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Sökning: hsv:(NATURVETENSKAP) hsv:(Geovetenskap och miljövetenskap) hsv:(Klimatforskning) > Klemedtsson Leif 1953

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1.
  • Vestin, Patrik, et al. (författare)
  • Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes
  • 2022
  • Ingår i: Iforest-Biogeosciences and Forestry. - : Italian Society of Sivilculture and Forest Ecology (SISEF). - 1971-7458. ; 15, s. 148-162
  • Tidskriftsartikel (refereegranskat)abstract
    • During 2010-2013, we investigated the effects of stump harvesting on greenide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224??103 and 1.442??103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070??103 and 1.696??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301??103 and 4.114??103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107??103 and 5.274??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.
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2.
  • Poyatos, R., et al. (författare)
  • Global transpiration data from sap flow measurements: the SAPFLUXNET database
  • 2021
  • Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:6, s. 2607-2649
  • Tidskriftsartikel (refereegranskat)abstract
    • Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.
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3.
  • He, Hongxing, 1987, et al. (författare)
  • Forests on drained agricultural peatland are potentially large sources of greenhouse gases – insights from a full rotation period simulation
  • 2015
  • Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; 12, s. 19673-19710
  • Tidskriftsartikel (refereegranskat)abstract
    • The CoupModel was used to simulate a Norway Spruce forest on fertile drained peat over 60 years, from planting in 1951 until 2011, describing abiotic, biotic and greenhouse gas (GHG) emissions (CO2 and N2O). By calibrating the model against tree ring data we obtained a "reference" model by which we were able to describe the fluxes and controlling factors over the 60 years. We discuss some conceptual issues relevant to improving the model in order to better understand peat soil simulations. However, the present model was able to describe the most important ecosystem dynamics such as the plant biomass development and GHG emissions. The GHG fluxes are composed of two important quantities, the forest carbon (C) uptake, 405 g C m−2 yr−1 and the decomposition of peat soil, 396 g C m−2 yr−1. N2O emissions contribute to the GHG emissions by 0.5 g N m−2 yr−1, corresponding to 56.8 g C m−2 yr−1. The 60-year-old Spruce forest has an accumulated biomass of 164 Mg C ha−1. However, over this period 208 Mg C ha−1 GHG has been added to the atmosphere, which means a net addition of GHG emissions. The main losses are from the peat soil and, indirectly, from forest thinning products, which we assume have a short lifetime. We conclude that after harvest at an age of 80 years, most of the stored biomass carbon is liable to be released, the system having captured C only temporarily and with a cost of disappeared peat, adding CO2 to the atmosphere.
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4.
  • Pavelka, M., et al. (författare)
  • Standardisation of chamber technique for CO2, N2O and CH4 fluxes measurements from terrestrial ecosystems
  • 2018
  • Ingår i: International Agrophysics. - : Walter de Gruyter GmbH. - 0236-8722 .- 2300-8725. ; 32:4, s. 569-587
  • Tidskriftsartikel (refereegranskat)abstract
    • Chamber measurements of trace gas fluxes between the land surface and the atmosphere have been conducted for almost a century. Different chamber techniques, including static and dynamic, have been used with varying degrees of success in estimating greenhouse gases (CO2, CH4, N2O) fluxes. However, all of these have certain disadvantages which have either prevented them from providing an adequate estimate of greenhouse gas exchange or restricted them to be used under limited conditions. Generally, chamber methods are relatively low in cost and simple to operate. In combination with the appropriate sample allocations, chamber methods are adaptable for a wide variety of studies from local to global spatial scales, and they are particularly well suited for in situ and laboratory-based studies. Consequently, chamber measurements will play an important role in the portfolio of the Pan-European long-term research infrastructure Integrated Carbon Observation System. The respective working group of the Integrated Carbon Observation System Ecosystem Monitoring Station Assembly has decided to ascertain standards and quality checks for automated and manual chamber systems instead of defining one or several standard systems provided by commercial manufacturers in order to define minimum requirements for chamber measurements. The defined requirements and recommendations related to chamber measurements are described here.
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5.
