| 1. |
- Evans, Christopher, et al.
(author)
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The impact of wildfire on biogeochemical fluxes and water quality in boreal catchments
- 2021
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 18, s. 3243-3261
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Journal article (peer-reviewed)abstract
- Wildfires are the major disturbance in boreal ecosystems and are of great importance for the biogeochemical cycles of carbon (C) and nutrients. However, these fire-induced impacts are hard to quantify and are rarely assessed together at an ecosystem level incorporating both aquatic and terrestrial environments. Following a wildfire in Sweden in an area with ongoing monitoring, we conducted a pre-fire (9 years) and post-fire (4 years) multi-catchment investigation of element losses (combustion and leaching) and impacts on water quality. Direct C and nitrogen (N) losses through combustion were ca. 4500 and 100 gm(-2), respectively. Net CO2 loss associated with soil and biomass respiration was similar to 150 g C m(-2) during the first year, but the ecosystem started to show net CO2 uptake in June 3 years post-fire. Aquatic C and N losses the first 12 months post-fire were 7 and 0.6 gm(-2), respectively. Hence, soil respiration comprised a non-negligible part of the post-fire C loss, whereas aquatic C losses were minor and did not increase post-fire. However, other elements (e.g. Ca, S) exhibited ecologically relevant increases in fluvial export and concentration with large peaks in the immediate post-fire period. The temporal dynamics of stream concentrations (Ca2+, Mg2+, K+,SO4-2, Cl-, NH4+, total organic N) suggest the presence of faster- and slower-release nutrient pools with half-lives of around 2 weeks and 4 months which we attribute to physicochemically and biologically mediated mobilization processes, respectively. Three years after the fire, it appears that dissolved fluxes of nutrients have largely returned to pre-fire conditions, but there is still net release of CO2.
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| 2. |
- Franz, D, et al.
(author)
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Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe´s terrestrial ecosystems: a review
- 2018
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In: International Agrophysics. - : Walter de Gruyter GmbH. - 0236-8722 .- 2300-8725. ; 32, s. 439-455
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Journal article (peer-reviewed)abstract
- Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.
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| 3. |
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| 4. |
- Grelle, Achim, et al.
(author)
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Affordable relaxed eddy accumulation system to measure fluxes of H2O, CO2, CH4 and N2O from ecosystems
- 2021
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 307
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Journal article (peer-reviewed)abstract
- The relaxed eddy accumulation (REA) technique is frequently applied to measure fluxes of a large variety of atmospheric tracers above ecosystems. It is often the method of choice since the eddy covariance (EC) technique is limited to a few tracers due to the lack of fast response analysers, high financial costs and in some cases high power consumption. REA avoids the need for a fast response analyser by collecting air from up-drafts and down-drafts into separate reservoirs. After collecting the air over a predefined time period, trace gas concentrations in the reservoirs are analysed by a slow response analyser and the average fluxes can be calculated.We developed and tested a REA system that is capable of measuring CO2, CH4, N2O and H2O fluxes simultaneously with only one gas analyser (Picarro G2805). This system is compatible with virtually any gas analyser and thus supports the flux analysis of a wide range of other air constituents such as isotopes, aerosols and volatile organic compounds. Furthermore, the modular design and rugged casing makes the sampling system robust and portable, and with its 12 V DC operation it is suitable for a wide range of field campaigns. The performance of the REA system was tested during the growing seasons of 2018 and 2020 on a grassland on organic soil in central Sweden.The system has worked reliably during several months in the Nordic climate, covering ambient temperatures between -20°C and +30°C. Measured fluxes of CO2 and H2O agree well with fluxes measured independently by an EC system. The similarity in the technology and the determined detection limits made us confident that the REA system even captures fluxes of CH4 and N2O well.
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| 5. |
- Grelle, Achim, et al.
(author)
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Carbon balance of a forest ecosystem after stump harvest
- 2012
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 27, s. 762-773
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Journal article (peer-reviewed)abstract
- Stump harvest in forests can cause both reductions of CO2 emissions through a decrease of decomposable substrate (direct effect) and emission increases as a consequence of deep and extensive soil disturbance (indirect effect). Here, the effects of stump harvest on net ecosystem CO2 exchange (NEE) in a former Norway spruce stand in mid Sweden are presented. CO2 exchange was continuously followed by eddy-covariance measurements during the first years after harvest. Differences in NEE from stump harvested and mounded (reference) plots were determined by soil-surface respiration measurements. Respiration from decaying stumps was estimated by a decomposition model. Fluxes indicated a direct effect (decreased efflux) during the first year after harvest that corresponded to the absence of decomposing stumps. During the following years, this emission reduction was increasingly counteracted by an indirect effect (increased efflux) of similar magnitude. This means that the expected emissions caused by extra soil disturbance occur with a certain delay and seem to increase with time. By these emissions, the substitution efficiency of stumps as bioenergy resource is reduced. Furthermore, at a time scale of centuries, instant combustion of stumps leads to a larger contribution to global warming than slow decomposition, because the stump carbon is available earlier in form of greenhouse gas. This is estimated by the time integral of emissions. Thus, despite the surprisingly low initial emissions, the overall substitution efficiency and climate benefits of stump harvest are likely to be small. The long-term consequences of stump harvest for the carbon budget are, however, still uncertain.
