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Doctoral thesis2022Open access

The greenhouse gas balance of drained forest landscapes in boreal Sweden

Tong, Cheuk Hei Marcus

Abstract

Forest drainage has been extensively used to facilitate forest growth in Fennoscandinavia. However, its impact on the ecosystem carbon (C) and greenhouse gas (GHG) balances is limited, particularly in the large area of hemiboreal and boreal Sweden. This work quantified the effect of drainage on C and GHG fluxes in the northern forests under various geographical settings, soil conditions and drainage regimes. First, this thesis describes an investigation into the initial impacts of ditch cleaning (DC) on the C and GHG balances in two forest clear-cuts using closed chamber measurements. Second, the historical drainage impacts on C and GHG balance were evaluated using eddy covariance and stream discharge measurements for a drained peatland forest and an adjacent oligotrophic mire in boreal Sweden. Results show that DC did not increase CO2 emissions. Instead, annual CO2 emission decreased after DC at the dry and fertile clear-cut site, whereas an insignificant DC effect on CO2 flux was observed at the relatively wet and infertile clear-cut site. The net CO2 uptake was recorded as being greater in the drained peatland forest relative to the adjacent mire. An effect of DC and historical drainage on mitigating strong CH4 emission and potentially increasing CH4 uptake was observed. Ground vegetation growth was identified as a primary mediator of drainage effects on the C and GHG balance, but the interaction between ground vegetation growth and drainage depended on the site soil and hydrological conditions. Other carbon and greenhouse gas components, such as flux of nitrous oxide and loss of C through discharge, did not significantly respond to drainage activities. The conclusion is that forestry drainage activities, including DC and historical activities, do not intensify carbon and greenhouse gas emissions. This work provides novel insights which can support the development of sustainable and climate-friendly forest management strategies.

Keywords

ditch cleaning; CO2; methane; peatland; boreal forest; clear-cut; eddy covariance; closed chamber

Published in

Acta Universitatis Agriculturae Sueciae
2022, number: 2022:43ISBN: 978-91-7760-960-5, eISBN: 978-91-7760-962-9
Publisher: Swedish University of Agricultural Sciences