Carbon dynamics in forest fire affected permafrost soils

Northern Hemisphere permafrost soils store approximately 50% of the global soil carbon (C), a quarter of which could thaw by the end of the century. Thawing exposes previously frozen soil organic matter (SOM) to decomposition, resulting in release of greenhouse gases (GHG) from the soils. Vast areas of permafrost soils are covered by boreal forests currently acting as sinks of C. As global warming is strongest at northern latitudes, the occurrence of boreal forest fires may increase. Forest fires further advance permafrost thaw and forest soils may turn from sinks to sources. This thesis examines how forest fires affect the quality of SOM and GHG emissions from permafrost soils in boreal forests by conducting chemical fractionation of SOM and soil incubations, as well as manual chamber measurements of GHGs. Forest fires increased the active layer depth on top of permafrost, altered species composition of vegetation and affected the organic layer depth and the SOM pools. Fires decreased the quality of SOM, observed as reduction in the proportional amount of labile SOM fraction and increased SOM temperature sensitivity, as well as enrichment with heavier isotopes of 13C and 15N. GHG measurements showed that fire initially decreased carbon dioxide flux from the soil and it returned to its pre-fire status approximately 50 years after the fire. The effects of fires on methane and nitrous oxide fluxes were not significant. Forest fires have significant effects on the release of GHGs from permafrost soils. In the future, the fate of permafrost stored SOM is dependent on its degradability, the frequency of fire events and the ability of forests to regenerate, allowing permafrost recovery, in the changing climate. There is a demand for further studies investigating the specifics of different permafrost ecosystems and building a complete picture to estimate total emissions from permafrost regions.Pohjoisen pallonpuoliskon ikiroudan alueet varastoivat noin 50 % maapallon maaperän hiilivaroista. Noin neljänneksen ikiroudasta on ennustettu sulavan vuosisadan loppuun mennessä ja sulaminen altistaa jäätyneet hiilivarat hajoamiselle, jolloin nämä varastot muuttuvat hiilen nieluista kasvihuonekaasulähteiksi. Suuri osa ikiroudan alueesta sijaitsee boreaalisella metsävyöhykkeellä, joka tällä hetkellä toimii merkittävänä hiilinieluna. Ilmastonmuutoksen myötä metsäpalot voivat kuitenkin yleistyä. Metsäpalot edesauttavat ikiroudan sulamista, jolloin nämä metsämaat muuttuvat hiilinieluista lähteiksi. Tässä väitöskirjassa tutkitaan, kuinka metsäpalot vaikuttavat maan orgaanisen aineksen laatuun ja kasvihuonekaasupäästöihin ikiroudan alueella. Tutkimustapoina on käytetty orgaanisen aineksen kemiallista fraktiointia, maainkubointeja ja kasvihuonekaasujen manuaalisia kammiomittauksia. Tutkimuksissa havaittiin, että metsäpalot kasvattivat aktiivisen kerroksen (kausittaisesti sulava ja jäätyvä kerros) paksuutta ikiroudan päällä, muuttivat kasvillisuussuhteita, maan orgaanisen aineksen paksuutta ja hiilivarastoja. Palot huononsivat maan orgaanisen aineksen laatua, joka ilmeni helppoliukoisen orgaanisen aineksen suhteellisena vähentymisenä, ja nostivat orgaanisen aineksen lämpötilaherkkyyttä. Myös raskaampien isotooppien (13C ja 15N) suhteellinen osuus oli suurempi palon jälkeen. Kammiomittaukset osoittivat, että palo aluksi pienensi hiilidioksidipäästöjä ja nämä päästöt palasivat alkuperäiselle tasolleen noin 50 vuotta palon jälkeen. Sen sijaan metsäpaloilla ei ollut merkittävää vaikutusta metaani- ja dityppimonoksidivoihin. Metsäpalot vaikuttavat kasvihuonekaasujen vapautumiseen ikiroudan maista. Tulevaisuudessa ikiroudan varastoiman orgaanisen aineksen kohtalo on riippuvainen sen hajoamisherkkyydestä, metsäpalojen esiintyvyydestä ja metsien uudistumiskyvystä, joka mahdollistaa ikiroudan uusiutumisen muuttuvassa ilmastossa. Kokonaisvaltaisen käsityksen muodostaminen ikiroudan ekosysteemien tulevista päästöistä vaatii lisätutkimuksia, jotka ottavat huomioon kunkin ekosysteemin erityispiirteet