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| 6. |
- Grelle, Achim
(author)
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Environmental Aspects of Willow Cultivation for Bioenergy
- 2015
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In: Sustainable Biofuels: an Ecological Assessment of the Future Energy. - : DE GRUYTER. - 9783110275896 ; , s. 119-134
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Book chapter (peer-reviewed)abstract
- Aims and ScopeWith oil resources approaching their limits, biofuels have become increasingly attractive. This book provides a detailed description of the ecological implications of second and third generation biofuel feedstock production systems, beginning with an introduction to the importance of ecological sustainability alongside economic viability. The book is divided into sections describing theoretical foundation and benefits of various biofuel cropping systems, and providing a description of practical ecological limitations to achieve those fundamental benefits. The book covers such critical issues as greenhouse gas emissions, carbon balance, water cycle components, other biogeochemical and socioeconomic interactions alongside life cycle analysis principals for achieving sustainability. These are some of the most important sustainability, environmental and economic issues which biofuel industry and scientific community is seeking answers to.
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| 7. |
- Grelle, Achim
(author)
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ForestTemp - Sub-canopy microclimate temperatures of European forests
- 2021
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27, s. 6307-6319
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Journal article (peer-reviewed)abstract
- Ecological research heavily relies on coarse-gridded climate data based on standardized temperature measurements recorded at 2 m height in open landscapes. However, many organisms experience environmental conditions that differ substantially from those captured by these macroclimatic (i.e. free air) temperature grids. In forests, the tree canopy functions as a thermal insulator and buffers sub-canopy microclimatic conditions, thereby affecting biological and ecological processes. To improve the assessment of climatic conditions and climate-change-related impacts on forest-floor biodiversity and functioning, high-resolution temperature grids reflecting forest microclimates are thus urgently needed. Combining more than 1200 time series of in situ near-surface forest temperature with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub-canopy temperature at 15 cm above the surface and free-air temperature over the period 2000-2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories. We found that sub-canopy air temperatures differ substantially from free-air temperatures, being on average 2.1 degrees C (standard deviation +/- 1.6 degrees C) lower in summer and 2.0 degrees C higher (+/- 0.7 degrees C) in winter across Europe. Additionally, our high-resolution maps expose considerable microclimatic variation within landscapes, not captured by the gridded macroclimatic products. The provided forest sub-canopy temperature maps will enable future research to model below-canopy biological processes and patterns, as well as species distributions more accurately.
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| 8. |
- Grelle, Achim, et al.
(author)
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From source to sink : recovery of the carbon balance in young forests
- 2023
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In: Agricultural and Forest Meteorology. - : Elsevier. - 0168-1923 .- 1873-2240. ; 330
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Journal article (peer-reviewed)abstract
- We analyzed ecosystem carbon fluxes from eddy-covariance measurements in five young forests in southernSweden where the previous stand had been harvested by clear-cutting or wind-felled: three stands with Norwayspruce (Picea abies (L.) Karst.), one with Scots pine (Pinus sylvestris) and one with Larch (Larix x eurolepis A.Henry). One of the spruce stands had the stumps harvested, one was fertilized and one without any specialtreatments. These stands returned from positive (sources) to negative (sinks) annual carbon fluxes 8–13 yearsafter disturbance, depending on site productivity and management. This corresponds to approximately 15% ofthe rotation periods at these sites. Extrapolation in combination with chronosequence data suggests thatconventionally regenerated stands reach a neutral carbon balance after approximately 30% of the rotationperiod. The lowest carbon emissions and shortest recovery time was observed in a stand where the stumps of thetrees, in addition to the stems and logging residues, were removed after harvest. This stand not only returned to acarbon sink within this time period but the total carbon gains since disturbance also equaled the total losses afteronly 11 years. These results stress that production stands in southern Sweden are carbon sources during arelatively small part of the rotation period, and that this part can be considerably shortened by measures thatincrease productivity or reduce the amount of woody debris left after disturbance.
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| 9. |
- Grelle, Achim
(author)
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Improved trace gas flux estimation through IRGA sampling optimization
- 2009
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 149, s. 623 – 638-
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Journal article (peer-reviewed)abstract
- We examine the theoretical and practical aspects of improving the sampling methods of spectroscopic trace gas sensors of Eddy covariance flux measurement systems. Theory is developed based on non-ideal ventilation devices and existing equations for tube flow and attenuation of non-reactive trace gases and temperature. Model results indicate an optimum design exists which can be expressed in relation to intake tube diameter and which depends upon the ventilation device employed. Field experiment results (employing modified open path IRGAs) show that the use of short intake tubes can reduce flux losses by trace gas signal attenuation while minimizing the adjustments required for density fluctuations, with additional benefits of increased data capture under adverse environmental conditions. (C) 2008 Elsevier B.V. All rights reserved.
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| 10. |
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| 11. |
- Grelle, Achim
(author)
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Vegetation-specific model parameters are not required for estimating gross primary production
- 2014
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In: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 292, s. 1-10
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Journal article (peer-reviewed)abstract
- Models of gross primary production (GPP) based on remote sensing measurements are currently parameterized with vegetation-specific parameter sets and therefore require accurate information on the distribution of vegetation to drive them. Can this parameterization scheme be replaced with a vegetation-invariant set of parameters that can maintain or increase model applicability by reducing errors introduced from the uncertainty of land cover classification? Based on the measurements of ecosystem carbon fluxes from 168 globally distributed sites in a range of vegetation types, we examined the predictive capacity of seven light use efficiency (LUE) models. Two model experiments were conducted: (i) a constant set of parameters for various vegetation types and (ii) vegetation-specific parameters. The results showed no significant differences in model performance in simulating GPP while using both set of parameters. These results indicate that a universal of set of parameters, which is independent of vegetation cover type and characteristics can be adopted in prevalent LUE models. Availability of this well tested and universal set of parameters would help to improve the accuracy and applicability of LUE models in various biomes and geographic regions. (C) 2014 Elsevier B.V. All rights reserved.
