The influence of anthropogenic land use on Finnish peatland area and carbon stores 1950-2015

This study presents a new data synthesis of Finnish peatland area and carbon (C) store in peat from 1950 to 2015. We present updated results from the most comprehensive compilation of Finnish peat soil properties with associated C accumulation rates from undrained mires and C sources from different forms of anthropogenic land use. Since 1950, different forms of land use of Finnish peatlands have reduced the total peat C store by 3-10 %, approximately 172-510 Tg. The most significant C losses have occurred from forestry-drained peatlands, but significant losses have also occurred from agricultural peat soils, peat extraction, and other forms of peatland exploitation such as building water reservoirs. However, the C accumulation of undrained mires and especially the increased biomass production of drained peatlands have partly compensated for the anthropogenic C losses. The total C store of peatland vegetation biomass (trees, seedlings, ground vegetation, detritus and below-ground roots) was estimated to have increased by 92 Tg due to intensive peatland drainage. The present total C store of Finnish peatland ecosystems was estimated at 5618 Tg, which includes 5079 Tg as peat. The total C store estimate is approximately 1-7 % lower compared to the 1950s. Today, the undrained mires still represent a significant national C sink, with the rate of C sequestration estimated at 0.82 Tg [yr.sup.-1]. However, across all land uses the present peat soil is a C source by 3.7-10.0 Tg [yr.sup.-1]. Significant anthropogenic C losses from peat soil underline the urgent need for sustainable C management of all peatlands, including the preservation of the C store in existing natural mires, stopping land clearing on undisturbed organic soils, and improving the peatland hydrology by restoration to create long-term C sinks especially within the large unproductive drainage area and northern aapa mire area. KEY WORDS: carbon, drainage, Finland, land use, peatlands