Environmental change at the alpine treeline
High elevation ecosystems are important in research on environmental change because shifts in climate associated with anthropogenic greenhouse gas emissions are predicted to be more pronounced in these areas than in most other regions of the world. This project involves a Free Air CO2 Enrichment (FACE) and soil warming experiment located in a natural treeline environment near Davos, Switzerland (2200 m a.s.l.). The study site is located within the Stillberg long-term research site, where close to 100,000 trees were planted in 1975 (further information).
From 2001-2009, natural vegetation, including the two tree species Larix decidua (European larch, deciduous) and Pinus mugo ssp. uncinata (mountain pine, evergreen) and the dwarf shrub-dominated understorey, were exposed to elevated atmospheric CO2 concentrations (+200 ppm). A soil warming treatment (+4 K) was added in 2007 (final season 2012), resulting in a combination of CO2 enrichment and warming that is realistic for this region in approximately 2050. A broad range of ecological and biogeochemical research has been carried out as part of this environmental change project (further information).
With this experiment, we aimed to:
http://www.wsl.ch/fe/boden/projekte/stillberg/index_EN
High elevation ecosystems are important in research on environmental change because shifts in climate associated with anthropogenic greenhouse gas emissions are predicted to be more pronounced in these areas than in most other regions of the world. This project involves a Free Air CO2 Enrichment (FACE) and soil warming experiment located in a natural treeline environment near Davos, Switzerland (2200 m a.s.l.). The study site is located within the Stillberg long-term research site, where close to 100,000 trees were planted in 1975 (further information).
From 2001-2009, natural vegetation, including the two tree species Larix decidua (European larch, deciduous) and Pinus mugo ssp. uncinata (mountain pine, evergreen) and the dwarf shrub-dominated understorey, were exposed to elevated atmospheric CO2 concentrations (+200 ppm). A soil warming treatment (+4 K) was added in 2007 (final season 2012), resulting in a combination of CO2 enrichment and warming that is realistic for this region in approximately 2050. A broad range of ecological and biogeochemical research has been carried out as part of this environmental change project (further information).
With this experiment, we aimed to:
- Identify how and why tree and dwarf shrub growth and physiology change in response to increasing temperatures and CO2 concentration.
- Estimate how elevated CO2 and warming affect the competition between trees, dwarf shrubs, and grasses, and therefore the vegetation structure and composition.
- Determine if elevated CO2 and increased soil temperature alters plant sensitivity to freezing events during the growing season.
- Quantify the response of C fluxes (soil respiration, DOC leaching, accumulation in different SOM pools, aboveground biomass) and nutrient status.
- Study how the composition of the soil microbial community responds to elevated CO2 and warming.
- Elucidate if new plant-derived, rapidly cycling soil C fraction or older, slo cycling soil C responds more sensitively to climatic warming.
- Determine if soil warming alters the partitioning of recent assimilates between plants and soils.
- Study the transfer of carbon and nutrients between plants, soil and mycorrhiza.
- Test for the effect of atmospheric and climate change on seedling emergence and survival.
http://www.wsl.ch/fe/boden/projekte/stillberg/index_EN
Irrigation Experiment Pfynwald
In Switzerland, the temperature increase in the late 20th and beginning of the 21st century was more than twice the global average. Climate models predict a further increase during the 21st century and beyond. In correspondence with the warming-induced increase in evaporation, a change in water supply is expected with increased frequency of summer heatwaves, but also an increase in frequency and intensity of precipitation events with strong surface runoff, probably further enhancing drought stress for plants. Drought periods severely affect forest productivity, decrease tree vigor and reduce tree growth. Drought is an important trigger for forest decline, mortality and decline-induced vegetation shifts worldwide and in forest ecosystems in inner-Alpine dry valleys such as the Valais (Rigling et al. 2013).
