Spruce Forest on Drained Peatlands Bad for Climate
Sweden’s drained peatlands release as much greenhouse gas as road traffic does. It would be better for the climate if these areas were allowed to return to their natural state or crop plants better suited to wet conditions. According to a recent study from The University of Gothenburg, cultivating willow or reed canary grass offers a better financial return for the landowner than the forestry currently practiced.
Forestry on drained peatlands is a major source of greenhouse gases.
“If drainage channels were not to be cleared anymore and outflow of water instead blocked, the peat decomposition would slow considerably,” says Åsa Kasimir, researcher at the Department of Earth Sciences at The University of Gothenburg.
Together with her fellow researchers, she has sought to find out how a changed land use can affect the level of greenhouse gas production in the ecosystems, from Spruce forest, to cultivating bioenergy crops, to conversion to wetlands.
The study, published in Global Change Biology, shows how large the reduction of green-house gas emissions from drained peatlands now used for timber production can be.
“We have calculated that drained nutrient-rich, peatland, comprising two percent of Sweden’s productive forestry land, emits 16 million metric tons of carbon dioxide equivalents resulting from the decomposition of organic material in the soil. Emissions from road traffic is only slightly higher at 17 million metric tons. Our study shows that the soil needs to be wetter to reduce emissions and it would then be possible to grow bioenergy crops or re-vert to natural wetland,” says Åsa Kasimir, researcher at the Department for Earth Sciences.
Higher water levels reduce peat decomposition
According to the study, growth rate of willow and reed canary grass could be as large as for spruce, even at wetter soil. And the wetter the soil, the less peat decomposition. Compared with Spruce, Willow cropping decreases peat decomposition by 50%, and by 75% when cropping Reed Canary Grass, and if restored to wetland decreases by 85%.
The study shows that the climate impact from the land is lowest when water levels are between 10 to 20 cm below the ground surface.
The model study was based on measurement data from the research station Skogaryd, situated between Uddevalla and Vänersborg, where spruce forest grow on drained peatlands. The research estimated greenhouse gas balances in the ecosystems, between soil and vegetation, over a period of 80 years.
More ecological and profitable to grow willow and reed canary grass
By a cost-benefit analysis over a forest rotation period of 80 years the researchers found that land owners profit only counterbalance the climate cost at a carbon-price about 20% of the current Swedish carbon tax.
“However landowners’ wallet does only see the profit made from products which ends up being twice as large with willow and reed canary grass compared to spruce forest. So even without any public support, wetter soil with bioenergy crops should be obvious,” says Åsa Kasimir.
Her conclusion is that it is a need to change how drained nutrient-rich peatlands are used.
“Now when much of the forests on the drained peat soils are close to harvest these areas should not be replanted with spruce, but instead made wetter and produce plants adapted to wet conditions or revert to wetland which doesn’t deplete peat resources,” says Åsa Kasimir.
Article Name: “Land use of drained peatlands: greenhouse gas fluxes, plant production and economics”. Authors: Åsa Kasimir, Hongxing He, Jessica Coria, Anna Nordén.
Åsa Kasimir, Department of Earth Sciences, University of Gothenburg
Email: email@example.com, Phone: 031-786 19 60 , Cell: 0704-91 13 61
Image 1: Åsa Kasimir, Ebba Klemedtsson, Photographer.
Image 2: Spruce forest on drained peatland in Skogaryd.