NDVI viimeaikaisen hiilen kertymän ja vihertymisen proksiaineistona Huippuvuorilla

Maailmanlaajuisissa vuosikeskilämpötiloissa on havaittu lämpenevä kehityssuuntaus esiteolliselta ajalta lähtien. Vuosikeskilämpötilojen muutos Norjan Huippuvuorilla on maailmanlaajuista keskiarvoa voimakkaampaa. Huippuvuorten läntisissä osissa jäätikköjen vetäytyminen on jatkunut jo useita vuosikymmeniä, ja viime vuosikymmeninä biologiset prosessit ovat kiihtyneet. Nämä muutokset ovat todennäköisesti vaikuttaneet Huippuvuorten pääosin sammalpeitteisten tundra-alueiden hiilidynamiikkaan. Alueella on toteutettu vain rajallinen määrä paleoekologisia tutkimuksia, eikä varsinkaan korkeiden leveysasteisten sammalpeitteisten tundra-alueiden vastetta ilmastonmuutokseen vielä täysin ymmärretä. Tämän tutkimuksen tavoitteena oli tutkia maaperän orgaanisen aineksen ja hiilen kertymisnopeuksien viimeaikaisia muutoksia sammalpeitteisillä tundra-alueilla Huippuvuorilla. Maaperän kairausprofiilit kerättiin neljältä koealalta Spitsbergen -saaren läntisistä osista. Radiohiili (14C) ja lyijyajoitusmenetelmiä (210Pb) käytettiin yhdessä ikä-syvyys -mallien ja maaperän ominaisuusanalyysien kanssa hiilen kertymishistorian rekonstruoimiseksi vuodesta 1900 jKr vuoteen 2018 jKr asti. Päätelmiä tukivat meteorologiset mittaukset alueelta. Lisäksi Landsat-satelliittiaineistosta johdettiin vuosittaisia normalisoituja kasvillisuusindeksejä vuodesta 1985 jKr vuoteen 2018 jKr, kasvillisuuden muutosten tutkimiseksi viime vuosikymmeninä. Kasvillisuusindeksien kykyä ennustaa maaperän hiilen kertymisen alueellista ja ajallista vaihtelua arvioitiin erikseen. Kehityssuuntaus pääasiallisesti mineraalipitoisista maaperistä orgaanisiksi maaperiksi havaittiin useissa näytteissä, tämä voi merkitä, että alueilla on käynnistynyt soistumisprosessi. Viimeaikaiset hiilen kertymisnopeudet kasvoivat jokaisella koealalla. Alueen meteorologinen aineisto yhdessä kirjallisuuden kanssa viittasi alueen abioottisten ja bioottisten ympäristötekijöiden yhdessä ilmasto- ja sääolosuhteiden kanssa ohjaavan kertymisprosesseja. Kasvillisuusindeksit osoittivat merkittäviä muutoksia kasvillisuuden rakenteessa ja tuottavuudessa. Viimeaikaisten hiilen kertymisnopeuksien ja kasvillisuusindeksien välisen suhteen arviointi, ei tuottanut luotettavia tuloksia. Maaperän ja ilmakehän välisten hiilivoiden alueellinen ja ajallinen heterogeenisyys tuottaa suuria haasteita tämänhetkisille mallintamismenetelmille. Maaperänäytteiden ja kaukokartoitusaineistojen yhteiskäyttöä tulisi edistää, jotta tulevia muutoksia kyettäisiin mallintamaan tarkemmin.A warming trend of annual average surface temperatures since pre-industrial times has been observed globally. High-arctic area of Svalbard, Norway is undergoing amplified change of annual average temperatures when compared to the global average. Decline of glaciers in western Svalbard has been ongoing for several decades, and in the recent past, rapid biological successions have taken place. These changes have likely had effect on regional scale carbon dynamics at Svalbard’s moss tundra areas. Possibly indicating onset of paludification process of these areas. However, palaeoecological studies from the area are scarce, and the response of high-latitude moss tundra areas to past or ongoing climate change, are still not fully understood. This thesis aimed to bring forward information of changes in recent organic matter and carbon accumulation rates at Svalbard, Norway. Soil profiles were collected from four moss tundra sites, located on coastal areas and fjords descending towards Isfjorden, on the western side of Spitsbergen island. Radiocarbon (14C) and lead (210Pb) dating methods with novel age-depth modelling and soil property analyses, were used to reconstruct recent organic matter and carbon accumulation histories from 1900 AD to 2018 AD. Accumulation histories were supported by meteorological measurements from the area. In addition, annual maximum value Normalized Difference Vegetation Indices for 1985 AD till 2018 AD period were produced, to study vegetation succession in the recent past. Lastly, possibility to predict spatiotemporal variation of soil carbon accumulation with satellite derived vegetation indices was assessed. Development from predominantly mineral soils to organic soils was distinguishable within multiple soil profiles, pointing to potential paludification. Recent apparent carbon accumulation rates showed an increasing trend. Supporting meteorological data and literature suggest that regional abiotic and biotic factors in synergy with weather and climate are contributing to this observed trend. Vegetation indices pointed to major changes in vegetation composition and productivity. However, investigation of relationship between recent carbon accumulation rates and vegetation indices did not produce reliable results. Spatiotemporal heterogeneity of carbon soil-atmosphere fluxes presently imposes large challenges for such modelling. To alleviate this problem, efforts for more efficient synergetic use of field sampling and remote sensing -based material should be undertaken, to improve modelling results

