The greenhouse gas balance of European grasslands

Abstract

The long-term carbon balance (NBP) of grasslands is estimated by combining scarce multi-year eddy-covariance observations at ecosystem observation sites where information on carbon inputs and harvesting removals is available. Following accounting for carbon leached to rivers, we estimated grasslands to be net carbon sinks of 74±10 g C m<sup>−2</sup> yr<sup>−1</sup>. Uncertainties arise from the small number of sites and the short measurement period. Only 11 sites, out of a total of 20 grassland sites in Europe where eddy covariance systems are installed, were set-up for estimating NBP. These 11 selected sites are representative of intensive management practice and we lack information on disturbance history, such as plowing. This suggests that the grassland NBP estimate is likely biased towards overestimating the sink, compared to the European average. Direct measurements of Net Primary Productivity (NPP) are not possible in grasslands given permanent biomass removal by grazing and mowing, uncertainties in rhizodeposition and production of volatile organic carbon compounds lost to the atmosphere. Therefore, the grassland process-based ecosystem model PASIM was used to estimate the spatial-temporal distribution of NPP, providing a European average value of 750±150 g C across extensively grazed, intensively grazed pastures, and forage production systems. In Europe the NPP of grasslands seems higher than that of croplands and forests. The carbon sequestration efficiency of grasslands, defined as the ratio of NBP to NPP, amounts to 0.09±0.10. Therefore, per unit of carbon input, grasslands sequester 3–4 times more carbon in the soil than forests do, making them a good candidate for managing onsite carbon sinks. When using the 100 yr greenhouse warming potential for CH<sub>4</sub> and N<sub>2</sub>O, their emissions due to management of grasslands together offset roughly 70–80% of the carbon sink. Uncertainties on the European grassland greenhouse gas balance, including CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O fluxes are likely to be reduced in the near future, with data being collected from more sites, and improved up-scaling methods

Linking biomass production in short rotation coppice with soil protection and nature conservation

“…The main concerns here were a distinct loss of soil organic carbon, leaching of nitrate into the groundwater, and the release of carbon dioxide into the atmosphere due to increased mineralization following conversion from grassland to SRC (Don et al 2009, Ciais et al 2010. However, a land use change from grassland to SRC does not necessarily imply high losses of soil organic carbon (Don et al 2012).…”

Carbon storage of Mediterranean grasslands

“…The Earth's grasslands, including tropical savannas, represent approximately 20% of the total terrestrial biomass (Scurlock & Hall, 1998;Robinson, 2007) and contain in their soils at least 28% of the global stock of carbon (Robinson, 2007) and 12% of the soil organic matter (SOM; Jones, 2010). Even in the European Community in general, and in Italy in particular, grasslands are an important terrestrial carbon pool and, although they may be sources of greenhouse gases (e.g., methane and nitrogen oxides), they generally represent a net carbon sink as important as that of forest ecosystems (Janssens & al., 2005;Gilmanov & al., 2007;Ciais & al., 2010).…”

“…Ciais & al., 2010). The FAO (2006), however, reported a reduction of almost 13% of the European grassland covering between 1990 and 2003.…”

“…Grasslands also play an important role in the global carbon cycle (Parton & al., 1995), particularly as a consequence of carbon sequestration in soil (Ciais & al., 2010). The carbon stored in grassland soils represents a rather stable carbon pool (Hungate & al., 1997).…”

Prerequisites for application of hyperbolic relaxed eddy accumulation on managed grasslands and alternative net ecosystem exchange flux partitioning

“…European grassland ecosystems are still to be defined as a net carbon sink or source. For this reason, detailed investigation is greatly required (Ciais et al, 2010;Soussana and Lüscher, 2007). In addition to the general uncertainty regarding the sink/source behavior of grasslands, management of grassland ecosystems causes anomalies in the seasonal carbon cycle (Flechard et al, 2005).…”