Site location and background
The experimental site of Brandbjerg, Denmark (55°53'N 11°58'E) is situated on a hilly nutrient-poor sandy deposit in a semi-natural terrestrial ecosystem with dry heath/grassland vegetation dominated by the grass Deschampsia flexuosa and the evergreen dwarf shrub Calluna vulgaris. The mean annual temperature is 8.0 °C and the mean annual precipitation is approximately 620 mm.
Climate change manipulations
The experiment was initiated in October 2005 and includes treatments of elevated CO2 concentration (CO2), increased temperature (T), drought in late spring/summer (D), and untreated controls for reference (A). The treatments are applied singly and in all possible combinations (A, T, D, CO2, TD, TCO2, DCO2, TDCO2). Each experimental treatment is replicated six times, (total of 48 plots) in a split plot design with six octagons at ambient CO2 and six receiving elevated CO2 (See Figure). Each octagon spans 6.8 m and the individual treatment plots are 9.1 m2 in area. The distance between the octagons is at least 17 m, to prevent contamination of ambient CO2 plots by the neighbouring FACE system; the experiment is conducted within a fenced area of approximately 1 ha. Pairs of ambient and elevated CO2 octagons are distributed over the elevation gradient at the site and treated statistically as blocks within the experiment.
The CO2 concentration is enhanced by a Free Air Carbon Enrichment (FACE) system with a target concentration of 510 ppm. CO2 fumigation starts 30 min after sunrise and ends 30 min before sunset all year round, except during periods with full snow cover of the vegetation. The temperature enhancement is achieved by “passive night-time warming”, where a light scaffolding (0.5 m height) carrying a curtain reflects the outgoing infrared radiation. The curtains are automatically pulled over the vegetation at sunset and retracted at sunrise. In case of rain or heavy winds (> 7 m s-1) during the night the curtains are automatically withdrawn to avoid hydrological disturbance or damage to the curtains. The drought treatment is applied with water proof curtains automatically pulled over the vegetation during rain events to remove the water from the plots and are retracted when the rain stops. The automatic operation of the curtains according to day and night and climatic conditions is controlled by an astronomic watch, a rain sensor and a wind sensor.
Research activities and research ideas
At Brandbjerg the ongoing research focuses particularly on two issues:
- Multifactor manipulation of all three climate change factors: atmospheric CO2 concentrations, temperature and water availability.
- Changes in temporal variation patterns including extension of the growing season, increased frequency of freeze/thaw cycles, number of frost free days, frequency of extreme weather events etc.
The effects of the treatments on individual species, ecosystem structure and ecosystem functioning are investigated through targeted studies on the soil, plants, meso- and microfauna and microorganisms. The studies include changes in carbon and nutrient balances and circulation, stress tolerance and adaptation, species competition and composition and plant tissue chemistry and herbivory. The research take advantage of novel research tools including field scale ecosystem manipulations, stable isotope techniques, controlled herbivory and DNA techniques.
The on-site team
The INCREASE on-site team for Brandbjerg includes Klaus S. Larsen, Teis N. Mikkelsen, Dan Bruhn, Leon Linden, Claus Beier and Rikke Bagger Jørgensen.
For more information
Please, contact Klaus S. Larsen - email Risoe DTU, Technical University of Denmark, Risø National Laboratory for Sustainable Energy, P.O. Box 49, Frederiksborgvej 399, 4000 Roskilde, Denmark.
The Brandbjerg experiment is primarily funded by the Villum Kann Rasmussen Foundation and run by the “Climaite” project, which is a consortium of six research groups from the Technical University of Denmark, University of Copenhagen and the National Environmental Research Institute. Please, visit the website www.climaite.dk for more information.