ effects on litter decomposition rates, needles or coarse roots (Ø = 6 mm) were incubated in litterbags at positions they would be located after the treatments (buried, or on top of the soil). The results indicate that site preparation-simulating treatments have no effect or may significantly reduce, rather than increase, CO₂ emissions during the following two years. They also show that buried litter decomposes more rapidly than litter on the surface, but in other respects the treatments have little effect on litter decomposition rates.

Mjöfors, Swedish University of Agricultural Sciences (SLU), Department of Soil and Environment, P.O. Box 7014, 150 07 Uppsala, Sweden E-mail: kristina.mjofors@slu.se
Strömgren, Swedish University of Agricultural Sciences (SLU), Department of Soil and Environment, P.O. Box 7014, 150 07 Uppsala, Sweden E-mail: Monika.stromgren@slu.se
Nohrstedt, Swedish University of Agricultural Sciences (SLU), Department of Soil and Environment, P.O. Box 7014, 150 07 Uppsala, Sweden E-mail: Hans-orjan.nohrstedt@slu.se
Gärdenäs, Swedish University of Agricultural Sciences (SLU), Department of Soil and Environment, P.O. Box 7014, 150 07 Uppsala, Sweden E-mail: Annemieke.gardenas@slu.se

article id 66, category Research article

Monika Strömgren, Kristina Mjöfors, Björn Holmström, Achim Grelle. (2012). Soil CO2 flux during the first years after stump harvesting in two Swedish forests. Silva Fennica vol. 46 no. 1 article id 66. https://doi.org/10.14214/sf.66

Keywords: stump removal; Picea abies; C stock; site preparation; soil C; soil disturbance; soil respiration

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One way of increasing the supply of renewable energy, thereby decreasing the use of fossil fuels, is to extract the stumps that remain after final stem harvesting. However, little is known about the environmental consequences of stump harvesting, and how ecosystem services, such as carbon sequestration, are affected by the practice. In the present paper, the effects on the soil carbon pool during the first months and years after stump harvesting in former Norway spruce stands are presented. The study was performed at two sites in mid- and southern Sweden. At both sites, the soil CO₂ flux was measured on several occasions with a portable respiration system, to compare plots on which stump harvesting had occurred, with reference plots. At one of the sites, CO₂ exchange was also followed continuously by means of eddy-covariance measurements before and after stump harvesting. Since there was no vegetation at the beginning of the study, almost all emitted CO₂ could be assumed to come from heterotrophic sources, and the soil CO₂ flux was measured. This study shows that the effect of stump harvesting on CO₂ flux or soil decomposition processes is small or absent compared to site preparation such as mounding in a short-term perspective of months and years. The long-term consequences of stump harvesting are, however, still uncertain.

Strömgren, Swedish University of Agricultural Sciences, Department of Soil and Environment, Uppsala, Sweden E-mail: monika.stromgren@slu.se
Mjöfors, Swedish University of Agricultural Sciences, Department of Soil and Environment, Uppsala, Sweden E-mail: km@nn.se
Holmström, Swedish University of Agricultural Sciences, Department of Soil and Environment, Uppsala, Sweden E-mail: bh@nn.fi
Grelle, Swedish University of Agricultural Sciences, Department of Ecology, Uppsala, Sweden E-mail: ag@nn.se

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