How closely do ecosystem services and life cycle assessment frameworks concur when evaluating contrasting animal-production systems with ruminant or monogastric species?

Abstract

Life cycle assessment (LCA) and ecosystem services assessment (ESA) are often used for environmental assessment. LCA has been increasingly used over the past two decades to assess agri-food systems and has established that ruminant products have higher impacts per kg of protein than products from monogastric species. Conversely, ESA is used less but is likely to rank ruminant systems higher than monogastric systems, as the former often include grasslands that can provide high levels of regulating ecosystem services (ESs). Here, we applied both methods to a selection of contrasting meat-oriented animal-production systems that included either ruminants or monogastrics (6 of each). We considered 16 environmental impact categories in the LCA and two functional units: 1 kg of human-edible protein (HEP) and 1 m²yr of land occupied. We used the life-cycle inventory step of LCA to characterise the land occupation of the systems, i.e. the land cover types used, such as croplands and grasslands. Based on these land covers and quantification of the ES they provide, we performed ESA. We estimated that ruminant systems had higher environmental impacts than monogastric systems per kg of HEP for all 16 LCA impact categories studied. For example, for ruminants and monogastrics, mean greenhouse gas (GHG) emissions were 280 vs 32 kg CO₂-eq., respectively (P = 0.002), and mean fossil energy use was 351 vs 189 MJ, respectively (P = 0.009). The trend was the opposite for impacts per m²yr, with mean GHG emissions of 0.50 vs 0.57 kg CO₂-eq. (P = 0.485) and mean fossil energy use of 0.71 vs 3.63 MJ (P = 0.002) for ruminants and monogastrics, respectively. We also estimated that ruminant systems had a higher capacity to supply regulating ES than monogastric systems did, with mean scores of 2.4 and 1.2, respectively (P = 0.002), due to multiple types of grasslands in ruminant systems. Applying both LCA and ESA to a range of contrasting animal-production systems was a novelty of this study, and ESA indicated that ruminant systems have higher positive environmental contributions than monogastric systems. The study also found that LCA and ESA frameworks can agree or disagree on the assessments of animal-production systems depending on functional unit used (i.e. agreement per unit of land occupied but disagreement per unit of HEP).

Keywords: Cropland; Functional unit; Grassland; Land-cover profile; Trade-off.