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| 12. |
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| 13. |
- Gustafsson, Lena, et al.
(author)
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Rapid ecological response and intensified knowledge accumulation following a north European mega-fire
- 2019
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 34:4, s. 234-253
-
Research review (peer-reviewed)abstract
- Deepened knowledge on response of biota and ecological processes following fire is essential for a future with warmer climate and more disturbances. In 2014 the first mega-fire (13,100 ha) for at least a century in Scandinavia hit south-central Sweden, in a production forest landscape shaped by clearcutting forestry. Ecological dynamics is followed in >20 projects from universities, authorities and citizen science initiatives, rapidly accumulating substantial amounts of data. We outline projects and summarize their results during the first four years, demonstrating a rapid succession of fungi, lichens, vascular plants, birds, mammals, ticks, butterflies, beetles, and drastically altered carbon dynamics. We characterize forest operations including regeneration measures and point to patterns in pest and pathogen infestations. 8,000 ha is set aside for natural succession, with the rest harvested and managed for forest production, offering excellent opportunities for studies on salvage logging effects, already evident for birds. We demonstrate a strong regrowth of deciduous trees, and the protected part will in some decades likely develop into the largest deciduous-dominated area in boreal north Europe outside Russia. Continued studies of biodiversity and ecological processes are urgent for this unique area.
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| 14. |
- Hadden, David, et al.
(author)
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Changing temperature response of respiration turns boreal forest from carbon sink into carbon source
- 2016
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 223, s. 30-38
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Journal article (peer-reviewed)abstract
- Seventeen years (1997-2013) of carbon dioxide (CO2) fluxes were measured in a boreal forest stand in northern Sweden using the eddy covariance technique. During the measurement period the forest turned from a net carbon sink into a net carbon source. The net ecosystem exchange (NEE) was separated using values from periods of darkness into the gross components of total ecosystem respiration (TER) and gross primary productivity (GPP), which was calculated as GPP=-NEE + TER. From the gross components we could determine that an increase in TER during the autumn (September to end of November) and spring (March to end of May) periods resulted in the forest becoming a net source of CO2, We observed no increase in the GPP from the eddy covariance measurements. This was further supported by measurements of tree growth rings. The increased TER was attributed to a change in the forest's temperature response at lower temperatures (-5 to 10 degrees C) rather than to a temperature increase. This study shows that changes in ecosystem functioning can have a larger impact on the carbon balance than climate warming per se. (C) 2016 Elsevier B.V. All rights reserved.
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| 15. |
- Hadden, David, et al.
(author)
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Net CO2 emissions from a primary boreo-nemoral forest over a 10 year period
- 2017
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In: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 398, s. 164-173
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Journal article (peer-reviewed)abstract
- Primary forests play an important role in the global carbon balance. With little to no human intervention, primary forests are shaped and characterised by disturbances such as weather extremes, fire, insect and pathogen attacks. Such disturbances have a direct impact on the volume of coarse woody debris (CWD) which contributes to the total ecosystem respiration (Re). There are currently few studies that present continuous long term measurements of the carbon balance of northern primary forests. We used the eddy covariance method to measure continuous carbon dioxide (CO2) fluxes from a Swedish primary boreo-nemoral forest over a ten year period. By mapping the measured CO2 fluxes to the forest ecosystem we could indicate that small areas that had some form of disturbance and areas with significant levels of CWD within the eddy covariance footprint contributed to the total Re resulting in the forest being a net carbon source. A weighing algorithm, was used to account for directional ecosystem heterogeneity and to estimate a representative carbon balance for the ecosystem. The forest ecosystem was a continuous source of CO2 to the atmosphere, losing around 25 Mg per hectare of CO2 over a ten year period. (C) 2017 Elsevier B.V. All rights reserved.
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| 16. |
- Hadden, David, et al.
(author)
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The impact of cultivation on CO2 and CH4 fluxes over organic soils in Sweden
- 2017
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 243, s. 1-8
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Journal article (peer-reviewed)abstract
- Cultivated organic soils are large contributors to global greenhouse gas emissions. We measured carbon dioxide (CO2) and methane (CH4) fluxes from two organic soil plots in central Sweden between 2012 and 2016 using the eddy covariance technique. One site was cultivated whilst the other was set aside with no cultivation occurring. The aim was to establish the impact that cultivation had on the carbon balance. Over the five year period the set aside field acted as a net carbon source whilst the cultivated site was seen to be a small carbon sink. The set aside was further seen to act as a small methane sink over a 36 month period, which reduced the CO2 source by ca. 10% in terms of CO2 equivalents. Considering exported biomass, both sites were carbon sources in terms of Net Biome Production (NBP).
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| 17. |
- Haesen, Stef, et al.
(author)
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ForestClim : Bioclimatic variables for microclimate temperatures of European forests
- 2023
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In: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 29:11, s. 2886-2892
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Journal article (peer-reviewed)abstract
- Microclimate research gained renewed interest over the last decade and its importance for many ecological processes is increasingly being recognized. Consequently, the call for high-resolution microclimatic temperature grids across broad spatial extents is becoming more pressing to improve ecological models. Here, we provide a new set of open-access bioclimatic variables for microclimate temperatures of European forests at 25 x 25 m2 resolution.
