Research on climate effects of large herbivores in Europe: a systematic map

Abstract

Abstract Background Land management practices have significant impacts on biodiversity and climate change processes. Conservation and rewilding practitioners are increasingly seeking to enhance ecosystem functions and carbon sequestration simultaneously, encouraged by climate policies such as the European Green Deal. In recent years, ecosystem restoration involving large herbivores (≥ 10 kg) has attracted growing interest. However, the climate impacts of large herbivores are complex, including direct and indirect impacts from greenhouse gas (GHG) emissions, carbon storage, wildfire and albedo. These impacts can have cooling or warming effects and vary with species, herd density, season and habitat. To date, the diverse research on this topic has not been collated and categorised in a systematic map. Here, we present a systematic map of research on the climate effects of large herbivores in European terrestrial habitats, highlighting research distribution, clusters and gaps, and the potential for further quantitative analyses. We address the primary question of what research exists on the climate effects of large herbivores in Europe. Methods Following our pre-published protocol, we used a pre-defined search string to conduct a search of peer-reviewed and grey literature, using a range of bibliographic databases, search engines and websites. We screened search results for relevance in two stages: by title and abstract, then full text. We excluded articles that failed to meet the eligibility criteria of terrestrial habitats in Europe (Population), large herbivores (Exposure) and climate impacts (Outcome). We coded the included studies by multiple variables, recorded in a spreadsheet alongside the narrative synthesis. Review findings We identified 316 articles for inclusion, involving a total of 565 studies (different research comparisons within the same article). Most studies were conducted in Northern Europe (63%), with the largest research cluster in the United Kingdom. Eastern Europe had the fewest studies (6%). The most frequently studied large herbivores were cattle (included in 54% of studies), sheep (34%) and reindeer (7%). Other types of large herbivores were included in fewer than 5% of studies (these included goats, equines, various species of wild cervids, European bison, pigs, wild boars, goat-antelopes (chamois), water buffaloes, beavers, and tortoises). The most frequently studied climate-related outcomes were soil carbon (included in 34% of studies), nitrous oxide (N 2 O) emissions (33%), carbon dioxide (CO 2 ) flux or emissions (21%) and enteric methane (CH 4 ) emissions (17%). Few studies combined multiple climate-related effects to estimate net emissions (6%). Conclusions The systematic map demonstrates substantial research gaps on the climate impacts of large herbivores. Research has predominantly focused on large domestic herbivores in agricultural contexts, particularly cattle and sheep. The research gaps for other large herbivores (and for natural and semi-natural habitats) present difficulties for conservation and rewilding practitioners in assessing the climate implications of their choices regarding large herbivores used in land management. The paucity of studies addressing net GHG emissions (accounting for multiple GHGs and carbon sequestration) also present challenges for determining which choices are likely to have net climate benefits. These research gaps have implications for policy and practice, particularly for nature-based carbon offsetting projects. Research to address these gaps would aid decision-making in both nature recovery and climate change mitigation.