Valoisa vanhuus : sosiokulttuurista innostamista taidelähtöisten menetelmien avulla Betel-kodissa

Tämän opinnäytetyön tarkoituksena ja tavoitteena oli yrittää parantaa Betel-kodin ikäihmisten osallisuutta ja elämänhallintaa sekä vahvistaa yhteisöllisyyttä. Tavoitteena oli parantaa myös asiakkaan ja henkilökunnan välistä suhdetta. Tietoperustana opinnäytetyössä on sosiaalipedagogiikka, sosiokulttuurinen innos-taminen ja elämänkaariteoria. Sosiokulttuurinen innostaminen tuo malleja vanhus-työn kehittämiseen. Innostamisessa on aina mukana pedagoginen, sosiaalinen ja kulttuurinen ulottuvuus. Toteutimme toiminnallisen opinnäytetyön ryhmätoimintana, jossa käytimme taide-lähtöisiä menetelmiä, muistelutyötä, valokuvatyöskentelyä ja maalausta. Kävimme ryhmässä läpi taidelähtöisten menetelmien avulla kuuden ikäihmisen elämäntarinan lapsuudesta vanhuuteen. Prosessin aikana ryhmään osallistuneiden ikäihmisten osallisuus ja elämänhallinta paranivat. Ryhmään osallistuvilla oli mahdollisuus kuunnella ja tulla kuulluksi. Vertaistuen kautta yhteisöllisyys vahvistui. Taidelähtöiset menetelmät tukivat pro-sessin tuloksia. Ikäihmiset tarvitsevat tämän opinnäytetyön kaltaista työskentelyä oman identiteet-tinsä vahvistamiseksi. Opinnäytetyössä kuvattu sosiokulttuurinen innostaminen on toimiva ja voimauttava työote ikäihmisten parissa.The project was centred on a group of elderly residents of Betel-home, and had the aim of stimulating both social participation and individual autonomy and strength-ening the sense of communality within the home. There was the additional goal of facilitating an improvement in the relationships between residents and members of staff. The foundations of this thesis derive from the findings of social pedagogy, so-ciocultural motivation and the use of the life story. Sociocultural motivation pro-vides models for the development of work with the aged. Motivation always con-tains elements of a pedagogic, social and cultural dimension. The project was conducted in a group setting, and consisted of art-based methods, reminiscing, painting and work with photographs. The whole process documented the biographies of six elderly participants, from childhood to old age. As the study progressed the level of social participation and autonomy displayed by the elderly participants increased. They had the opportunity of both listening and of being heard. The sense of communality was enhanced through the use of comparative methods. The use of art-based methods supported the outcome of the process. Older people need the kind of collaborative work employed in this project, in or-der to strengthen their identities. Sociocultural motivation, as here described, is an effective and empowering tool in work with the aged

How do forest fires affect soil greenhouse gas emissions in upland boreal forests? A review

