CO2 fluxes before and after partial deforestation of a spruce forest

Forest ecosystems are a sink for atmospheric CO2, but can weaken or turn into a source due to disturbances such as deforestation. Later, the recovering vegetation may be a weaker or stronger sink than the original forest. Changes in albedo additionally modify the total climate effect.We present seven years of flux measurements sampled above a spruce (picea abies) monoculture at the ICOS associate station candidate DE-RuW (50°30'N, 06°19'E, 600 m a.s.l.). The monoculture originally covered the whole headwater catchment (38.5 ha), which is highly instrumented in the framework of TERENO (TERrestrial ENvironmental Observatories). Three years after the start of measurements, 9 ha outside the main footprint of the tower were deforested to promote natural succession towards deciduous forest. A second eddy-covariance station was installed in the centre of the clearcut and soil respiration of both ecosystems measured manually at monthly intervals. Finally, we compared the climate effect due to changed CO2 sequestration with the biophysical one due to changed albedo.Annual sums of NEE measured above the forest showed a strong carbon sink with small inter-annual variability (-660±78 g C m-2 y-1). Over the four years since deforestation, the initially almost bare clearcut overgrew with grasses, shrubs and young deciduous trees (mostly rowan, sorbus aucuparia). The recovery is reflected by annual sums of NEE, which decreased from a carbon source of +521 g C m-2 y-1 towards almost neutral (+83 g C m-2 y-1). Soil respiration of the clearcut resembled the one of the forest floor during the first two years, but then became significantly higher during summer months as GPP increased. In terms of global radiative forcing, an immediate biophysical cooling effect of the deforested area, due to higher albedo of the soil and recovering vegetation, still overrides the cumulating biochemical effect of the missing CO2 sink