Drainage Ditch Cleaning Has No Impact on the Carbon and Greenhouse Gas Balances in a Recent Forest Clear-Cut in Boreal Sweden

Abstract

Ditch cleaning (DC) is increasingly applied to facilitate forest regeneration following clear-cutting in Fennoscandinavia. However, its impact on the ecosystem carbon and greenhouse gas (GHG) balances is poorly understood. We conducted chamber measurements to assess the initial DC effects on carbon dioxide (CO2) and methane (CH4) fluxes in a recent forest clear-cut on wet mineral soil in boreal Sweden. Measurements were conducted in two adjacent areas over two pre-treatments (2018/19) and two years (2020/21) after conducting DC in one area. We further assessed the spatial variation of fluxes at three distances (4, 20, 40 m) from ditches. We found that DC lowered the water table level by 12 ± 2 cm (mean ± standard error) and topsoil moisture by 0.12 ± 0.01 m3 m−3. DC had a limited initial effect on the net CO2 exchange and its component fluxes. CH4 emissions were low during the dry pre-treatment years but increased particularly in the control area during the wet years of 2020/21. Distance to ditch had no consistent effects on CO2 and CH4 fluxes. Model extrapolations suggest that annual carbon emissions decreased over the four years from 6.7 ± 1.4 to 1.6 ± 1.6 t-C ha−1 year−1, without treatment differences. Annual CH4 emissions contributed <2.5% to the carbon balance but constituted 39% of the GHG balance in the control area during 2021. Overall, our study suggests that DC modified the internal carbon cycling but without significant impact on the carbon and GHG balances.

Initial Effects of Post-Harvest Ditch Cleaning on Greenhouse Gas Fluxes in a Hemiboreal Peatland Forest

“…The mechanism of the delayed herbaceous vegetation development following DC in our study remains uncertain, however, it is to be noted that the upper part of the soil profile at the site was relatively dry with a mean WTL of − 54 to − 56 cm in all our sampling locations in the two sampling years (Table A.2) which is in contrast to previous studies in boreal mineral soil forests (e.g. Tong et al, 2022) and drained peatland forests with shallower mean WTLs of − 30 to − 40 cm (e.g. Leppä et al, 2020;Lohila et al, 2011;Ojanen and Minkkinen, 2019).…”

“…To our knowledge, there is only one published study to date that explored DC effects on the forest GHG balance which was carried out in a forest clear-cut on wet mineral soil in boreal Sweden (Tong et al, 2022). This study reported insignificant effects of DC on C and GHG balances and vegetation development, despite changes in WTL due to DC.…”

“…Korkiakoski et al, 2017;Pearson et al, 2012) indicate that DC might alter the GHG balance significantly through its impact on ecosystem hydrology. While DC effects on the GHG balance have been recently explored for a forest clearcut on wet mineral soil in boreal Sweden (Tong et al, 2022), such assessment is currently lacking for the nutrient-rich peat soils in the hemiboreal region. Based on a paired experimental setup including adjacent DC and UC areas, the aim of this study was therefore to investigate the impact of post-harvest DC on GHG fluxes from clear-cut areas and ditches in a drained fertile peatland in hemiboreal Sweden.…”

Landscape‐variability of the carbon balance across managed boreal forests

“…In agreement with our findings, relatively stable RH rates were also observed in a nutrient‐limited (C:N ratio = 29) Scots pine chronosquence in hemiboreal Estonia (Uri et al, 2022 ) and in a synthesis study of RH in the boreal region (Pregitzer & Euskirchen, 2004 ). It is noteworthy, however, that our study lacks NEP data from the first few years after harvest during which considerably larger emissions have been reported by other studies conducted in boreal (Tong, Nilsson, et al, 2022 ) and hemiboreal (Tong, Nilsson, Sikström, et al, 2022 ; Vestin et al, 2020 ) clear‐cut sites.…”

On the uncertainty in estimates of the carbon balance recovery time after forest clear‐cutting

“…To argue for his concern, Lindroth (2023) complemented our dataset with one additional data point representing emissions of 610 g C m −2 year −1 during the second post‐harvest year in another boreal clear‐cut site (Tong et al, 2022). He then re‐fitted the NEP trajectory through the extended dataset and finds that SST, CCP, and OCS shifted from the 8, 18, and 138 years reported in Peichl et al (2023) to 16, 39, and 155 years, respectively.…”