Newly initiated carbon stock, organic soil accumulation patterns and main driving factors in the High Arctic Svalbard, Norway

High latitude organic soils form a significant carbon storage and deposition of these soils is largely driven by climate. Svalbard, Norway, has experienced millennial-scale climate variations and in general organic soil processes have benefitted from warm and humid climate phases while cool late Holocene has been unfavourable. In addition to direct effect of cool climate, the advancing glaciers have restricted the vegetation growth, thus soil accumulation. Since the early 1900’s climate has been warming at unprecedented rate, assumingly promoting organic soil establishment. Here we present results of multiple organic soil profiles collected from Svalbard. The profiles have robust chronologies accompanied by soil property analyses, carbon stock estimations and testate amoeba data as a proxy for soil moisture. Our results reveal relatively recent initiation of organic soils across the Isfjorden area. The initiation processes could be linked to glacier retreat, and improvement of growing conditions and soil stabilization. Carbon stock analyses suggested that our sites are hot spots for organic matter accumulation. Testate amoebae data suggested drying of soil surfaces, but the reason remained unresolved. If continued, such a process may lead to carbon release. Our data suggest that detailed palaeoecological data from the Arctic is needed to depict the on-going processes and to estimate future trajectories.Peer reviewe

Features predisposing forest to bark beetle outbreaks and their dynamics during drought

Climate change is estimated to increase the risk of the bark beetle (Ips typographus L.) mass outbreaks in Norway Spruce (Picea abies (L.) Karst) forests. Habitats that are thermally suitable for bark beetles may expand, and an increase in the frequency and intensity of droughts can promote drought stress on host trees. Drought affects tree vigor and in unison with environmental features it influences the local predisposition risk of forest stands to bark beetle attacks. We aimed to study how various environmental features influence the risk of bark beetle attacks during a drought year and the following years with more normal weather conditions but with higher bark beetle populations. We included features representing local forest stand attributes, topography, soil type and wetness, the proximity of clear-cuts and previous bark beetle attacks, and a machine learning algorithm (random forest) was applied to study the variation of predisposition risk across a 48,600 km2 study area in SE Sweden.Forest stands with increased risk of bark beetle attack were distinguished with high accuracy both during drought and in normal weather conditions. The results show that during both study periods, spruce and mixed coniferous forests had elevated risk of attack, while forests with a mix of deciduous and coniferous trees had a lower risk. Forests with high average canopy height were strongly predisposed to bark beetle attacks. However, during the drought year risk was more similar between stands with lower and higher canopy height, suggesting that during drought periods younger trees can be predisposed to bark beetle attacks. The importance of soil moisture and position within the local landscape were highlighted as important features during the drought year.Identifying areas with increased risk, supported by information on how environmental features control the predisposition risk during drought, could aid adaptation strategies and forest management intervention efforts. We conclude that geospatial data and machine learning have the potential to further support the digitalization of the forest industry, facilitating development of methods capable to quantify importance and dynamics of environmental features controlling the risk in local context. Corresponding methods could help to direct management actions more effectively and offer information for decision-making in changing climate

Soil GHG dynamics after water level rise – Impacts of selection harvesting in peatland forests

Managed boreal peatlands are widespread and economically important, but they are a large source of greenhouse gases (GHGs). Peatland GHG emissions are related to soil water-table level (WT), which controls the vertical distribution of aerobic and anaerobic processes and, consequently, sinks and sources of GHGs in soils. On forested peatlands, selection harvesting reduces stand evapotranspiration and it has been suggested that the resulting WT rise decreases soil net emissions, while the tree growth is maintained. We monitored soil concentrations of CO2, CH4, N2O and O2 by depth down to 80 cm, and CO2 and CH4 fluxes from soil in two nutrient-rich Norway spruce dominated peatlands in Southern Finland to examine the responses of soil GHG dynamics to WT rise. Selection harvesting raised WT by 14 cm on both sites, on average, mean WTs of the monitoring period being 73 cm for unharvested control and 59 cm for selection harvest. All soil gas concentrations were associated with proximity to WT. Both CH4 and CO2 showed remarkable vertical concentration gradients, with high values in the deepest layer, likely due to slow gas transfer in wet peat. CH4 was efficiently consumed in peat layers near and above WT where it reached sub-atmospheric concentrations, indicating sustained oxidation of CH4 from both atmospheric and deeper soil origins also after harvesting. Based on soil gas concentration data, surface peat (top 25/30 cm layer) contributed most to the soil-atmosphere CO2 fluxes and harvesting slightly increased the CO2 source in deeper soil (below 45/50 cm), which could explain the small CO2 flux differences between treatments. N2O production occurred above WT, and it was unaffected by harvesting. Overall, the WT rise obtained with selection harvesting was not sufficient to reduce soil GHG emissions, but additional hydrological regulation would have been needed.Peer reviewe

Reasons to be cheerful? Reflections on GPs' responses to depression

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes