Carbon footprint of transhumant sheep farms: accounting for natural baseline emissions in Mediterranean systems

Abstract Purpose Transhumance has rarely been analyzed through LCA approaches, and there is little evidence about its emissions level when conducted under different practices (by truck or on hoof), or compared to static/sedentary livestock systems. Moreover, mobile pastoralism is strongly linked to natural resources by its seasonal grazing patterns, thereby occupying the niche of wild herbivores. Considering natural emission baselines in these ecosystems could have relevant effects when estimating their carbon footprint. Materials and methods Inventory data of 21 sheep farms was collected in order to estimate the carbon footprint (CF) of lamb meat produced. Farms were divided in 3 sub-groups representing typical management practices in the region: i) static (STAT), ii) transhumance by truck (THT) and iii) transhumance on hoof (THH). Livestock GHG emissions were modelled according to herd structure and IPCC guidelines. Off-farm emissions from external feeds and fuels were accounted based on existent LCA databases. A natural baseline of wild herbivores was established from the population of red deer reported in a hunting preserve, previously considered to be a reference for the natural carrying capacity in Mediterranean ecosystems. GHG emissions of wild herbivores were estimated through two methods based on: i) IPCC guidelines, and ii) allometric regression equations. Results and discussion Carbon footprint ranged from 16.4 up to 30.6 kgCO2eq per kg of lamb liveweight (LW). Significant differences were identified among static and transhumant farms, which consistently showed lower CF values (STAT: 26.3 kgCO2eq/kg LW, THT: 18.1 kg CO2eq/kg LW, THH: 18.1 kg CO2eq/kg LW). Static farms resulted in higher GHG emissions (+31%) and higher CO2 and N2O, contributions derived from the consumption of additional feeds. Both methods applied to compute emissions for wild herbivores led to similar results (25.3-26.8 Mg CO2eq/km2), comparatively lower than estimation for transhumant sheep (47.7 Mg CO2eq/km2). When considering natural baseline emissions, the CF of transhumant lamb meat is reduced by almost 30%, reaching values quite below those reported for intensive lamb production systems in Spain. Conclusions From our results, mobility of grazing livestock can be considered as a strategy promoting climate change mitigation. This is achieved mainly by reducing the need of external feeds, while maximizing the use of local forage resources that otherwise would be difficult to valorize. Further reductions in the CF result when considering natural baseline emissions. The application of this new GHG accounting perspective could have relevant implications when aiming at climate neutrality of grazing-based ruminant systems.