29th Conf. on Agricultural and Forest Meteorology/19th Symp. on Boundary Layers and Turbulence/Ninth Symp. on the Urban Environment (1-6 August 2010), Aug 6, 2010
Regional climate models predict an intensification of extreme heat waves in Central Europe. Again... more Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increas-ing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are pre-sented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The in-vestigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of K...
Das Meteorologische Institut der Universität Freiburg betreibt im Rahmen des Sonderfor-schungsber... more Das Meteorologische Institut der Universität Freiburg betreibt im Rahmen des Sonderfor-schungsbereiches (SFB) 433 Buchendominierte Laubwälder unter dem Einfluss von Klima und Bewirtschaftung fünf mikrometeorologische Messstationen auf den gemeinsamen SFB- ...
Philosophical Transactions of the Royal Society B: Biological Sciences
The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and la... more The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of...
The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management polic... more The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management policies to mitigate anthropogenic emissions of greenhouse gases (GHG). The net effects of forest management on the climate and the environment are, however, still not completely understood, partially as a result of a lack of long-term measurements of GHG fluxes in managed forests. During the period 2010–2013, we simultaneously measured carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes using the flux-gradient technique at two clear-cut plots of different degrees of wetness, located in central Sweden. The measurements started approx. one year after clear-cutting, directly following soil scarification and planting. The study focused on robust inter-plot comparisons, spatial and temporal dynamics of GHG fluxes, and the determination of the global warming potential of a clear-cut boreal forest. The clear-cutting resulted in significant emissions of GHGs at both the wet and the dr...
<p>... more <p>We present the Net Ecosystem Carbon Balance (NECB) of a Northern mire ecosystem for the period 2016-2019. The Mycklemossen peatland is located in the hemi-boreal region in the Southwestern part of Sweden and is classified as a fen with bog-like vegetation. The NECB was determined from eddy covariance (EC) measurements of carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) and continuous water discharge measurements with biweekly measurements of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and dissolved CH<sub>4</sub>. <br>We focus on the carbon dynamics of the Mycklemossen ecosystem during summer droughts and on its recovery during normal years. During 2016-2018, the annual precipitation was lower than the 30-year average while 2019 was a normal year in terms of weather conditions. 2018 sticks out as an extreme year with a severe drought and unusually high air temperature at Mycklemossen, as was the case in much of Northern and Central Europe.<br>The EC results indicate that Mycklemossen lost carbon during 2016-2018. While CH<sub>4</sub> emissions decreased, the mire became a strong source of CO<sub>2</sub> these years, especially 2018. There were also large losses of DOC during this period, which were further enhanced during 2019.</p>
<p>... more <p>Arctic climate is warming twice as much as the global average, due to a number of climate system feedbacks, including albedo change due to retreating snow cover and sea ice, and the forest cover expansion across the open tundra. Northern ecosystems are known to emit trace gases (e.g., methane and volatile organic compounds, VOCs) to the atmosphere, from sources as diverse as soils, vegetation and lakes. These trace gas fluxes are likely to show a trend towards greater emissions with climate warming.</p><p>Here we report ecosystem-level VOC fluxes from Stordalen Mire, a subarctic peatland complex with a high fraction of open pond and lake surfaces, underlain by discontinuous permafrost and located in the Subarctic Sweden (68º20' N, 19º03' E).</p><p>In 2018, we deployed two online mass spectrometers (PTR-TOF-MS) to measure rapid fluctuations in VOC mixing ratios and to quantify ecosystem-level fluxes with the eddy covariance technique. One of the instruments obtained a growing-season-long dataset of biogenic emissions from palsa mire vegetation dominated by mosses (e.g., <em>Sphagnum</em> spp.), graminoids (such as <em>Eriophorum</em> spp. and <em>Carex</em> spp.), dwarf shrubs (e.g. Empetrum spp. and Betula nana) surrounding the ICOS Sweden Abisko-Stordalen long-term measurement station. The second instrument measured VOC fluxes during two contrasting periods (the peak and the end of the growing season) from a subarctic lake and its adjacent fen, permafrost-free, minerotrophic wetland with vegetation dominated by tall graminoids, mainly <em>Carex rostrata</em> and <em>Eriophorum angustifolium</em>.