Greenhouse gas fluxes (CO2, N2O and CH4) from forest soils in the Basque Country: Comparison of different tree species and growth stages

Abstract Forest systems are considered quintessential terrestrial systems for atmospheric CO 2 sequestration to mitigate the effect of global warming. Temperate forest soils also present the highest rates of methane uptake among all the natural systems, while may represent a significant source of N 2 O. Despite of the large area occupied by forest in the Basque Country, no data is yet available regarding greenhouse gas fluxes under these edaphoclimatic conditions. In this manuscript we present a 2-year study which determined the magnitude of CO 2 , N 2 O, and CH 4 soil gas fluxes in radiata pine, beech and Douglas fir forests using a closed chamber technique. The magnitude of these gas fluxes was additionally compared between different growth stages of radiata pine and beech forest, and the edaphoclimatic parameters that control these gas fluxes in the different forest systems and growth stages were studied. Measured greenhouse gas fluxes were in a low range as already published elsewhere for temperate forest ecosystems. A nitrogen deficit appears to be responsible for these relatively low gas fluxes. Apparently, the different forest species play a key role as controllers responsible for the differences of soil gas-exchange fluxes between the three different forest type systems. The mature pine plantation soil was emitting the most CO 2 (1.5 and 2.5 times more than the mature beech and the Douglas fir, respectively), while the Douglas fir forest soil was emitting the most N 2 O (3 and 17 times more than the mature pine and the mature beech, respectively) and the mature beech forest was the soil type showing the highest CH 4 consumption rates (2 and 5.5 times more than the mature pine and the Douglas fir, respectively). The stage of growth and its usual management appear to be important concerning the soil gas-exchange behavior within one forest type. The young beech forest soil emitted 9 times more N 2 O than the mature, and the new pine and the mature pine plantation soils emitted 2.5 and 2 times more CO 2 than the young, respectively. The ground vegetation cover percentage, the organic matter accumulation and the soil porosity seem to be factors which merit a closer look in future studies, as possibly responsible for the differences in gas fluxes among forest types and growth stages.