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Long term studies of effects of climate manipulations on subarctic ecosystems

Since June 2000, we have been conducting a field manipulation experiment simulating climate scenarios in a subarctic Sphagnum-dominated blanket bog near Abisko, N Sweden. This experiment is unique in that it mimics six different combinations of (current and predicted) spring, summer and winter climate, each replicated five times. Passive spring and summer warming is achieved through transparent tent-like open-top chambers (OTC, 2.5 m diameter). In winter the same OTCs are effectively used to capture and retain snow, which in this wind-exposed site is often blown away from ambient plots but into the OTCs. The statistical design is factorial, i.e. there are 30 OTCs. i.e. 15 + 15 OTCs for ambient and warmed summer treatment and, within each summer treatment 5 for ambient spring and winter conditions, 5 with ambient spring but OTC in winter, and 5 with OTC both in spring. The replicates are organized in blocks each containing all 6 treatments. Here we are measuring or have measured a range of features of the microclimate, soil (peat) properties, vegetation composition, diversity, structure and growth, carbon and nutrient exchange parameters, aspects of species responses (plants, microbes, soil invertebrates). The experiment, which is planned to run until at least 2020, is embedded in international scientific networks for global change investigations, for instance the International Tundra Experiment (ITEX). Datasets have been or are being assembled for: - microclimate in the different treatments, including continuous recording of soil temperatures (ongoing) and (2000-2005) air temperatures; weekly snow depth; soil moisture and air humidity (in specific years); permafrost depth (active layer depth); - soil (peat) properties at different depths; - vegetation structure and composition down to species level, both vascular plants and cryptogams (2-yearly, through point-frame recording with associated biomass calibrations); - plant species and functional diversity - Sphagnum growth (in several specific years) - annual shoot increments of target vascular species (in specific years) - vegetative and reproductive phenology - nutrient recycling, e.g. through resorption processes - litter decomposition rates at the ecosystem and species level (environmental and species effects on decomposition; specific years) - ecosystem level carbon exchange including soil respiration and photosynthesis; 13C signatures as indicators of respiration responses to warming for different peat horizons - microbial community composition with special focus on their contributions on different nitrogen-transforming functions - community composition of invertebrate soil fauna (Collembola, mites) and Thecamoebic protozoans (both being prepared).

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