</p><p>At both sites, isoprene was the dominant VOC emitted by vegetation, showing clear diurnal patterns along the season and especially during the peak of the growing season in July. At the ICOS Sweden station, isoprene fluxes exceeded 2 nmol m<sup>-2</sup> s<sup>-1</sup> on several days in July, with a July monthly average midday emission of 1 nmol m<sup>-2</sup> s<sup>-1</sup>. The fen site showed average midday emissions of 2 nmol m<sup>-2</sup> s<sup>-1</sup> during the peak growing season. Other VOCs emitted by vegetation at both sites in July were, with decreasing magnitude, methanol, acetone, acetaldehyde and monoterpenes. In contrast, acetaldehyde and acetone were not emitted but…
<p>... more <p>In 2018, North-Western Europe experienced very dry and warm summer. These conditions can have considerable effects on the functioning and greenhouse gas exchange of terrestrial ecosystems. Peat-forming wetlands, or mires, are a characteristic component of the North-European boreal landscape, and crucial for long-term carbon storage as well as for methane emission. We have analyzed the effect of the drought on greenhouse gas (GHG) exchange of five North European mire ecosystems in Sweden and Finland in 2018. The low precipitation and high summer temperatures in Fennoscandia led to a lowered water table in majority of the mires. This lowered both carbon dioxide (CO<sub>2</sub>) uptake and methane (CH<sub>4</sub>) emission during 2018, turning many of the mires from CO<sub>2</sub>sinks to sources during this year. The changes in methane emission and total GHG exchange, expressed as CO<sub>2</sub>equivalent, were significantly correlated with change in water table position. The calculated time-evolving radiative forcing due to the changes in GHG fluxes in 2018 showed that the drought-induced changes in GHG fluxes first resulted in a cooling effect lasting 15-50 years, due to the lowered CH<sub>4</sub>emission, which was followed by longer-term warming phase due to the lower CO<sub>2 </sub>uptake in 2018.</p><p> </p>
&... more <p>In summer 2018, Northern Europe experienced an extreme summer drought in combination with unusually high temperatures, which had a substantial impact on agricultural yields as well as on forest growth conditions in various ways. An ongoing study, using ICOS and other forest ecosystem stations in the Nordic region, shows that the drought dramatically decreased NEP in the southern Scandinavian and Baltic region, almost nullifying the carbon sinks in some of the forests. However, some of the forests that not were exposed to the most extreme drought actually increased their NEP because of the high evaporative demand. Such severe conditions during a single year could be expected to influence a forest over several following years. Reduced tree storage of carbohydrates leads to a changed carbon allocation pattern in spring that may affect both the woody growth and the resistance to pests. It is thus important to reveal the impact of such climatic events over a longer period.    </p> <p>This study aims at assessing the carry-over effects of the extreme weather conditions on the carbon fluxes and the forest growth to the year after the event, 2019. The base of the analysis will be eddy covariance data combined with tree ring time series from measurement stations that has been shown to be significantly affected by the drought through reduced carbon fluxes: the spruce forests Hyltemossa and Skogaryd and the mixed forests Norunda, Svartberget, Soontaga and Rumperöd. The eddy covariance and tree ring data will be used to assess the forest ecosystem carbon fluxes and growth recovery in 2019 by comparisons to earlier normal years and extreme events.</p>
Based on human-biometeorological measurements at two different sites within a street canyon in th... more Based on human-biometeorological measurements at two different sites within a street canyon in the city of Freiburg (southwest Germany), the shading influence of the canopy of street trees on human thermal comfort was investigated for a typical Central European summer day ...
We developed a xylem water transport model for European beech (Fagus sylvatica L.) to scale up or... more We developed a xylem water transport model for European beech (Fagus sylvatica L.) to scale up organ based processes to the tree level and to quantify their influence on the whole tree transpiration and the water uptake from the soil. To better consider the root-soil interaction a finite ...
