Greenhouse gas and energy fluxes in a boreal peatland forest after clearcutting

Abstract

<p><strong>Abstract.</strong> The most common forest management method in Fennoscandia is rotation forestry including clearcutting and forest regeneration. In clearcutting, stem wood is removed and the logging residues are either removed or left on site. Clearcutting changes the microclimate and vegetation structure at the site, both of which impact the site's carbon balance. Peat soils with poor aeration and high carbon (C) densities are especially prone to such changes, and significant changes in C stocks and greenhouse gas exchange can be expected. We measured carbon dioxide (CO<sub>2</sub>) and energy fluxes with the eddy covariance method for two years (April 2016–March 2018) on a peatland drained for forestry. After the clearcutting, we observed a significant rise (23 cm) in the water table level. The site was also a large CO<sub>2</sub> source (first year: 3086 ± 120 g CO<sub>2</sub> m<sup>−2</sup>yr<sup>−1</sup>, second year: 2072 ± 141 g CO<sub>2</sub> m<sup>−2</sup> yr<sup>−1</sup>) after the clearcutting. These large CO<sub>2</sub> emissions resulted from the collapse of gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation. During the second summer (June–August) after the clearcutting, GPP had already increased by 96 % and total ecosystem respiration decreased by 14 % from the previous summer. As a result, net CO<sub>2</sub> emissions decreased during the second summer after clearcutting compared to the first one. The Bowen ratios were different in 2016 and 2017, starting at 2.6 in May 2016 and decreasing to less than 1.0 in August 2016, while in 2017 it varied mostly within 0.6–1.0. This was due to a 33 % decrease in the sensible heat flux and a 40 % increase in the latent heat flux from the 2016 values, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO<sub>2</sub> and energy fluxes, we measured methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) fluxes with manual chambers. After the clearcutting, the site turned from a small CH<sub>4</sub> sink into a small source and from N<sub>2</sub>O-neutral to a significant N<sub>2</sub>O source. Compared to the large CO<sub>2</sub> emissions, the global warming potential (GWP<sub>100</sub>) of the CH<sub>4</sub> emissions was negligible. Also, the GWP<sub>100</sub> due to increased N<sub>2</sub>O emissions was less than 10 % of that of the CO<sub>2</sub> emission change.</p>

Shallow groundwater inhibits soil respiration and favors carbon uptake in a wet alpine meadow ecosystem

“…These results confirmed that nearly-saturated conditions largely suppressed soil respiration and further caused a large carbon sink. This finding was consistent with the situations in several wet ecosystems, such as tropical peatlands, northern peatlands, and Arctic tundra (Knowles et al 2015;Korkiakoski et al 2019;Hoyt et al 2019). For example, Knowles et al (2015) reported that in a wet tundra ecosystem in the Colorado Rocky Mountains there was a significantly negative relationship between SM and soil respiration when soil moisture was above 0.38; they explained this result through the fact that soil respiration switched from moisture-limited to oxygen diffusion-limited with increasing SM.…”

“…These ecosystems generally act as a carbon sink (Kato et al 2006;Li et al 2016;Scholz et al 2018), which however is expected to be reduced and potentially turns into a carbon source in response to future warming, due to the accelerated soil carbon decomposition (Virkkalaet al 2017;Ganjurjav et al 2018;Sun et al2019). Many previous studies reported that climate warming and human activities will change the soil hydrologic conditions and further affecting the soil carbon dynamics of several cold ecosystems, including Arctic tundra, northern peatlands, mires, and bogs (Ise et al2008;Dorrepaal et al 2009;Dinsmore et al 2010;McVeighet al 2014;Schädel et al 2016;Drollinger et al2019;Gockede et al 2019;Korkiakoski et al 2019;Stover & Henry 2019;Swindles et al 2019). However, the mechanisms by which the soil hydrological conditions, such as the shallow groundwater level, affect carbon exchanges in alpine meadow ecosystem are poorly understood.…”

Bayesian methods applied for ecosystem model calibration and uncertainty source estimation

“…Forest management in Finland is a strong modifier of ecosystem carbon budgets and usually an unaccounted source of uncertainty in future predictions. The harvesting intensity defines the impact to the ecosystem carbon exchange (Korkiakoski et al, 2018). According to Kalliokoski et al (2018), the future forest productivity was predicted to increase towards the end of the century.…”

The short-term effect of partial harvesting and clearcutting on greenhouse gas fluxes and evapotranspiration in a nutrient-rich peatland forest

“…Data for the clear-cut site for two post-treatment years are available through Zenodo (10. 5281/zenodo.3384791, Korkiakoski et al, 2019b). WTL and chlorophyll fluorescence data are made available here.…”