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| 18. |
- Hagenbo, Andreas, 1987-, et al.
(author)
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Carbon use efficiency of mycorrhizal fungal mycelium increases during the growing season but decreases with forest age across a Pinus sylvestris chronosequence
- 2019
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In: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 107:6, s. 2808-2822
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Journal article (peer-reviewed)abstract
- In boreal forest soils, mycelium of mycorrhizal fungi is pivotal for regulating soil carbon (C) cycling and storage. The carbon use efficiency (CUE), a key parameter in C cycling models, can inform on the partitioning of C between microbial biomass, and potential soil storage, and respiration. Here, we test the dependency of mycorrhizal mycelial CUE on stand age and seasonality in managed boreal forest stands. Based on mycelial production and respiration estimates, derived from sequentially incubated ingrowth mesh bags, we estimated CUE on an ecosystem scale during a seasonal cycle and across a chronosequence of eight, 12- to 158-year-old, managed Pinus sylvestris forest stands characterized by decreasing pH and nitrogen (N) availability with increasing age. Mycelial respiration was related to total soil respiration, and by using eddy covariance flux measurements, primary production (GPP) was estimated in the 12- and 100-year-old forests, and related to mycelial respiration and CUE. As hypothesized, mycelial CUE decreased significantly with increasing forest age by c. 65%, supposedly related to a shift in mycorrhizal community composition and a metabolic adjustment reducing their own biomass N demand with declining soil N availability. Furthermore, mycelial CUE increased by a factor of five over the growing season; from 0.03 in May to 0.15 in November, and we propose that the seasonal change in CUE is regulated by a decrease in photosynthate production and temperature. The respiratory contribution of mycorrhizal mycelium ranged from 14% to 26% of total soil respiration, and was on average 17% across all sites and occasions. Synthesis. Carbon is retained more efficiently in mycorrhizal mycelium late in the growing season, when fungi have access to a more balanced C and nutrient supplies. Earlier in the growing season, at maximum host plant photosynthesis, when below-ground C availability is high in relation to N, the fungi respire excess C resulting in lower mycelial carbon use efficiency (CUE). Additionally, C is retained less efficiently in mycorrhizal fungal biomass in older forest stands characterized by more nutrient depleted soils than younger forest stands.
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| 19. |
- Kasurinen, Ville, et al.
(author)
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Latent heat exchange in the boreal and arctic biomes
- 2014
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 20:11, s. 3439-3456
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Research review (peer-reviewed)abstract
- In this study latent heat flux (E) measurements made at 65 boreal and arctic eddy-covariance (EC) sites were analyses by using the Penman-Monteith equation. Sites were stratified into nine different ecosystem types: harvested and burnt forest areas, pine forests, spruce or fir forests, Douglas-fir forests, broadleaf deciduous forests, larch forests, wetlands, tundra and natural grasslands. The Penman-Monteith equation was calibrated with variable surface resistances against half-hourly eddy-covariance data and clear differences between ecosystem types were observed. Based on the modeled behavior of surface and aerodynamic resistances, surface resistance tightly control E in most mature forests, while it had less importance in ecosystems having shorter vegetation like young or recently harvested forests, grasslands, wetlands and tundra. The parameters of the Penman-Monteith equation were clearly different for winter and summer conditions, indicating that phenological effects on surface resistance are important. We also compared the simulated E of different ecosystem types under meteorological conditions at one site. Values of E varied between 15% and 38% of the net radiation in the simulations with mean ecosystem parameters. In general, the simulations suggest that E is higher from forested ecosystems than from grasslands, wetlands or tundra-type ecosystems. Forests showed usually a tighter stomatal control of E as indicated by a pronounced sensitivity of surface resistance to atmospheric vapor pressure deficit. Nevertheless, the surface resistance of forests was lower than for open vegetation types including wetlands. Tundra and wetlands had higher surface resistances, which were less sensitive to vapor pressure deficits. The results indicate that the variation in surface resistance within and between different vegetation types might play a significant role in energy exchange between terrestrial ecosystems and atmosphere. These results suggest the need to take into account vegetation type and phenology in energy exchange modeling.
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| 20. |
- Keck, Hannes, et al.
(author)
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Setting-aside cropland did not reduce greenhouse gas emissions from a drained peat soil in Sweden
- 2024
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In: Frontiers in Environmental Science. - : Frontiers Media S.A.. - 2296-665X. ; 12
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Journal article (peer-reviewed)abstract
- In the process of their formation, northern peatlands were accumulating vast amounts of carbon (C). When drained for agricultural use, a large proportion of that C is oxidized and emitted as carbon dioxide (CO2), turning those peatlands to strong CO2 emitters. As a mitigation option, setting-aside farmland on drained peat is being incentivized by policies, but recent evidence casts doubt on these policies' efficiency for greenhouse gas (GHG) emission mitigation. To investigate the effects of setting-aside farmland on GHG fluxes from a Swedish peatland, we measured CO2, nitrous oxide (N2O), and methane (CH4) fluxes on two adjacent sites under contrasting management. The cultivated (CL) site was used for cereal production (wheat or barley) and the set-aside (SA) site was under permanent grassland. Carbon dioxide fluxes were measured from 2013 to 2019 using the eddy covariance (EC) method. Additionally, CO2, N2O, and CH4 fluxes were measured during the growing seasons of 2018-2020, using transparent and opaque chambers on vegetated plots and on bare peat. The cumulative CO2 fluxes measured by EC over the measurement period were 0.97 (+/- 0.05) and 2.09 (+/- 0.17) kg m-2 with annual average losses of 0.16 and 0.41 kg CO2 m-2 yr-1 for the CL and SA site, respectively. Thus, the SA site acted as a stronger CO2 source than the CL site. Both sites' contribution to global warming, calculated on basis of the chamber measurements, was dominated by CO2. The contribution of the SA site was higher than that of the CL site. Nitrous oxide emissions were low at both sites with higher emissions from the CL site for transparent measurements and measurements on bare peat. Whereas, CH4 uptake was highest on the SA grassland. Thus, on the basis of our study, we found no evidence that setting-aside farmland on shallow drained peat soils will reduce GHG emissions or even turn the peatland into a C sink.
