Can a bog drained for forestry be a stronger carbon sink than a natural bog forest?

This study compares the CO2 exchange of a natural bog forest, and of a bog drained for forestry in the pre-Alpine region of southern Germany. The sites are separated by only 10 km, they share the same soil formation history and are exposed to the same climate and weather conditions. In contrast, they differ in land use history: at the Schechenfilz site a natural bog-pine forest (Pinus mugo ssp. rotundata) grows on an undisturbed, about 5 m thick peat layer; at Mooseurach a planted spruce forest (Picea abies) grows on drained and degraded peat (3.4 m). The net ecosystem exchange of CO2 (NEE) at both sites has been investigated for 2 years (July 2010-June 2012), using the eddy covariance technique. Our results indicate that the drained, forested bog at Mooseurach is a much stronger carbon dioxide sink (-130 ± 31 and -300 ± 66 g C m-2 a-1 in the first and second year, respectively) than the natural bog forest at Schechenfilz (-53 ± 28 and -73 ± 38 g C m-2 a-1). The strong net CO2 uptake can be explained by the high gross primary productivity of the 44-year old spruces that over-compensates the two-times stronger ecosystem respiration at the drained site. The larger productivity of the spruces can be clearly attributed to the larger plant area index (PAI) of the spruce site. However, even though current flux measurements indicate strong CO2 uptake of the drained spruce forest, the site is a strong net CO2 source when the whole life-cycle since forest planting is considered. It is important to access this result in terms of the long-term biome balance. To do so, we used historical data to estimate the difference between carbon fixation by the spruces and the carbon loss from the peat due to drainage since forest planting. This rough estimate indicates a strong carbon release of +134 t C ha-1 within the last 44 years. Thus, the spruces would need to grow for another 100 years at about the current rate, to compensate the potential peat loss of the former years. In contrast, the natural bog-pine ecosystem has likely been a small but stable carbon sink for decades, which our results suggest is very robust regarding short-term changes of environmental factors

Can a bog drained for forestry be a stronger carbon sink than a natural bog forest?

This study compares the CO2 exchange of a natural bog forest, and of a bog drained for forestry in the pre-Alpine region of southern Germany. The sites are separated by only 10 km, they share the same soil formation history and are exposed to the same climate and weather conditions. In contrast, they differ in land use history: at the Schechenfilz site a natural bog-pine forest (Pinus mugo ssp. rotundata) grows on an undisturbed, about 5 m thick peat layer; at Mooseurach a planted spruce forest (Picea abies) grows on drained and degraded peat (3.4 m). The net ecosystem exchange of CO2 (NEE) at both sites has been investigated for 2 years (July 2010-June 2012), using the eddy covariance technique. Our results indicate that the drained, forested bog at Mooseurach is a much stronger carbon dioxide sink (-130 ± 31 and -300 ± 66 g C m-2 a-1 in the first and second year, respectively) than the natural bog forest at Schechenfilz (-53 ± 28 and -73 ± 38 g C m-2 a-1). The strong net CO2 uptake can be explained by the high gross primary productivity of the 44-year old spruces that over-compensates the two-times stronger ecosystem respiration at the drained site. The larger productivity of the spruces can be clearly attributed to the larger plant area index (PAI) of the spruce site. However, even though current flux measurements indicate strong CO2 uptake of the drained spruce forest, the site is a strong net CO2 source when the whole life-cycle since forest planting is considered. It is important to access this result in terms of the long-term biome balance. To do so, we used historical data to estimate the difference between carbon fixation by the spruces and the carbon loss from the peat due to drainage since forest planting. This rough estimate indicates a strong carbon release of +134 t C ha-1 within the last 44 years. Thus, the spruces would need to grow for another 100 years at about the current rate, to compensate the potential peat loss of the former years. In contrast, the natural bog-pine ecosystem has likely been a small but stable carbon sink for decades, which our results suggest is very robust regarding short-term changes of environmental factors

Effects of land use and climate on carbon and nitrogen pool partitioning in European mountain grasslands

