C-fluxes and C-turnover of a mature mixed beech and pine stand under increasing temperature at ICP Integrated Monitoring site in Neuglobsow (Brandenburg)

Carbon fluxes and C-turnover of a mature mixed forest were assessed over a 5-year period from 2004 to 2008 at the Integrated Monitoring site “Neuglobsow”. The mature stand with European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) is located in the north-eastern German lowlands (Brandenburg). Soil carbon fluxes of the trenched and non-trenched plots were measured once a week with a closed chamber method to separate heterotrophic and autotrophic respiration. Annual wood increments were continuously measured by dendrometer bands. A strong correlation was found between observed and predicted soil respiration fluxes calculated on the basis of the measured soil temperatures and soil water contents. Carbon sequestration by accumulation in the aboveground biomass accounted for 1.67 Mg C ha−1 year−1. Including the C-sequestration in coarse roots the net primary production (NPP) increased to 2.0 Mg C per ha and year. Carbon release from soil by apparent heterotrophic respiration was overestimated due to higher soil moisture in the rootless trenching plots. Therefore we adjusted the apparent heterotrophic respiration by means of predicted water contents of the trenched plots, using a SVAT model. Accordingly the apparent heterotrophic respiration rate was 0.94 Mg C ha−1 year−1 resulting in a net ecosystem production (NEP) of 1.06 Mg C ha−1 year−1. The net C loss from the soil carbon pool may be caused by higher temperatures, which were increased by 1.5 °C during the observation period compared to the long-term temperature average (1961–1990). These short-term changes have to be regarded carefully interpreting measured carbon sequestration rates of forest ecosystems in the global carbon cycle.