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| 21. |
- Lagergren, Fredrik, et al.
(author)
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Current carbon balance of the forested area in Sweden and its sensitivity to global change as simulated by Biome-BGC
- 2006
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In: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 9:6, s. 894-908
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Journal article (peer-reviewed)abstract
- Detailed information from the Swedish National Forest Inventory was used to simulate the carbon balance for Sweden by the process-based model Biome-BGC. A few shortcomings of the model were identified and solutions to those are proposed and also used in the simulations. The model was calibrated against CO2 flux data from 3 forests in central Sweden and then applied to the whole country divided into 30 districts and 4 age classes. Gross primary production (GPP) ranged over districts and age classes from 0.20 to 1.71 kg C m(-2) y(-1) and net ecosystem production (NEP) ranged from -0.01 to 0.44. The 10- to 30-year age class was the strongest carbon sink because of its relatively low respiration rates. When the simulation results were scaled up to the whole country, GPP and NEP were 175 and 29 Mton C y(-1), respectively, for the 22.7 Mha of forests in Sweden. A climate change scenario was simulated by assuming a 4 degrees C increase in temperature and a doubling of the CO2 concentration; GPP and NEP then increased to 253 and 48 Mton C y(-1), respectively. A sensitivity analysis showed that at present CO2 concentrations NEP would peak at an increase of 5 degrees C for the mean annual temperature. At higher CO2 levels NEP showed a logarithmic increase.
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| 22. |
- Lankreijer, Harry, et al.
(author)
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Evaporation and storage of intercepted rain analysed by comparing two models applied to a boreal forest
- 1999
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In: Agricultural and Forest Meteorology. - 0168-1923 .- 1873-2240. ; 98-99, s. 595-604
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Journal article (peer-reviewed)abstract
- Rainfall and throughfall were measured during the summer of 1995. Rainfall interception is often simulated by a version of the well-known Rutter-Gash analytical model. In this study this model was compared to a model based on an exponential saturation equation. The concept of the ‘minimum method' for deriving canopy storage capacity and free throughfall coefficient by the Leyton-analysis, is compared to the concept of maximum storage capacity by reversing the models. Measured evaporation rate during rain events was found to be lower than simulated by the Penman equation using different known formulations for aerodynamic resistance. The concept of a high internal canopy resistance and decoupling of the canopy from the atmosphere should be analysed further in order to explain low evaporation during rainfall.
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| 23. |
- Launiainen, Samuli, et al.
(author)
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Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?
- 2016
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 22:12, s. 4096-4113
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Journal article (peer-reviewed)abstract
- Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (Gs), water- and light-use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy-covariance (EC) energy and CO2 fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk Gs representation. The LAI variations significantly alter radiation regime, within-canopy microclimate, sink/source distributions of CO2, H2O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem-scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry-canopy evapotranspiration (ET) was reasonably ‘conservative’ over the studied LAI range 0.5–7.0 m2 m−2. Both ET and Gs experienced a minimum in the LAI range 1–2 m2 m−2 caused by opposing nonproportional response of stomatally controlled transpiration and ‘free’ forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m2 m−2) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI <3 m2 m−2). This finding emphasizes the significance of stand-replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light-saturated water-use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests.
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| 24. |
- Lembrechts, Jonas J., et al.
(author)
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Global maps of soil temperature
- 2022
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:9, s. 3110-3144
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Journal article (peer-reviewed)abstract
- Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2m 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 5–15cm 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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| 25. |
- Lindroth, Anders, et al.
(author)
-
Storms can cause Europe-wide reduction in forest carbon sink
- 2009
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 15:2, s. 346-355
-
Journal article (peer-reviewed)abstract
- Disturbance of ecosystems is a major factor in regional carbon budgets, and it is believed to be partly responsible for the large inter-annual variability of the terrestrial part of the carbon balance. Forest fires have so far been considered as the most important disturbance but also other forms of disturbance such as insect outbreaks or wind-throw might contribute significantly to the largely unexplained inter-annual variability, at least in specific regions. The effect of wind-throw has not yet been estimated because of lack of data on how carbon fluxes are affected. The Gudrun storm, which hit Sweden in January 2005, resulted in ca. 66 million m(3) of wind-thrown stem wood on an area of ca. 272 000 ha. Using a model (BIOME-BGC) calibrated to CO2 flux measurements at two sites, the annual net ecosystem productivity during the first year after the storm was estimated to be in the range -897 to -1259 g C m(-2) yr(-1). This is a much higher loss compared with harvested (clear-cut) forests in Europe, which ranged between ca. -420 and -100 g m(-2) yr(-1). The reduction in the carbon sink scaled to the whole wind-thrown area was estimated at ca. 3 million tons C during the first year. By historical data on wind-throw in Europe combined with modelling, we estimated that the large Lothar storm in 1999 reduced the European carbon balance by ca. 16 million tons C, this is ca. 30% of the net biome production in Europe. We conclude that the impact of increased forest damage by more frequent storms in future climate change scenarios must be considered and that intermittent large wind-throw events may explain a part of the large inter-annual variability in the terrestrial carbon sink.