Wildfires strongly regulate carbon (C) cycling and storage in boreal forests and account for almost 10% of global fire C emissions. However, the anticipated effects of climate change on fire regimes may destabilize current C-climate feedbacks and switch the systems to new stability domains. Since most of these forests are located in upland soils where permafrost is widespread, the expected climate warming and drying combined with more active fires may alter the greenhouse gas (GHG) budgets of boreal forests and trigger unprecedented changes in the global C balance. Therefore, a better understanding of the effects of fires on the various spatial and temporal patterns of GHG fluxes of different physical environments (permafrost and nonpermafrost soils) is fundamental to an understanding of the role played by fire in future climate feedbacks. While large amounts of C are released during fires, postfire GHG fluxes play an important role in boreal C budgets over the short and long term. The timescale over which the vegetation cover regenerates seems to drive the recovery of C emissions after both low- and high-severity fires, regardless of fire-induced changes in soil decomposition. In soils underlain by permafrost, fires increase the active layer depth for several years, which may alter the soil dynamics regulating soil GHG exchange. In a scenario of global warming, prolonged exposition of previously immobilized C could result in higher carbon dioxide emission during the early fire succession. However, without knowledge of the contribution of each respiration component combined with assessment of the warming and drying effects on both labile and recalcitrant soil organic matter throughout the soil profile, we cannot advance on the most relevant feedbacks involving fire and permafrost. Fires seem to have either negligible effects on methane (CH4) fluxes or a slight increase in CH4 uptake. However, permafrost thawing driven by climate or fire could turn upland boreal soils into temporary CH4 sources, depending on how fast the transition from moist to drier soils occurs. Most studies indicate a slight decrease or no significant change in postfire nitrous oxide (N2O) fluxes. However, simulations have shown that the temperature sensitivity of denitrification exceeds that of soil respiration; thus, the effects of warming on soil N2O emissions may be greater than on C emissions.Peer reviewe

Soil organic matter decomposition and temperature sensitivity after forest fire in permafrost regions in Canada

Non peer reviewe

Comparing an exponential respiration model to alternative models for soil respiration components in a Canadian wildfire chronosequence (FireResp v1.0)

Forest fires modify soil organic carbon and suppress soil respiration for many decades after the initial disturbance. The associated changes in soil autotrophic and heterotrophic respiration from the time of the forest fire, however, are less well characterized. The FireResp model predicts soil autotrophic and heterotrophic respiration parameterized with a novel dataset across a fire chronosequence in the Yukon and Northwest Territories of Canada. The dataset consisted of soil incubation experiments and field measurements of soil respiration and soil carbon stocks. The FireResp model contains submodels that consider a Q(10) (exponential) model of respiration compared to models of heterotrophic respiration using Michaelis-Menten kinetics parameterized with soil microbial carbon. For model evaluation we applied the Akaike information criterion and compared predicted patterns in components of soil respiration across the chronosequence. Parameters estimated with data from the 5 cm soil depth had better model-data comparisons than parameters estimated with data from the 10 cm soil depth. The model-data fit was improved by including parameters estimated from soil incubation experiments. Models that incorporated microbial carbon with Michaelis-Menten kinetics reproduced patterns in autotrophic and heterotrophic soil respiration components across the chronosequence. Autotrophic respiration was associated with aboveground tree biomass at more recently burned sites, but this association was less robust at older sites in the chronosequence. Our results provide support for more structured soil respiration models than standard Q(10) exponential models.Peer reviewe

Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada

Forest fires are one of the most important natural disturbances in boreal forests, and their occurrence and severity are expected to increase as a result of climate warming. A combination of factors induced by fire leads to a thawing of the near-surface permafrost layer in subarctic boreal forest. Earlier studies reported that an increase in the active layer thickness results in higher carbon dioxide (CO2) and methane (CH4) emissions. We studied changes in CO2, CH4 and nitrous oxide (N2O) fluxes in this study, and the significance of several environmental factors that influence the greenhouse gas (GHG) fluxes at three forest sites that last had fires in 2012, 1990 and 1969, and we compared these to a control area that had no fire for at least 100 years. The soils in our study acted as sources of CO2 and N2O and sinks for CH4. The elapsed time since the last forest fire was the only factor that significantly influenced all studied GHG fluxes. Soil temperature affected the uptake of CH4, and the N2O fluxes were significantly influenced by nitrogen and carbon content of the soil, and by the active layer depth. Results of our study confirm that the impacts of a forest fire on GHGs last for a rather long period of time in boreal forests, and are influenced by the fire induced changes in the ecosystem. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Boreal forest soil is a significant and diverse source of volatile organic compounds

Vegetation emissions of volatile organic compounds (VOCs) are intensively studied world-wide, because oxidation products of VOCs contribute to atmospheric processes. The overall aim of this study was to identify and quantify the VOCs that originate from boreal podzolized forest soil at different depths, in addition to studying the association of VOC concentrations with VOC and CO2 fluxes from the boreal forest floor.Peer reviewe