29th Conf. on Agricultural and Forest Meteorology/19th Symp. on Boundary Layers and Turbulence/Ninth Symp. on the Urban Environment (1-6 August 2010), Aug 6, 2010
Regional climate models predict an intensification of extreme heat waves in Central Europe. Again... more Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increas-ing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are pre-sented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The in-vestigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of K...
Das Meteorologische Institut der Universität Freiburg betreibt im Rahmen des Sonderfor-schungsber... more Das Meteorologische Institut der Universität Freiburg betreibt im Rahmen des Sonderfor-schungsbereiches (SFB) 433 Buchendominierte Laubwälder unter dem Einfluss von Klima und Bewirtschaftung fünf mikrometeorologische Messstationen auf den gemeinsamen SFB- ...
Philosophical Transactions of the Royal Society B: Biological Sciences
The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and la... more The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of...
The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management polic... more The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management policies to mitigate anthropogenic emissions of greenhouse gases (GHG). The net effects of forest management on the climate and the environment are, however, still not completely understood, partially as a result of a lack of long-term measurements of GHG fluxes in managed forests. During the period 2010–2013, we simultaneously measured carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes using the flux-gradient technique at two clear-cut plots of different degrees of wetness, located in central Sweden. The measurements started approx. one year after clear-cutting, directly following soil scarification and planting. The study focused on robust inter-plot comparisons, spatial and temporal dynamics of GHG fluxes, and the determination of the global warming potential of a clear-cut boreal forest. The clear-cutting resulted in significant emissions of GHGs at both the wet and the dr...
<p>... more <p>We present the Net Ecosystem Carbon Balance (NECB) of a Northern mire ecosystem for the period 2016-2019. The Mycklemossen peatland is located in the hemi-boreal region in the Southwestern part of Sweden and is classified as a fen with bog-like vegetation. The NECB was determined from eddy covariance (EC) measurements of carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) and continuous water discharge measurements with biweekly measurements of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and dissolved CH<sub>4</sub>. <br>We focus on the carbon dynamics of the Mycklemossen ecosystem during summer droughts and on its recovery during normal years. During 2016-2018, the annual precipitation was lower than the 30-year average while 2019 was a normal year in terms of weather conditions. 2018 sticks out as an extreme year with a severe drought and unusually high air temperature at Mycklemossen, as was the case in much of Northern and Central Europe.<br>The EC results indicate that Mycklemossen lost carbon during 2016-2018. While CH<sub>4</sub> emissions decreased, the mire became a strong source of CO<sub>2</sub> these years, especially 2018. There were also large losses of DOC during this period, which were further enhanced during 2019.</p>
<p>... more <p>Arctic climate is warming twice as much as the global average, due to a number of climate system feedbacks, including albedo change due to retreating snow cover and sea ice, and the forest cover expansion across the open tundra. Northern ecosystems are known to emit trace gases (e.g., methane and volatile organic compounds, VOCs) to the atmosphere, from sources as diverse as soils, vegetation and lakes. These trace gas fluxes are likely to show a trend towards greater emissions with climate warming.</p><p>Here we report ecosystem-level VOC fluxes from Stordalen Mire, a subarctic peatland complex with a high fraction of open pond and lake surfaces, underlain by discontinuous permafrost and located in the Subarctic Sweden (68º20' N, 19º03' E).</p><p>In 2018, we deployed two online mass spectrometers (PTR-TOF-MS) to measure rapid fluctuations in VOC mixing ratios and to quantify ecosystem-level fluxes with the eddy covariance technique. One of the instruments obtained a growing-season-long dataset of biogenic emissions from palsa mire vegetation dominated by mosses (e.g., <em>Sphagnum</em> spp.), graminoids (such as <em>Eriophorum</em> spp. and <em>Carex</em> spp.), dwarf shrubs (e.g. Empetrum spp. and Betula nana) surrounding the ICOS Sweden Abisko-Stordalen long-term measurement station. The second instrument measured VOC fluxes during two contrasting periods (the peak and the end of the growing season) from a subarctic lake and its adjacent fen, permafrost-free, minerotrophic wetland with vegetation dominated by tall graminoids, mainly <em>Carex rostrata</em> and <em>Eriophorum angustifolium</em>.