Net Ecosystem Exchange (NEE) of the Island of Pianosa.

The overall gas exchange occurring between Mediterranean ecosystems and the atmosphere has been rarely quantified experimentally, butdue to the occurrence of prolonged summer drought that limits gas exchange, the potential carbon (C) sink of Mediterranean ecosystemsis generally considered low. Net Ecosystem C Exchange (NEE) was measured for a period of 12 months in the Island of Pianosa (CentralItaly) using the eddy covariance technique. The Island is partly covered by macchia vegetation and by abandoned agricultural land andit is ideal for flux measurements due to its flat topography and for the absence of anthropogenic C sources. C-flux measurements madebetween April 2002 and March 2003 showed that the Island of Pianosa was a net sink of C during a 12 months period accumulating 2.64t C ha-1 per year. Such a sink was less than what has been reported for evergreen forest in the region, but it is larger than what is generallyestimated for drought limited ecosystems. The analysis of seasonal changes in the C-flux revealed that phenology and temperature werelikely limiting C uptake during the winter months, while drought was limiting during the summer months. The potential C sink that couldbe provided by the entire island was finally calculated as the difference between the C stock contained at present in the Island's ecosystemsand that contained in the areas covered by the Mediterranean macchia.