Gradients and dynamics of inner bark and needle osmotic potentials in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst)

Preconditions of phloem transport in conifers are relatively unknown. We studied the variation of needle and inner bark axial osmotic gradients and xylem water potential in Scots pine and Norway spruce by measuring needle and inner bark osmolality in saplings and mature trees over several periods within a growing season. The needle and inner bark osmolality was strongly related to xylem water potential in all studied trees. Sugar concentrations were measured in Scots pine, and they had similar dynamics to inner bark osmolality. The sucrose quantity remained fairly constant over time and position, whereas the other sugars exhibited a larger change with time and position. A small osmotic gradient existed from branch to stem base under pre-dawn conditions, and the osmotic gradient between upper stem and stem base was close to zero. The turgor in branches was significantly driven by xylem water potential, and the turgor loss point in branches was relatively close to daily minimum needle water potentials typically reported for Scots pine. Our results imply that xylem water potential considerably impacts the turgor pressure gradient driving phloem transport and that gravitation has a relatively large role in phloem transport in the stems of mature Scots pine trees.Peer reviewe

Temperature sensitivity of soil organic matter decomposition after forest fire in Canadian permafrost region

Climate warming in arctic/subarctic ecosystems will result in increased frequency of forest fires, elevated soil temperatures and thawing of permafrost, which have implications for soil organic matter (SOM) decomposition rates, the CO2 emissions and globally significant soil C stocks in this region. It is still unclear how decomposability and temperature sensitivity of SOM varies in different depths and different stages of succession following forest fire in permafrost regions and studies on long term effects of forest fires in these areas are lacking. To study this question, we took soil samples from 5, 10 and 30 cm depths from forest stands in Northwest Canada, underlain by permafrost, that were burnt by wildfire 3, 25 and over 100 years ago. We measured heterotrophic soil respiration at 1, 7, 13 and 19 °C. Fire had a significant effect on the active layer depth, and it increased the temperature sensitivity (Q10) of respiration in the surface (5 cm) and in the deepest soil layer (30 cm) in the 3-year-old area compared to the 25- and more than 100-year-old areas. Also the metabolic quotient (qCO2) of soil microbes was increased after fire. Though fires may facilitate the SOM decomposition by increasing active layer depth, they also decreased SOM quality, which may limit the rate of decomposition. After fire all of these changes reverted back to original levels with forest succession.Peer reviewe

Changes in fluxes of carbon dioxide and methane caused by fire in Siberian boreal forest with continuous permafrost

Rising air temperatures and changes in precipitation patterns in boreal ecosystems are changing the fire occurrence regimes (intervals, severity, intensity, etc.). The main impacts of fires are reported to be changes in soil physical and chemical characteristics, vegetation stress, degradation of permafrost, and increased depth of the active layer. Changes in these characteristics influence the dynamics of carbon dioxide (CO2) and methane (CH4) fluxes. We have studied the changes in CO2 and CH4 fluxes from the soil in boreal forest areas in central Siberia underlain by continuous permafrost and the possible impacts of the aforementioned environmental factors on the emissions of these greenhouse gases. We have used a fire chronosequence of areas, with the last fire occurring 1, 23, 56, and more than 100 years ago. The soils in our study acted as a source of CO2. Emissions of CO2 were lowest at the most recently burned area and increased with forest age throughout the fire chronosequence. The CO2 flux was influenced by the pH of the top 5cm of the soil, the biomass of the birch (Betula) and alder (Duschekia) trees, and by the biomass of vascular plants in the ground vegetation. Soils were found to be a CH4 sink in all our study areas. The uptake of CH4 was highest in the most recently burned area (forest fire one year ago) and the lowest in the area burned 56 years ago, but the difference between fire chronosequence areas was not significant. According to the linear mixed effect model, none of the tested factors explained the CH4 flux. The results confirm that the impact of a forest fire on CO2 flux is long-lasting in Siberian boreal forests, continuing for more than 50 years, but the impact of forest fire on CH4 flux is minimal.Peer reviewe