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| 26. |
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| 27. |
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| 28. |
- Meyer, Astrid, et al.
(author)
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A fertile peatland forest does not constitute a major greenhouse gas sink
- 2013
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 7739-7758
-
Journal article (peer-reviewed)abstract
- Afforestation has been proposed as a strategy to mitigate the often high greenhouse gas (GHG) emissions from agricultural soils with high organic matter content. However, the carbon dioxide (CO2) and nitrous oxide (N2O) fluxes after afforestation can be considerable, depending predominantly on site drainage and nutrient availability. Studies on the full GHG budget of afforested organic soils are scarce and hampered by the uncertainties associated with methodology. In this study we etermined the GHG budget of a spruce-dominated forest on a drained organic soil with an agricultural history. Two different approaches for determining the net ecosystem CO2 exchange (NEE) were applied, for the year 2008, one direct (eddy covariance) and the other indirect (analyzing the different components of the GHG budget), so that uncertainties in each method could be evaluated. The annual tree production in 2008 was 8.3±3.9 tC ha−1 yr−1 due to the high levels of soil nutrients, the favorable climatic conditions and the fact that the forest was probably in its phase of maximum C assimilation or shortly past it. The N2O fluxes were determined by the closed-chamber technique and amounted to 0.9±0.8 tCeq ha−1 yr−1. According to the direct measurements from the eddy covariance technique, the site acts as a minor GHG sink of −1.2±0.8 t Ceq ha−1 yr−1. This contrasts with the NEE estimate derived from the indirect approach which suggests that the site is a net GHG emitter of 0.6±4.5 tCeq ha−1 yr−1. Irrespective of the approach applied, the soil CO2 effluxes counter large amounts of the C sequestration by trees. Due to accumulated uncertainties involved in the indirect approach, the direct approach is considered the more reliable tool. As the rate of C sequestration will likely decrease with forest age, the site will probably become a GHG source once again as the trees do not compensate for the soil C and N losses. Also forests in younger age stages have been shown to have lower C assimilation rates; thus, the overall GHG sink potential of this afforested nutrient-rich organic soil is probably limited to the short period of maximum C assimilation.
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| 29. |
- Mjöfors, Kristina, et al.
(author)
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Stubbskörd och markens koldioxidbalans
- 2017
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In: Stubbskörd - hur påverkas klimat och miljö?. - 9789157694546 - 9789157694553 ; , s. 35-37
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Book chapter (other academic/artistic)abstract
- Markstörningar, som stubbskörd och markberedning, leder initialt till minskad koldioxidavgång från marken, visar en serie nya försök. Det är tvärtemot vad man tidigare har antagit. Efter det första året ligger avgången på ungefär samma nivå för störd mark som för ostörd.
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| 30. |
- Mjöfors, Kristina, et al.
(author)
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Stump harvesting and the soil/atmosphere exchange of CO2
- 2017
-
In: Stump Harvesting : Impacts on Climate and Environment - Impacts on Climate and Environment. ; , s. 33-37
-
Book chapter (other academic/artistic)abstract
- Soil disturbance from stump extraction and site preparation will initially lead to a reduction in carbon dioxide emissions from the soil. This is one result achieved from a series of new experiments established throughout Sweden and is contrasting to what was previously assumed. After one year however, this initial reduction had disappeared and emissions were around the same level for bothdisturbed and undisturbed soil.
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| 31. |
- Nemitz, E, et al.
(author)
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Standardisation of eddy-covariance flux measurements of methane and nitrous oxide
- 2018
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In: International Agrophysics. - : Walter de Gruyter GmbH. - 0236-8722 .- 2300-8725. ; 32, s. 517-549
-
Journal article (peer-reviewed)abstract
- Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long-term flux measurements with the eddycovariance method more feasible. Unlike for carbon dioxide (CO2) and water vapour (H2O), there have so far been no guidelines on how to optimise and standardise the measurements. This paper reviews the state-of-the-art of the various steps of the measurements and discusses aspects such as instrument selection, setup and maintenance, data processing as well as the additional measurements needed to aid interpretation and gap-filling. It presents the methodological protocol for eddy covariance measurements of CH4 and N2O fluxes as agreed for the ecosystem station network of the pan-European Research Infrastructure Integrated Carbon Observation System and provides a first international standard that is suggested to be adopted more widely. Fluxes can be episodic and the processes controlling the fluxes are complex, preventing simple mechanistic gap-filling strategies. Fluxes are often near or below the detection limit, requiring additional care during data processing. The protocol sets out the best practice for these conditions to avoid biasing the results and long-term budgets. It summarises the current approach to gap-filling.
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| 32. |
- Nilsson, Mats, et al.