  • Hjerpe, Karin, et al. (författare)
  • Utsläpp av växthusgaser från torvmark
  • 2014
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Dikad torvmark i Sverige avgav sammanlagt drygt 11,4 miljoner ton koldioxidekvivalenter år 2012, enligt den senaste klimatrapporteringen. Denna mängd kan jämföras med de totala svenska utsläppen av växthusgaser, som beräknades uppgå till 57,6 miljoner ton koldioxidekvivalenter samma år. En åtgärd som skulle kunna minska utsläppen av växthusgaser från dikad torvmark är att återställa marken till våtmark, vilket minskar avgången av koldioxid och lustgas från marken. Samtidigt ökar avgången av metan, men minskningen av koldioxid- och lustgasutsläppen är större, vilket innebär att utsläppen av växthusgaser från marken totalt sett minskar. Om de ekonomiska resurserna för att återställa dikad torvmark till våtmark är begränsade bör man i första hand återställa dikade torvmarker som är stora källor för växthusgaser till våtmark. Studier av växthusgasutsläpp från dikade torvmarker som används för skogsproduktion visar att näringsrika och väldränerade marker är större källor för växthusgaser än näringsfattigare, fuktigare marker. Vi bedömer därför att det ur ett klimatperspektiv är viktigast att återställa dikad skogsmark med en kol:kväve-kvot under 25 som är frisk-fuktig eller torrare. Dikad torvmark som används för naturbete avger mindre växthusgaser än åkermark på dikad torvmark och därför är det viktigare att återställa åkermark till våtmark. Avgången av växthusgaser varierar mycket mellan olika åkrar på dikad torvmark. Det är dock inte möjligt att identifiera åkrar på dikad torvmark som är stora källor för växthusgaser utifrån markfuktighet eller kol:kväve-kvot, och inte heller utifrån några andra faktorer som är enkla att mäta. Detta beror sannolikt på att åkermarken generellt är så pass väldränerad och näringsrik att varken syreeller kvävetillgången är begränsande för avgången av koldioxid och lustgas. I ett längre tidsperspektiv kommer dikad torvmark att avge koldioxid och lustgas så länge det finns ett syresatt torvlager. Därför bedömer vi att det är viktigast att återställa dikad åkermark med tjockt torvlager till våtmark. Därtill bör mark som inte längre aktivt brukas prioriteras framför mark som fortfarande är i bruk. Utsläppen av växthusgaser verkar inte automatiskt minska när brukandet upphör och även om marken sannolikt kommer att försumpas på sikt, vilket innebär att utsläppen av växthusgaser minskar, kan det ta väldigt lång tid. Dessutom borde kostnaderna för att återställa marken till våtmark i genomsnitt bli lägre om marken inte längre används. Hur mycket avgången av växthusgaser minskar när dikad torvmark återställs till våtmark beror inte bara på hur stor avgången av växthusgaser från den dikade marken var utan också på hur stor avgången från den anlagda våtmarken blir. Utsläppen från våtmarken påverkas av hur den anläggs och sköts. För att våtmarken ska avge så lite växthusgaser som möjligt bör grundvattennivån höjas så mycket att förhållandena före dikningen återskapas. Om våtmarken anläggs på mark som använts för jordbruksproduktion bör dessutom vegetationen tas bort före återställandet. Anläggning av våtmarker kan också ge andra nyttor – våtmarkerna kan bland annat gynna biologisk mångfald och minska näringsläckaget till våra sjöar och vattendrag. När en våtmark ska anläggas och skötas behöver man ta hänsyn till alla dessa aspekter så att våtmarken ger så stor nytta som möjligt.
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6.
  • He, Hongxing, 1987, et al. (författare)
  • Factors controlling Nitrous Oxide emission from a spruce forest ecosystem on drained organic soil, derived using the CoupModel
  • 2016
  • Ingår i: Ecological Modelling. - : Elsevier. - 0304-3800 .- 1872-7026. ; 321, s. 46-63
  • Tidskriftsartikel (refereegranskat)abstract
    • High Nitrous Oxide (N2O) emissions have been identified in hemiboreal forests in association with draining organic soils. However, the specific controlling factors that regulate the emissions remain unclear. To examine the importance of different factors affecting N2O emissions in a spruce forest on drained organic soil, a process-based model, CoupModel, was calibrated using the generalized likelihood uncertainty estimation (GLUE) method. The calibration also aims to estimate parameter density distributions, the covariance matrix of estimated parameters and the correlation between parameters and variables information, useful when applying the model on other peat soil sites and for further model improvements. The calibrated model reproduced most of the high resolution data (total net radiation, soil temperature, groundwater level, net ecosystem exchange, etc.) very well, as well as cumulative measured N2O emissions (simulated 8.7±1.1kgN2Oha-1year-1 (n=97); measured 8.7±2.7kgN2Oha-1year-1 (n=6)), but did not capture every measured peak. Parameter uncertainties were reduced after calibration, in which 16 out of 20 parameters changed from uniform distributions into normal distributions or log normal distributions. Four parameters describing bypass water flow, oxygen diffusion and soil freezing changed significantly after calibration. Inter-connections and correlations between many calibrated parameters and variables reflect the complex and interrelated nature of pedosphere, biosphere and atmosphere interactions. This also highlights the need to calibrate a number of parameters simultaneously. Model sensitivity analysis indicated that N2O emissions during growing seasons are controlled by competition between plants and microbes for nitrogen, while during the winter season snow melt periods are important. Our results also indicate that N2O is mainly produced in the capillary fringe close to the groundwater table by denitrification in the anaerobic zone. We conclude that, in afforested drained peatlands, the plants and groundwater level have important influences on soil N availability, ultimately controlling N2O emissions.
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7.
  • Lembrechts, Jonas J., et al. (författare)
  • Global maps of soil temperature
  • 2022
  • Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
  • Tidskriftsartikel (refereegranskat)abstract
    • Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.
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8.
