Nitrous oxide emission inventory of German forest soils

Annual fluxes of N2O trace gas emissions were assessed after stratifying German forest soils into Seasonal Emission Pattern (SEP) and Background Emission Pattern (BEP). Broad-leaved forests with soil pH(KCl) less than or equal to3.3 were assigned to have SEP, broad-leaved forests with soil pH( KCl) >3.3 and all needle-leaved forests to have BEP. BEPs were estimated by a relationship between annual N2O emissions and carbon content of the O-horizon. SEPs were primarily controlled by temperature and moisture and simulated by the model Expert-N after calibration to a 9-year record of N2O measurements. Analysis with different climate and soil properties indicated that the model reacts highly sensitive to changes in soil temperature, soil moisture, and soil texture. A geographic information system (ARC/INFO) was used for a spatial resolution of 1 km x 1 km grid where land cover, dominant soil units, and hygro climate classes were combined. The mean annual N2O emission flux from German forest soils was estimated as 0.32 kg ha(-1) yr(-1). Broad-leaved forests with SEP had the highest emissions (2.05 kg ha(-1) yr(-1)) followed by mixed forests (0.38 kg ha(-1) yr(-1)), broad-leaved forests (0.37 kg ha(-1) yr(-1)), and needle-leaved forests with BEP (0.17 kg ha(-1) yr(-1)). The annual N2O emission from German forest soils was calculated as 3.26 Gg N2O-N yr(-1). Although needle-leaved trees cover about 57% of the entire forest area in Germany, their contribution is low (0.96 Gg N2O-N yr(-1)). Broad-leaved forests cover about 22% of the forest area but have 55% higher emissions (1.49 Gg N2O-N yr(-1)) than needle-leaved. Mixed forests cover 21% of the area and contribute 0.81 Gg N2O-N yr(-1). Compared to the total N2O emissions in Germany of 170 Gg N yr(-1), forest soils contribute only 1.9%. However, there are some uncertainties in this emission inventory, which are intensely discussed.