(author)
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Contemporary carbon accumulation in a boreal oligotrophic minerogenic mire - a significant sink after accounting for all C-fluxes
- 2008
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 14:10, s. 2317-2332
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Journal article (peer-reviewed)abstract
- Based on theories of mire development and responses to a changing climate, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the current net C-exchange in mires requires measurements of all relevant fluxes. Estimates of annual total carbon budgets in mires are still very limited. Here, we present a full carbon budget over 2 years for a boreal minerogenic oligotrophic mire in northern Sweden (64 degrees 11'N, 19 degrees 33'E). Data on the following fluxes were collected: land-atmosphere CO2 exchange (continuous Eddy covariance measurements) and CH4 exchange (static chambers during the snow free period); TOC (total organic carbon) in precipitation; loss of TOC, dissolved inorganic carbon (DIC) and CH4 through stream water runoff (continuous discharge measurements and regular C-concentration measurements). The mire constituted a net sink of 27 +/- 3.4 (+/- SD) g C m(-2) yr(-1) during 2004 and 20 +/- 3.4 g C m(-2) yr(-1) during 2005. This could be partitioned into an annual surface-atmosphere CO2 net uptake of 55 +/- 1.9 g C m(-2) yr(-1) during 2004 and 48 +/- 1.6 g C m(-2) yr(-1) during 2005. The annual NEE was further separated into a net uptake season, with an uptake of 92 g C m(-2) yr(-1) during 2004 and 86 g C m(-2) yr(-1) during 2005, and a net loss season with a loss of 37 g C m(-2) yr(-1) during 2004 and 38 g C m(-2) yr(-1) during 2005. Of the annual net CO2-C uptake, 37% and 31% was lost through runoff (with runoff TOC > DIC >> CH4) and 16% and 29% through methane emission during 2004 and 2005, respectively. This mire is still a significant C-sink, with carbon accumulation rates comparable to the long-term Holocene C-accumulation, and higher than the C-accumulation during the late Holocene in the region.
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| 33. |
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| 34. |
- Peichl, Matthias, et al.
(author)
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A 12-year record reveals pre-growing season temperature and water table level threshold effects on the net carbon dioxide exchange in a boreal fen
- 2014
-
In: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 9:5
-
Journal article (peer-reviewed)abstract
- This study uses a 12-year time series (2001-2012) of eddy covariance measurements to investigate the long-term net ecosystem exchange (NEE) of carbon dioxide (CO2) and inter-annual variations in relation to abiotic drivers in a boreal fen in northern Sweden. The peatland was a sink for atmospheric CO2 in each of the twelve study years with a 12-year average (+/- standard deviation) NEE of -58 +/- 21 g C m(-2) yr(-1). For ten out of twelve years, the cumulative annual NEE was within a range of -42 to -79 g C m(-2) yr(-1) suggesting a general state of resilience of NEE to moderate inter-annual climate variations. However, the annual NEE of -18 and -106 g C m(-2) yr(-1) in 2006 and 2008, respectively, diverged considerably from this common range. The lower annual CO2 uptake in 2006 was mainly due to late summer emissions related to an exceptional drop in water table level (WTL). A positive relationship (R-2 = 0.65) between pre-growing season (January to April) air temperature (Ta) and summer (June to July) gross ecosystem production (GEP) was observed. We suggest that enhanced GEP due to mild pre-growing season air temperature in combination with air temperature constraints on ecosystem respiration (ER) during the following cooler summer explained most of the greater net CO2 uptake in 2008. Differences in the annual and growing season means of other abiotic variables (e.g. radiation, vapor pressure deficit, precipitation) and growing season properties (i.e. start date, end date, length) were unable to explain the inter-annual variations of NEE. Overall, our findings suggest that this boreal fen acts as a persistent contemporary sink for atmospheric CO2 that is, however, susceptible to severe anomalies in WTL and pre-growing season air temperature associated with predicted changes in climate patterns for the boreal region.
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| 35. |
- Peichl, Matthias, et al.
(author)
-
Energy exchange and water budget partitioning in a boreal minerogenic mire
- 2013
-
In: Journal of Geophysical Research. - 2156-2202. ; 118, s. 1-13
-
Journal article (peer-reviewed)abstract
- This study investigated patterns and controls of the seasonal and inter-annual variations in energy fluxes (i.e., sensible heat, H, and latent heat, lambda E) and partitioning of the water budget (i.e., precipitation, P; evapotranspiration, ET; discharge, Q; and soil water storage, Delta S) over five years (2001-2005) in a boreal oligotrophic fen in northern Sweden based on continuous eddy covariance, water table level (WTL), and weir measurements. For the growing season (May 1 to September 31), the 5 year averages (+/- standard deviation) of the midday (10:00 to 14:00 h) Bowen ratio (beta, i.e., H/lambda E) was 0.86 +/- 0.08. Seasonal and inter-annual variability of beta was mainly driven by lambda E which itself was strongly controlled by both weather (i.e., vapor pressure deficit, D, and net radiation, R-n) and physiological parameters (i.e., surface resistance). During the growing season, surface resistance largely exceeded aerodynamic resistance, which together with low mean values of the actual ET to potential ET ratio (0.55 +/- 0.05) and Priestley-Taylor alpha (0.89) suggests significant physiological constrains on ET in this well-watered fen. Among the water budget components, the inter-annual variability of ET was lower (199 to 298 mm) compared to Q (225 to 752 mm), with each accounting on average for 34 and 65% of the ecosystem water loss, respectively. The fraction of P expended into ET was negatively correlated to P and positively to R-n. Although a decrease in WTL caused a reduction of the surface conductance, the overall effect of WTL on ET was limited. Non-growing season (October 1 to April 30) fluxes of H, lambda E, and Q were significant representing on average -67%, 13%, and 61%, respectively, of their growing season sums (negative sign indicates opposite flux direction between the two seasons). Overall, our findings suggest that plant functional type composition, P and R-n dynamics (i.e., amount and timing) were the major controls on the partitioning of the mire energy and water budgets. This has important implications for the regional climate as well as for ecosystem development, nutrient, and carbon dynamics. Citation: Peichl, M., J. Sagerfors, A. Lindroth, I. Buffam, A. Grelle, L. Klemedtsson, H. Laudon, and M. B. Nilsson (2013), Energy exchange and water budget partitioning in a boreal minerogenic mire, J. Geophys. Res. Biogeosci., 118, 1-13, doi:10.1029/2012JG002073.