  • Junttila, Sofia, et al. (författare)
  • Upscaling Northern Peatland CO2 Fluxes Using Satellite Remote Sensing Data
  • 2021
  • Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 13:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Peatlands play an important role in the global carbon cycle as they contain a large soil carbon stock. However, current climate change could potentially shift peatlands from being carbon sinks to carbon sources. Remote sensing methods provide an opportunity to monitor carbon dioxide (CO2) exchange in peatland ecosystems at large scales under these changing conditions. In this study, we developed empirical models of the CO2 balance (net ecosystem exchange, NEE), gross primary production (GPP), and ecosystem respiration (ER) that could be used for upscaling CO2 fluxes with remotely sensed data. Two to three years of eddy covariance (EC) data from five peatlands in Sweden and Finland were compared to modelled NEE, GPP and ER based on vegetation indices from 10 m resolution Sentinel-2 MSI and land surface temperature from 1 km resolution MODIS data. To ensure a precise match between the EC data and the Sentinel-2 observations, a footprint model was applied to derive footprint-weighted daily means of the vegetation indices. Average model parameters for all sites were acquired with a leave-one-out-cross-validation procedure. Both the GPP and the ER models gave high agreement with the EC-derived fluxes (R-2 = 0.70 and 0.56, NRMSE = 14% and 15%, respectively). The performance of the NEE model was weaker (average R-2 = 0.36 and NRMSE = 13%). Our findings demonstrate that using optical and thermal satellite sensor data is a feasible method for upscaling the GPP and ER of northern boreal peatlands, although further studies are needed to investigate the sources of the unexplained spatial and temporal variation of the CO2 fluxes.
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9.
  • Öquist, Mats, et al. (författare)
  • The full annual carbon balance of boreal forestsis highly sensitive to precipitation
  • 2014
  • Ingår i: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 1:7, s. 315-319
  • Tidskriftsartikel (refereegranskat)abstract
    • The boreal forest carbon balance is predicted to be particularly sensitive to climate change. Carbon balance estimates of these biomes stem mainly from eddy-covariance measurements of net ecosystem exchange (NEE). However, a full net ecosystem carbon balance (NECB) must include the lateral carbon export (LCE) through discharge. We show that annual LCE at a boreal forest site ranged from 4 to 28%, averaging 11% (standard deviation of 8%), of annual NEE over 13 years. Annual LCE and NEE are strongly anticorrelated; years with weak NEE coincide with high LCE. The decreased NEE in response to increased precipitation is caused by a reduction in the amount of incoming radiation caused by clouds. If our finding is also valid for other sites, it implies that increased precipitation at high latitudes may shift forest NECB in large areas of the boreal biome. Our results call for future analysis of this dual effect of precipitation on NEE and LCE.
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10.
  • Schubert, Per, et al. (författare)
  • Modeling GPP in the Nordic forest landscape with MODIS time series data-Comparison with the MODIS GPP product
  • 2012
  • Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 126, s. 136-147
  • Tidskriftsartikel (refereegranskat)abstract
    • Satellite sensor-derived data are suitable for regional estimations of several important biophysical variables. Data with a finer spatial resolution should improve regional estimations of GPP (gross primary productivity), since they better capture the variation in a heterogeneous landscape. The main objective of this study was to investigate if MODIS 500 m reflectance data can be used to drive empirical models for regional estimations of GPP in Nordic forests. The performance of the proposed models was compared with the MODIS 1 km GPP product. Linear regression analyses were made on 8-day averages of eddy covariance GPP from three deciduous and ten coniferous sites in relation to MODIS 8-day composite data and 8-day averages of modeled incoming PPFD (photosynthetic photon flux density). Time series of EVI2 (two-band enhanced vegetation index) were calculated from MODIS 500 m reflectance data and smoothed by a curve fitting procedure. For most sites, GPP was fairly strongly to strongly related to the product of EVI2 and PPFD (Deciduous: R-2=0.45-0.86, Coniferous: R-2=0.49-0.90). Similar strengths were found between GPP and the product of EVI2 and MODIS 1 km daytime LST (land surface temperature) (R-2=0.55-0.81, 0.57-0.77) and between GPP and EVI2, PPFD and daytime LST in multiple linear regressions (R-2=0.73-0.89,0.65-0.93). One year of data was collected from all coniferous sites to derive a general empirical model for GPP versus (1) the product of EVI2 and PPFD (R-2=0.70), (2) the product of EVI2 and daytime LST (R-2=0.62) and (3) EVI2, PPFD and daytime LST (R-2=0.72). These three models were then validated at six sites for the remaining years by linearly relating eddy covariance GPP to modeled GPP, which resulted in fairly strong to strong relationships for most sites (R-2=0.49-0.91, RMSE=0.63-1.22 gC m(-2) day(-1), R-2=0.53-0.73, RMSE=0.90-1.43 gC m(-2) day(-1) R-2=0.56-0.87, RMSE=0.79-1.11 gC m(-2) day(-1)). In comparison, similar validation strengths were found for the latest collection 5.1 of the MODIS 1 km GPP product (R-2=0.59-0.88, RMSE=0.80-1.16 gC m(-2) day(-1)). The main conclusion is that the suggested empirical models driven by MODIS 500 m reflectance data can be used for regional estimations of Nordic forest GPP, while preserving a finer resolution than the MODIS 1 km GPP product. (C) 2012 Elsevier Inc. All rights reserved.
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