CO2 fluxes of a Scots pine forest growing in the warm and dry southern upper Rhine plain, SW Germany

The effects of the warm and dry weather in the southern upper Rhine plain in the southwest of Germany on the carbon balance of the Scots pine forest at the permanent forest meteorological experimental site Hartheim were analysed over a 14-month period. The investigation of the net ecosystem exchange of carbon dioxide (F-NEE) of the Scots pine forest started in the extraordinary hot and dry August 2003. Carbon dioxide fluxes were measured continuously using an eddy covariance system and analysed by use of the EDDYSOFT software package. After determining the temperature dependence of the forest ecosystem respiration and the daytime light dependence of the CO2 exchange, monthly and annual carbon balances of the Scots pine forest were calculated. Mean peak daytime F-NEE rates observed 2 in August and September 2003 (-6.5 +/- 3.6 mu mol m(-2) s(-1)) were drastically lower than in August and September 2004 (-11.8 +/- 5.2 mu mol m(-2) s(-1)), which did not show pronounced deviations from the mean long-term (1978-2002) climatic conditions. In August 2003, the Hartheim Scots pine forest was a distinct CO2 source (35 g C m(-2)). The estimates of the annual carbon sink strength of the Scots pine forest ranged between -132 g C m(-2) (August 2003-July 2004) and -211 g C m(-2) (October 2003-September 2004). The main uncertainty in the determination of the carbon balance of the Hartheim Scots pine forest was introduced by the frequently low turbulence levels, i.e. the friction velocity corrected night-time F-NEE fluxes.