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| 36. |
- Peichl, Matthias, et al.
(author)
-
The ABCflux database: Arctic-boreal CO2 flux observations and ancillary information aggregated to monthly time steps across terrestrial ecosystems
- 2022
-
In: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 14, s. 179-208
-
Journal article (peer-reviewed)abstract
- Past efforts to synthesize and quantify the magnitude and change in carbon dioxide (CO2) fluxes in terrestrial ecosystems across the rapidly warming Arctic-boreal zone (ABZ) have provided valuable information but were limited in their geographical and temporal coverage. Furthermore, these efforts have been based on data aggregated over varying time periods, often with only minimal site ancillary data, thus limiting their potential to be used in large-scale carbon budget assessments. To bridge these gaps, we developed a standardized monthly database of Arctic-boreal CO2 fluxes (ABCflux) that aggregates in situ measurements of terrestrial net ecosystem CO2 exchange and its derived partitioned component fluxes: gross primary productivity and ecosystem respiration. The data span from 1989 to 2020 with over 70 supporting variables that describe key site conditions (e.g., vegetation and disturbance type), micrometeorological and environmental measurements (e.g., air and soil temperatures), and flux measurement techniques. Here, we describe these variables, the spatial and temporal distribution of observations, the main strengths and limitations of the database, and the potential research opportunities it enables. In total, ABCflux includes 244 sites and 6309 monthly observations; 136 sites and 2217 monthly observations represent tundra, and 108 sites and 4092 observations represent the boreal biome. The database includes fluxes estimated with chamber (19 % of the monthly observations), snow diffusion (3 %) and eddy covariance (78 %) techniques. The largest number of observations were collected during the climatological summer (June-August; 32 %), and fewer observations were available for autumn (September-October; 25 %), winter (December-February; 18 %), and spring (March-May; 25 %). ABCflux can be used in a wide array of empirical, remote sensing and modeling studies to improve understanding of the regional and temporal variability in CO2 fluxes and to better estimate the terrestrial ABZ CO2 budget. ABCflux is openly and freely available online (Virkkala et al., 2021b, https://doi.org/10.3334/ORNLDAAC/1934).
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| 37. |
- Piao, Shilong, et al.
(author)
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Net carbon dioxide losses of northern ecosystems in response to autumn warming
- 2008
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 451:7174, s. 3-49
-
Journal article (peer-reviewed)abstract
- The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring(1-4), with spring and autumn temperatures over northern latitudes having risen by about 1.1 degrees C and 0.8 degrees C, respectively, over the past two decades(5). A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity(6,7). These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future(8). Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn- to- winter carbon dioxide build- up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process- based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC degrees C-1, offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested(9,10).
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| 38. |
- Schubert, Per, et al.
(author)
-
Modeling GPP in the Nordic forest landscape with MODIS time series data-Comparison with the MODIS GPP product
- 2012
-
In: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 126, s. 136-147
-
Journal article (peer-reviewed)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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| 39. |
- Strömgren, Monika, et al.
(author)
-
Nya och gamla fältförsök med stubbskörd
- 2017
-
In: Stubbskörd - hur påverkas klimat och miljö?. - 9789157694546 ; , s. 26-29
-
Book chapter (pop. science, debate, etc.)abstract
- Merparten av det vi i dag vet om stubbskördens miljöeffekter kommer från fyra stora försöksserier med totalt 33 fältförsök spridda över landet. Till detta kommer fyra enskilda försök. De äldsta försöken är från sent 1970-tal, men merparten är relativt nyetablerade.
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| 40. |
- Strömgren, Monika, et al.
(author)
-
Soil CO2 Flux During the First Years After Stump Harvesting in Two Swedish Forests
- 2012
-
In: Silva Fennica. - : Finnish Society of Forest Science. - 0037-5330 .- 2242-4075. ; 46, s. 67-79
-
Journal article (peer-reviewed)abstract
- One way of increasing the supply of renewable energy, thereby decreasing the use of fossil fuels, is to extract the stumps that remain after final stem harvesting. However, little is known about the environmental consequences of stump harvesting, and how ecosystem services, such as carbon sequestration, are affected by the practice. In the present paper, the effects on the soil carbon pool during the first months and years after stump harvesting in former Norway spruce stands are presented. The study was performed at two sites in mid- and southern Sweden. At both sites, the soil CO2 flux was measured on several occasions with a portable respiration system, to compare plots on which stump harvesting had occurred, with reference plots. At one of the sites, CO2 exchange was also followed continuously by means of eddy-covariance measurements before and after stump harvesting. Since there was no vegetation at the beginning of the study, almost all emitted CO2 could be assumed to come from heterotrophic sources, and the soil CO2 flux was measured. This study shows that the effect of stump harvesting on CO2 flux or soil decomposition processes is small or absent compared to site preparation such as mounding in a short-term perspective of months and years. The long-term consequences of stump harvesting are, however, still uncertain.
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| 41. |
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| 42. |
- Öquist, Mats, et al.
(author)
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The full annual carbon balance of boreal forestsis highly sensitive to precipitation
- 2014
-
In: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 1:7, s. 315-319
-
Journal article (peer-reviewed)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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