The Role of Grasslands in a Green Future 147 The value of silvopastoral systems in the mitigation of greenhouses gas emissions: A case study from NW Spain Mosquera-Losada M.R. 1 , Rigueiro-Rodríguez A. 1 and Fernández-Núñez E. 2 1 Crop Production Department, Escuela Politécnica Superior, Campus de Lugo, University of Santiago de Compostela, Spain 2 Mountain Research Centre (CIMO), IPB, 5300 Bragança, Portugal Corresponding author: mrosa.mosquera.losada@usc.es Abstract Carbon sequestration is promoted as a practice to offset the negative consequences of greenhouse gas emissions. The aim of this study was to estimate carbon sequestration in silvopastoral systems established with Pinus radiata D. Don and Betula pubescens Ehrh. The soil compartment proved the most significant carbon sink, and carbon sequestration tended to be higher under P. radiata due to the higher growth rate of this species compared to B. pubescens. Keywords: livestock, Monterey pine, Downy birch, carbon sequestration, silvopasture Introduction The European Union has agreed to reduce its greenhouse gas emissions (GHG) by 20% by 2020, from base-year levels (1990) (EEA, 2011). Silvopastoral systems (SPS), when compared to systems that are exclusively agricultural, can contribute to the mitigation of climate change by acting, to a greater degree, as sinks for GHG. In this type of systems, tree species and an adequate management of the pasture carrying capacity (PCC) will contribute to increased carbon sequestration. Carbon storage in a SPS is counterbalanced by the emissions of GHG (CH 4 and N 2 O) produced by the ruminants that feed on it. The quantity of GHG emitted by livestock depends on the stocking rate, which depends on the pasture production and which is affected by tree development after afforestation. The objective of this study was to estimate the C balance in two SPS established with Pinus radiata and Betula pubescens for the 11-year period that elapsed since the planting of the trees. Materials and methods The experiment was conducted in Lugo (NW Spain) at 439 m a.s.l. The experimental design was established using randomized blocks with three replicates. Two forest species were planted (25 trees per plot): Pinus radiata D. Don (Monterrey pine: pine) and Betula pubescens Ehrh. (Downy birch: birch) at 833 trees ha -1 . In 1995 the plots were sown with Dactylis glomerata L. and clovers (Trifolium repens L and Trifolium pratense L.). Plots were fertilized with dairy sludge in 1995 at 154 m 3 ha -1 . In 1996 and 1997, the plots were not fertilized, but fertilization ensued in 1998 and continued to 2005 at levels of 500 kg ha -1 of 8:24:16 (N: P 2 O 5 : K 2 O) in March, and 40 kg of N ha -1 in May. To compare the C balance of the system (Figure 1), three main components were considered: Tree, Soil and Pasture (including livestock losses). Tree: Diameter at breast height (DBH) measurements was taken in 2005 from the inner nine trees, to eliminate border effects. Based on DBH, tree biomass (trunk, fine and thick branches, leaves and roots) was calculated via allometric equations determined by Montero et al. (2005).