Spatial heterogeneity of ecosystem carbon fluxes in a broadleaved forest in Northern Germany

Carbon fluxes were investigated in a mature deciduous forest, located in Northern Germany (53degrees47'N-10degrees36'E), by means of eddy-covariance technique, stand survey and models. This forest has been managed following a concept of nature-oriented forestry since the 1980s. One of the goals of the study was to test whether changed management led to increased carbon sequestration. The forest contains several broadleaved tree species. Depending on wind direction, the fetch-area of the eddy-covariance data was dominated by different tree species. Three subplots dominated by Oak, Beech or Alder/Ash could be distinguished from the tower data. In each of these subplots, 30 x 30 m(2) areas were defined to analyse leaf area index, litterfall and the increase of the wood biomass. Eddy-covariance analysis showed that the gross primary productivity (GPP') was higher in the Oak subplot (-1794 g C m(-2) yr(-1)) in comparison with the Beech plot and the Alder/Ash plot (-1470 and -1595 g C m(-2) yr(-1), respectively). The total ecosystem respiration (TER) was the highest in the Alder/Ash-dominated subplot (1401 g C m(-2) yr(-1)) followed by the Oak plot and the Beech plot (1235 and 1174 g C m(-2) yr(-1), respectively). The resulting net ecosystem productivity (NEP) was -559 g C m(-2) yr(-1) for the Oak-dominated subplot, -295 g C m(-2) yr(-1) for the Beech plot and -193 g C m(-2) yr(-1) for the Alder/Ash plot. From Stand survey and modelling, the net primary productivity was estimated as 1103, 702 and 671 g C m(-2) yr(-1) in the Oak, Beech and Alder/Ash plot, respectively. Also carbon flux with litterfall was the highest in the Oak plot 343 g C m(-2) yr(-1) and lowest in Alder/Ash plot (197 g m(-2) yr(-1)) with the Beech plot in between (228 g m(-2) yr(-1)). The observations indicate an increase of the proportion of litterfall with increasing GPP' and a different ability of carbon sequestration of the three stands in medium temporary scale. Only in the Oak stand that comprised the oldest trees and the most structured canopy the carbon sequestration was increased compared with conventionally managed forests.