Greenhouse gas balance of forestry-drained boreal peatlands: Sinks or sources?

Non peer reviewe

Unearthing fine root production by plant functional groups in drained peatlands through in-growth cores

201

Do logging residue piles trigger extra decomposition of soil organic matter?

Logging residue piles have been suggested to markedly increase the decomposition of the underlying peat soil leading to large carbon dioxide emissions. We aimed at scrutinizing this postulate with straightforward decomposition (mass loss) measurements. For the purpose, authentic soil organic matter (humus and peat) was incubated in mesh bags under piles and at control plots. The effect of piles was assumed to result from physical (shading and insulation on soil surface) and chemical-biological (leaching of nutrients and fresh organic matter) sources. To distinguish between the two, artificial piles of inorganic matter were established to mimic the bare physical effects. Enhancement of decomposition in the soil under the real and artificial piles was assessed by measuring the mass loss of cellulose strips. Logging residue piles had clear physical effects on soil: temperatures were lowered and their diurnal variation subdued, and relative humidity at the soil surface was higher. The effect on soil moisture was also evident, but more variable, including both decreases and increases. These effects, mimicked by the artificial piles, decreased rather than increased cellulose mass loss. As the real piles, on the other hand, increased mass loss, we conclude that logging residue piles may enhance decomposition in soil due to chemical-biological mechanisms. Also the results on humus and peat mass loss indicate that piles can both increase and decrease decomposition. Consistent, remarkable increase in mass loss was not observed. Thus, our results do not support the postulate of logging residue piles dramatically increasing decomposition of soil organic matter. Rather, they hint that the effect of logging residue piles on soil is an interplay of physical and chemical-biological effects and carbon transport via roots and fungi. To fully understand and quantify these effects, vertical C fluxes between piles and soil and horizontal C fluxes within soil need to be assessed in addition to decomposition in soil and piles.Peer reviewe

The impact of logging residue on soil GHG fluxes in a drained peatland forest

Northern peatlands contain substantial reservoirs of carbon (C). Forestry activities endanger the C storages in some of these areas. While the initial impacts of forestry drainage on peatland greenhouse gas (GHG) balance have been studied, the impacts of other silvicultural practices, e.g. logging residue (LR) retention or removal, are not known. We measured the CH4, N2O and CO2 fluxes between peat soil and atmosphere with and without decomposing LR over three (2002-2004) seasons (May-Oct) following clearfelling in a drained peatland forest, along with the mass loss of LR. Seasonal average CO2 efflux from plots with LR (3070 g CO2 m–2 season-1) was twice as high as that from plots without LR (1447 g CO2 m–2 season-1). Less than 40 % of this difference was accounted for by the decay of logging residues (530 g CO2 m–2 season-1), so the majority of the increased CO2 efflux was caused by increased soil organic matter decomposition under the LR. Furthermore LR increased soil N2O fluxes over 3-fold (seasonal average 0.70 g m-2), compared to plots without LR (0.19 g m-2), while no change in CH4 emissions was observed. Our results indicate that LR retention in clearfelled peatland sites may significantly increase GHG emissions and C release from the soil organic matter C storage. This would make the harvesting of LR for biofuel more beneficial, in the form of avoided emissions. Further investigations of the sources of CO2 under logging residues are, however, needed to confirm this finding.Peer reviewe

The dependence of net soil CO2 emissions on water table depth in boreal peatlands drained for forestry

The aim of this study was to build regression models between mean water table depth (WTD, cm) and net soil CO2 emissions (g m(-2) year(-1)) using data from boreal peatlands drained for forestry. We found that net soil CO2 emissions increased linearly with increasing WTD to depths of approximately 60 cm. The regression equations differed between nutrient rich (n = 33) and nutrient poor (n = 39) study sites: net soil CO2 emissions = -115 + 12 x WTD (nutrient rich); net soil CO2 emissions = -259 + 6 x WTD (nutrient poor). These regressions can be used to estimate changes in CO2 emissions associated with changes in forest management practices.Peer reviewe

Metsäojitetun suon ilmastovaikutukset

Peer reviewe

Ojituksen vaikutus maaperän kasvihuonekaasupäästöihin

Peer reviewe

High methane emissions from restored Norway spruce swamps in southern Finland over one growing season

Forestry-drained peatlands in the boreal region are currently undergoing restoration in order to bring these ecosystems closer to their natural (undrained) state. Drainage affects the methane (CH4) dynamics of a peatland, often changing sites from CH4 sources to sinks. Successful restoration of a peatland would include restoration of not only the surface vegetation and hydrology, but also the microbial populations and thus CH4 dynamics. As a pilot study, CH4 emissions were measured on two pristine, two drained and three restored boreal spruce swamps in southern Finland for one growing season. Restoration was successful in the sense that the water table level in the restored sites was significantly higher than in the drained sites, but it was also slightly higher than in the pristine sites. The restored sites were surprisingly large sources of CH4 (mean emissions of 52.84 mg CH4 m(-2) d(-1)), contrasting with both the pristine (1.51 mg CH4 m(-2) d(-1)) and the drained sites (2.09 mg CH4 m-(2) d(-1)). More research is needed to assess whether the high CH4 emissions observed in this study are representative of restored spruce mires in general.Peer reviewe