Browsing by Author "Poutamo, Helinä"

Peatlands are significant pools of carbon and nitrogen. Forestry-drained peatlands have lower methane emissions than undisturbed peatlands, but emissions of carbon dioxide and nitrous oxide increase after ditching. The effect of ditching on the emissions of peat is stronger on nutrient-rich peatlands than on nutrient-poor peatlands. However, the growing vegetation and wood production form a large carbon sink. So far, forestry-drained peatlands have mainly been carbon sinks in Finland. There are 4.6 million hectares of forestry-drained peatlands in Finland. Ditching peatlands for forestry started in the beginning of the 20th century, and was on its height from 1960s to 1980s. Forestry-drained peatlands are reaching maturity now, but there is little knowledge about the effect of forest management practices on greenhouse gas emissions from forestry-drained peatlands. The purpose of this study is to investigate the effect of logging residues on emissions of carbon dioxide, methane and nitrous oxide from forestry-drained peatlands. Greenhouse gas emissions were measured from the nutrient-rich peatland Lettosuo in Tammela that was drained for forestry in 1969. In early spring of 2016, dominant pine trees were harvested to make room for spruce undergrowth. During the harvest, the harvester formed piles of logging residues on its tracks to avoid erosion of the soil. Five plots were established and measurements taken with the closed-chamber method during 2016-2017. On each of the five plots, two chamber collars were installed on the machine’s tracks, full of logging residues, and other two collars were installed outside of the tracks with little to no logging residues. In addition to greenhouse gas emissions, the dry mass of the logging residues, temperature and groundwater level were measured. Carbon dioxide emissions from residue-covered collars was measured at 0.81–0.88 g m-2 h-1. The fluxes were 1.5-2 times larger than on the control collars (0.40–0.54 g m-2 h-1). A kilogram of logging residues raised the emissions by 0.10 ± 0.01 g m-2 h-1. Compared to the dry mass of branches, the dry mass of needles increased the emissions fourfold. On plots 1-4, the collars installed in the groove of the harvester’s tracks were the only sources of methane by 0.0055 mg m-2 h-1. The methane flux of the other collars varied between -0.0035 and 0.0136 mg m-2 h-1. A kilogram of logging residues raised methane fluxes by 0.003 ± 0.001 mg m-2 h-1. Again, the effect of needles was quadruple as compared to branches. Plot #5 was investigated separately due to the Eriophorum vaginatum that had grown inside the collars. On all plots, nitrous oxide emissions didn’t significantly differ from collar to collar, even though emissions measured from logging-residue covered collars (0.20–0.30 mg m-2 h 1) were two to three times larger than on the other collars (0,10 mg m-2 h-1). Logging residues and the mechanical impact of the harvester on the peat soil increase emissions of carbon dioxide and methane. Emissions of nitrous oxide also increase, but the variance of measured emissions and the small sample size rendered the results statistically insignificant.