The impact assessment of drought and drought release on forests is challenged by the complexity of these ecosystems and the longevity of the trees. Hence, large-scale drought experiments and long-term field measurements of plant water stress in young and mature forests are needed. Recently, Leuzinger et al. (2011) discussed the need of global change experiments and their restrictions with respect to i)degree of complexity depicted, ii) time scale, and iii) spatial coverage. It seems that many experiments overestimate the net ecosystem responses because of a too short time scales or due to the young age of investigated trees. Hence, larger-scale and fully coupled field experiments with longer time scales and mature trees are needed to study the impact of drought and drought release on forest ecosystems and their net responses.
To study the performance of mature Scots pine (Pinus sylvestris L.) under chronic drought conditions in comparison to their immediate physiological response to drought release, a controlled long-term and large-scale irrigation experiment was set up in 2003. The experiment is located in a xeric mature Scots pine forest in the Pfynwald (46º 18' N, 7º 36' E, 615 m a.s.l.) in one of the driest inner-Alpine valleys of the European Alps, the Valais (mean annual temperature: 9.2°C, annual precipitation sum: 657 mm, both 1961-1990). During April-October, irrigation is applied on four randomly selected plots, corresponding to a supplementary rainfall of 700 mm/year. Trees in the other four plots grow under naturally dry conditions. The duration of the irrigation experiment is 20 years, hence it will end in 2022.
http://www.wsl.ch/fe/walddynamik/projekte/irrigationpfynwald/index_EN
In Switzerland, the temperature increase in the late 20th and beginning of the 21st century was more than twice the global average. Climate models predict a further increase during the 21st century and beyond. In correspondence with the warming-induced increase in evaporation, a change in water supply is expected with increased frequency of summer heatwaves, but also an increase in frequency and intensity of precipitation events with strong surface runoff, probably further enhancing drought stress for plants. Drought periods severely affect forest productivity, decrease tree vigor and reduce tree growth. Drought is an important trigger for forest decline, mortality and decline-induced vegetation shifts worldwide and in forest ecosystems in inner-Alpine dry valleys such as the Valais (Rigling et al. 2013).
The impact assessment of drought and drought release on forests is challenged by the complexity of these ecosystems and the longevity of the trees. Hence, large-scale drought experiments and long-term field measurements of plant water stress in young and mature forests are needed. Recently, Leuzinger et al. (2011) discussed the need of global change experiments and their restrictions with respect to i)degree of complexity depicted, ii) time scale, and iii) spatial coverage. It seems that many experiments overestimate the net ecosystem responses because of a too short time scales or due to the young age of investigated trees. Hence, larger-scale and fully coupled field experiments with longer time scales and mature trees are needed to study the impact of drought and drought release on forest ecosystems and their net responses.
To study the performance of mature Scots pine (Pinus sylvestris L.) under chronic drought conditions in comparison to their immediate physiological response to drought release, a controlled long-term and large-scale irrigation experiment was set up in 2003. The experiment is located in a xeric mature Scots pine forest in the Pfynwald (46º 18' N, 7º 36' E, 615 m a.s.l.) in one of the driest inner-Alpine valleys of the European Alps, the Valais (mean annual temperature: 9.2°C, annual precipitation sum: 657 mm, both 1961-1990). During April-October, irrigation is applied on four randomly selected plots, corresponding to a supplementary rainfall of 700 mm/year. Trees in the other four plots grow under naturally dry conditions. The duration of the irrigation experiment is 20 years, hence it will end in 2022.
http://www.wsl.ch/fe/walddynamik/projekte/irrigationpfynwald/index_EN
Treeline changes and soil organic matter cycling in the Urals
Historic photographs document that treelines have shifted by 40 to 80 m during the last century. Our first results suggest that the upward shift in treeline has small net effects on C storage in soils, but speeds up SOM cycling and net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass.
