Silvopasture systems could be effective carbon sinks but their mitigation potential across geo-climatic gradients and management regimes remains understudied. To address this, we compared the simulated establishment of high-density hybrid walnut (Juglans regia x nigra) silvopasture across Europe over 30 years using DayCent with different scenarios and assumptions: regional-scale simulations with i) country-specific nitrogen (N) input rates, and ii) similar medium N input (∼100 kg N ha−1 yr−1), contrasted with iii) country-scale scenarios, co-designed with stakeholders (for the Netherlands, Switzerland, and Spain).
Simulated regional greenhouse gas (GHG) mitigation potential (from CO2 plus N2O) was largely driven by net primary productivity and N availability. Mitigation potentials of the similar N input rates scenario were around 1 t CO2-Ceq ha−1 yr−1 between 43 and 52° N latitude, up to 2 t CO2-Ceq ha−1 yr−1 in the most suitable area. For the high Belgian and Dutch N input rates (250-400 kg N ha−1 yr−1), the country-specific N input scenario suggested even higher mitigation potentials, but it is possible that this was an artifact of oversensitivity of DayCent to N, and requires further field investigation. The mitigation potentials at lower latitudes in both regional scenarios ranged from 0.7 t CO2-Ceq ha−1 yr−1 to no mitigation. Except for Switzerland, mitigation potentials of country-scale scenarios correlated strongly with those of regional simulations (R2 of 0.97 across all three countries; 0.88, 0.77, and 0.43 for the Netherlands, Spain and Switzerland, respectively), despite varying N input rates within the Netherlands and replacing walnut by Quercus ilex/suber trees in Spain. Thus, geo-climatic productivity constraints dominated the simulated GHG mitigation potential while management choices influenced the degree of its realization, especially in mountainous Switzerland.