</p><p>At both sites, isoprene was the dominant VOC emitted by vegetation, showing clear diurnal patterns along the season and especially during the peak of the growing season in July. At the ICOS Sweden station, isoprene fluxes exceeded 2 nmol m<sup>-2</sup> s<sup>-1</sup> on several days in July, with a July monthly average midday emission of 1 nmol m<sup>-2</sup> s<sup>-1</sup>. The fen site showed average midday emissions of 2 nmol m<sup>-2</sup> s<sup>-1</sup> during the peak growing season. Other VOCs emitted by vegetation at both sites in July were, with decreasing magnitude, methanol, acetone, acetaldehyde and monoterpenes. In contrast, acetaldehyde and acetone were not emitted but…
<p>... more <p>In 2018, North-Western Europe experienced very dry and warm summer. These conditions can have considerable effects on the functioning and greenhouse gas exchange of terrestrial ecosystems. Peat-forming wetlands, or mires, are a characteristic component of the North-European boreal landscape, and crucial for long-term carbon storage as well as for methane emission. We have analyzed the effect of the drought on greenhouse gas (GHG) exchange of five North European mire ecosystems in Sweden and Finland in 2018. The low precipitation and high summer temperatures in Fennoscandia led to a lowered water table in majority of the mires. This lowered both carbon dioxide (CO<sub>2</sub>) uptake and methane (CH<sub>4</sub>) emission during 2018, turning many of the mires from CO<sub>2</sub>sinks to sources during this year. The changes in methane emission and total GHG exchange, expressed as CO<sub>2</sub>equivalent, were significantly correlated with change in water table position. The calculated time-evolving radiative forcing due to the changes in GHG fluxes in 2018 showed that the drought-induced changes in GHG fluxes first resulted in a cooling effect lasting 15-50 years, due to the lowered CH<sub>4</sub>emission, which was followed by longer-term warming phase due to the lower CO<sub>2 </sub>uptake in 2018.</p><p> </p>
&... more <p>In summer 2018, Northern Europe experienced an extreme summer drought in combination with unusually high temperatures, which had a substantial impact on agricultural yields as well as on forest growth conditions in various ways. An ongoing study, using ICOS and other forest ecosystem stations in the Nordic region, shows that the drought dramatically decreased NEP in the southern Scandinavian and Baltic region, almost nullifying the carbon sinks in some of the forests. However, some of the forests that not were exposed to the most extreme drought actually increased their NEP because of the high evaporative demand. Such severe conditions during a single year could be expected to influence a forest over several following years. Reduced tree storage of carbohydrates leads to a changed carbon allocation pattern in spring that may affect both the woody growth and the resistance to pests. It is thus important to reveal the impact of such climatic events over a longer period.    </p> <p>This study aims at assessing the carry-over effects of the extreme weather conditions on the carbon fluxes and the forest growth to the year after the event, 2019. The base of the analysis will be eddy covariance data combined with tree ring time series from measurement stations that has been shown to be significantly affected by the drought through reduced carbon fluxes: the spruce forests Hyltemossa and Skogaryd and the mixed forests Norunda, Svartberget, Soontaga and Rumperöd. The eddy covariance and tree ring data will be used to assess the forest ecosystem carbon fluxes and growth recovery in 2019 by comparisons to earlier normal years and extreme events.</p>
Based on human-biometeorological measurements at two different sites within a street canyon in th... more Based on human-biometeorological measurements at two different sites within a street canyon in the city of Freiburg (southwest Germany), the shading influence of the canopy of street trees on human thermal comfort was investigated for a typical Central European summer day ...
We developed a xylem water transport model for European beech (Fagus sylvatica L.) to scale up or... more We developed a xylem water transport model for European beech (Fagus sylvatica L.) to scale up organ based processes to the tree level and to quantify their influence on the whole tree transpiration and the water uptake from the soil. To better consider the root-soil interaction a finite ...
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