Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declined over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands in a warmer future.

Dynamic soil models are needed for estimating impact of weather and climate change on soil carbon stocks and fluxes. Here, we evaluate performance of Yasso07 and ROMULv models against forest soil carbon stock measurements. More specifically, we ask if litter quantity, litter quality and weather data are sufficient drivers for soil carbon stock estimation. We also test whether inclusion of soil water holding capacity improves reliability of modelled soil carbon stock estimates. Litter input of trees was estimated from stem volume maps provided by the National Forest Inventory, while understorey vegetation was estimated using new biomass models. The litter production rates of trees were based on earlier research, while for understorey biomass they were estimated from measured data. We applied Yasso07 and ROMULv models across Finland and ran those models into steady state; thereafter, measured soil carbon stocks were compared with model estimates. We found that the role of understorey litter input was underestimated when the Yasso07 model was parameterised, especially in northern Finland. We also found that the inclusion of soil water holding capacity in the ROMULv model improved predictions, especially in southern Finland. Our simulations and measurements show that models using only litter quality, litter quantity and weather data underestimate soil carbon stock in southern Finland, and this underestimation is due to omission of the impact of droughts to the decomposition of organic layers. Our results also imply that the ecosystem modelling community and greenhouse gas inventories should improve understorey litter estimation in the northern latitudes.

Dissolved organic carbon (DOC) in surface waters is connected to DOC in soil solution through hydrological pathways. Therefore, it is expected that long-term dynamics of DOC in surface waters reflect DOC trends in soil solution. However, a multitude of site studies have failed so far to establish consistent trends in soil solution DOC, whereas increasing concentrations in European surface waters over the past decades appear to be the norm, possibly as a result of recovery from acidification. The objectives of this study were therefore to understand the long-term trends of soil solution DOC from a large number of European forests (ICP Forests Level II plots) and determine their main physico-chemical and biological controls. We applied trend analysis at two levels: (1) to the entire European dataset and (2) to the individual time series and related trends with plot characteristics, i.e., soil and vegetation properties, soil solution chemistry and atmospheric deposition loads. Analyses of the entire dataset showed an overall increasing trend in DOC concentrations in the organic layers, but, at individual plots and depths, there was no clear overall trend in soil solution DOC. The rate change in soil solution DOC ranged between −16.8 and +23 % yr⁻¹ (median = +0.4 % yr⁻¹) across Europe. The non-significant trends (40 %) outnumbered the increasing (35 %) and decreasing trends (25 %) across the 97 ICP Forests Level II sites. By means of multivariate statistics, we found increasing trends in DOC concentrations with increasing mean nitrate (NO₃⁻) deposition and increasing trends in DOC concentrations with decreasing mean sulfate (SO₄²⁻) deposition, with the magnitude of these relationships depending on plot deposition history. While the attribution of increasing trends in DOC to the reduction of SO₄²⁻ deposition could be confirmed in low to medium N deposition areas, in agreement with observations in surface waters, this was not the case in high N deposition areas. In conclusion, long-term trends of soil solution DOC reflected the interactions between controls acting at local (soil and vegetation properties) and regional (atmospheric deposition of SO₄²⁻ and inorganic N) scales.

Sanna Marinin hallitus on sitoutunut luonnon monimuotoisuuden tilan parantamiseen ja luontokadon pysäyttämiseen. Lupaus on äärimmäisen tärkeä. Luonnon ekosysteemien heikennys uhkaa elintärkeiden eko-systeemipalveluiden tuotantoa sekä ihmisten terveyttä, hyvinvointia ja turvallisuutta. Maailman talousfoorumi on nostanut luontokadon viiden vakavimman ihmiskuntaa uhkaavan riskin joukkoon. Myös Suomen luontotyyppien ja lajiston uhanalaisuustilanne on hälyttävä. Hallituksen kehysriihessä päätetään hallitusohjelman toteuttamisesta ja lunastetaan vuoden 2019 eduskuntavaalien lupaukset luonto- ja ilmastotoimista. Myös EU:n uusi biodiversiteettistrategia velvoittaa Suomea panostamaan luonnonsuojeluun entistä enemmän.

Sekä jatkuvapeitteistä että jaksollista metsänkäsittelyä tehdään eri voimakkuuksilla ja erilaisin hakkuutavoin. Ei ole olemassa yksiselitteistä sääntöä, jolla voitaisiin todeta, kuuluuko jokin tietty hakkuutapa jatkuva-peitteiseen vai jaksolliseen käsittelyyn (avohakkuita lukuun ottamatta). Esimerkiksi yläharvennuksia tehdään molemmissa käsittelytavoissa. Kaikkien metsänkäsittelytapojen aiheuttama häiriö on tyypillisesti sitä voimakkaampi, mitä voimakkaampi hakkuu tehdään. Avohakkuut aiheuttavat suurimman haitallisen vaikutuksen sekä luontoon että moniin metsien tarjoamiin ekosysteemipalveluihin. Yhteiskunnan kokonais-edun kannalta jatkuvapeitteisen käsittelyn osuuden lisääminen puuntuotannossa olevissa metsissä on nyky-tutkimuksen valossa kannattavaa. Jatkuvapeitteistä metsänkäsittelyä kannattaa tutkimustiedon perusteella kohdentaa etenkin puuntuotannossa oleviin metsiin, jotka sijaitsevat turvemaalla, ovat virkistyskäytössä, rajautuvat vesistöihin tai rajautuvat suojelualueisiin. Selvää on, että luontokadon pysäyttämiseksi ja ei-puuntuotannollisten ekosysteemipalvelujen turvaamiseksi tarvitaan metsänkäsittelymenetelmien monipuolis-tamisen rinnalla merkittävästi lisäsuojelua.