A young afforestation area in Iceland was a moderate sink to CO₂ only a decade after scarification and establishment

Abstract. This study reports on three years (2004–2006) of measurements of net ecosystem exchange (NEE) over a young Siberian larch plantation in Iceland established on previously grazed heathland pasture that had been scarified prior to planting. The study evaluated the variation of NEE and its component fluxes, gross primary production (GPP) and ecosystem respiration (R_e), with the aim to clarify how climatic factors controlled the site's carbon balance. The young plantation acted as a relatively strong sink for CO₂ during all of the three years, with an annual net sequestration of −102, −154, and −67 g C m⁻² for 2004, 2005, and 2006, respectively. This variation was more related to variation in carbon efflux (R_e) than carbon uptake (GPP). The abiotic factors that showed the strongest correlation to R_e were air temperature during the growing season and soil water potential. The GPP mostly followed the seasonal pattern in irradiance, except in 2005, when the plantation experienced severe spring frost damage that set the GPP back to zero. It was not expected that the rather slow-growing Siberian larch plantation would be such a strong sink for atmospheric CO₂ only twelve years after site preparation and afforestation.