Rationale
Treelines are natural boundary ecosystems where dominant plant species, life forms and plant productivity change drastically within a small altitudinal gradient and a short distance. In the Ural mountains, historic fixed-point landscape photographs document that positions of treeline have moved up by 60 to 80 m in altitude and that the forest of the treeline ecotone has become denser during the last century (Moiseev & Shiyatov, 2003; Devi et al., 2008). These changes of the forest-tundra ecotone very likely result from a changing climate since treelines positions are thought to be limited by vegetation period temperature and the highest mountains of the Urals had never been impacted by humans. Similar up- and northward shifts of treeline ecotones have been reported from North America, Scandinavia and Siberia, showing that these climate-induced advances occur in large areas of the Northern Hemisphere.
The advancing forest will alter soil microbial communities, and the carbon and nutrient cycling. It will increase C storage in forest biomass. Its effects on soil carbon, however, are less certain, since the upward-shifting treeline ecotone will not only change the quantity and quality of C inputs into soils, but also lead to a more favourable microclimate, which may stimulate respiration losses from soils.
Aims
In an ERA.NetRus-project we are investigating how the observed upward shift of the treeline ecotone affects biomass pools, above-and belowground diversity and soil C and N dynamics.
Methods
In our space for time-approach we determine biomass stocks, plant diversity, microbial communities, soil C and N pools as well as SOM quality along altitudinal gradients in the Southern Northern and Polar Urals, assuming that ecosystems at different altitudes reflect different stages of the upward shifting forest-tundra ecotone.
Results
Upward expansion occurs along the 1500 km long Ural mountains. Results indicate a change in tree growth forms during the last century from creeping krummholz to vertical single, stem trees. The primary climatic change is winter climate with more snowfall. The upward shift in treeline leads to a slow increase in tree biomass and has small net effects on C storage in soils. However, SOM cycling and net N mineralization is speeded up, which in turn might stimulate plant growth and thus C sequestration in tree biomass.
www.wsl.ch/de/projekte/treeline-in-ural-1.html
Historic photographs document that treelines have shifted by 40 to 80 m during the last century. Our first results suggest that the upward shift in treeline has small net effects on C storage in soils, but speeds up SOM cycling and net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass.
Rationale
Treelines are natural boundary ecosystems where dominant plant species, life forms and plant productivity change drastically within a small altitudinal gradient and a short distance. In the Ural mountains, historic fixed-point landscape photographs document that positions of treeline have moved up by 60 to 80 m in altitude and that the forest of the treeline ecotone has become denser during the last century (Moiseev & Shiyatov, 2003; Devi et al., 2008). These changes of the forest-tundra ecotone very likely result from a changing climate since treelines positions are thought to be limited by vegetation period temperature and the highest mountains of the Urals had never been impacted by humans. Similar up- and northward shifts of treeline ecotones have been reported from North America, Scandinavia and Siberia, showing that these climate-induced advances occur in large areas of the Northern Hemisphere.
The advancing forest will alter soil microbial communities, and the carbon and nutrient cycling. It will increase C storage in forest biomass. Its effects on soil carbon, however, are less certain, since the upward-shifting treeline ecotone will not only change the quantity and quality of C inputs into soils, but also lead to a more favourable microclimate, which may stimulate respiration losses from soils.
Aims
In an ERA.NetRus-project we are investigating how the observed upward shift of the treeline ecotone affects biomass pools, above-and belowground diversity and soil C and N dynamics.
Methods
In our space for time-approach we determine biomass stocks, plant diversity, microbial communities, soil C and N pools as well as SOM quality along altitudinal gradients in the Southern Northern and Polar Urals, assuming that ecosystems at different altitudes reflect different stages of the upward shifting forest-tundra ecotone.
Results
Upward expansion occurs along the 1500 km long Ural mountains. Results indicate a change in tree growth forms during the last century from creeping krummholz to vertical single, stem trees. The primary climatic change is winter climate with more snowfall. The upward shift in treeline leads to a slow increase in tree biomass and has small net effects on C storage in soils. However, SOM cycling and net N mineralization is speeded up, which in turn might stimulate plant growth and thus C sequestration in tree biomass.
www.wsl.ch/de/projekte/treeline-in-ural-1.html