European mountain grasslands are increasingly affected by land-use changes and climate, which have been suggested to exert important controls on grassland carbon (C) and nitrogen (N) pools. However, so far there has been no synthetic study on whether and how land-use changes and climate interactively affect the partitioning of these pools amongst the different grassland compartments. We analyzed the partitioning of C and N pools of 36 European mountain grasslands differing in land-use and climate with respect to above- and belowground phytomass, litter and topsoil (top 23 cm). We found that a reduction of management intensity and the abandonment of hay meadows and pastures increased above-ground phytomass, root mass and litter as well as their respective C and N pools, concurrently decreasing the fractional contribution of the topsoil to the total organic carbon pool. These changes were strongly driven by the cessation of cutting and grazing, a shift in plant functional groups and a related reduction in litter quality. Across all grasslands studied, variation in the impact of land management on the topsoil N pool and C/N-ratio were mainly explained by soil clay content combined with pH. Across the grasslands, below-ground phytomass as well as phytomass- and litter C concentrations were inversely related to the mean annual temperature; furthermore, C/N- ratios of phytomass and litter increased with decreasing mean annual precipitation. Within the topsoil compartment, C concentrations decreased from colder to warmer sites, and increased with increasing precipitation. Climate generally influenced effects of land use on C and N pools mainly through mean annual temperature and less through mean an- nual precipitation. We conclude that site-specific conditions need to be considered for understanding the effects of land use and of current and future climate changes on grassland C and N pools.Peer reviewe

Nitrous oxide emission budgets and land-use-driven hotspots for organic soils in Europe

Peer reviewe

Estimation of total, direct and diffuse PAR under clear skies in complex alpine terrain of the National Park Berchtesgaden, Germany

Information about total, direct and diffuse photosynthetically active radiation (PAR) is required in simulation models to estimate carbon gain and growth of vegetation. While there are existing worldwide networks of stations where direct, diffuse and reflected global radiation are measured using standardized methodology, no such network exists for PAR. In complex mountainous terrain, few published studies have examined even global radiation distribution as influenced by topography. We have developed a model to estimate the total, direct and diffuse photosynthetically active radiation in complex terrain. The model includes: (1) a parametric atmospheric model to extrapolate atmospheric conditions to any given location in complex terrain (which directly determines the potential PAR radiation that can be received on a horizontal surface) and (2) a topographic model, which accounts for the alteration of PAR radiation caused by terrain. Validation of the model was undertaken first for a baseline valley site at Schönau, an essentially flat surface with simple surrounding terrain. The hourly step atmospheric conditions were fit using direct PAR measurements at Schönau, and then applied in the parametric model to simulate the total and diffuse PAR. The results demonstrate that the parametric model provides good and fairly good simulations for total and diffuse PAR, respectively. In a second step, the model was tested for total PAR at five sites with distinctive topographic characteristics in the National Park Berchtesgaden, Germany, and for direct and diffuse radiation at two of the five sites with direct and diffuse PAR measurements. The model simulated total PAR well with high R2 (all >0.90). The NRMSE varies from 8% to 26% depending on sites. Although high R2 were found for direct PAR at the two sites Kederbichl and Bartholomä (both 0.92), lower R2 of 0.64 and 0.65 were obtained for the diffuse PAR simulation. While the NRMSE for diffuse PAR was also lower (0.23 for Kederbichl site and 0.26 for Bartholomä site), this difference was not as pronounced (0.31 for Kederbichl site and 0.28 for Bartholomä site for direct PAR). The R2 decreases to 0.14 and 0.33 for the two sites in the diffuse PAR simulation, if the diffuse PAR is treated isotropically. Thus, the results suggest that consideration of anisotropic distribution of diffuse radiation is required in PAR extrapolation models within complex alpine terrain

Soil-atmosphere greenhouse gas exchange in a cool, temperate Eucalyptus delegatensis forest in south-eastern Australia

Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH₄) sink, whilst producing little nitrous oxide (N₂O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil-atmosphere N₂O, CH₄ and CO₂ exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N₂-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO₂ exchange. CH₄ was taken up by the forest soil (-51.8μg CH₄-Cm⁻² h⁻¹) and was significantly correlated with relative saturation (S r) of the soil. The soil within creek lines was a net CH₄ source (up to 33.5μg CH₄-Cm⁻² h⁻¹), whereas the wider forest soil was a CH₄ sink regardless of distance from the creek line. Soil N₂O emissions were small (20. Soil-atmosphere exchange of CO₂ was several orders of magnitude greater (88.8mg CO₂-Cm⁻² h⁻¹) than CH₄ and N₂O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22kg CO₂-equivalents ha⁻¹ d⁻¹) during the 2-week measurement period, of which soil CH₄ uptake contributed only 0.3% and N₂O emissions offset only 0.3%