The University of Giessen Free-Air Carbon Dioxide Enrichment Study (GiFACE)
The University of Giessen long-term Free-Air Carbon Dioxide Enrichment experiment started in 1998 to study responses of a semi-natural grassland (cf. site description) to elevated CO2.
For the prediction of long-term effects of increasing CO2 concentrations on different compartments and sub-compartments of a semi-natural grassland ecosystem a new free-air CO2 enrichment technology was developed during 1994-1996.
In 1997, six of 16 previously monitored 100 m2 plots were selected for three ring pairs and the CO2 treatment was randomly assigned to one of the rings within each block. The blocks cover a slight soil moisture gradient caused by different depths of a clay layer as well as from the average ground water table. However, even if the rings pairs are reffered to as 'dry', 'wet' or 'intermediate' in moisture, the ring plots are covered with the same type of vegetation.
The installation of the FACE and control rings was carried out in 1997, the CO2 enrichment started May 1998. The CO2 enrichment is performed year-round during daylight hours (2 hours after sunrise - 2 hours before sunset) to +20 % ambient conditions.
The GiFACE is currently the oldest running long-term FACE experiment on a semi-natural grassland ecosystem in Europe. The project operating time is 15-20 years.