Jennifer Ramsay

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.

Background: In recent years there has been an increased focus on the role of large herbivores in ecosystem restoration and climate change mitigation. There are multiple processes by which large herbivores could potentially influence climate feedback and forcing effects, but the evidence has not yet been synthesised in a systematic and accessible format. Grazing, browsing, trampling, defecation, and seed dispersal by large herbivores can influence vegetation and soils in ways that may directly or indirectly contribute to climate change or mitigation. For example, changes in vegetation could impact wildfire regimes, carbon storage, and albedo, with ultimate impacts on climate. These processes may be influenced by herbivore species composition, density, and functional traits. The main aim of this systematic map is to synthesise the range of research on climate feedback and forcing effects from large herbivores (≥ 10 kg) in terrestrial ecosystems. We also aim to identify knowledge clusters and gaps in the research base, as well as assessing the potential for quantitative analyses. Methods: A search of peer-reviewed and grey literature will be conducted using a range of bibliographic databases, search engines and websites. The search strategy will involve using a pre-defined search string with Boolean operators. All search results will be screened for relevance according to specific eligibility criteria. Screening will be conducted in two stages: all articles will initially be screened by title and abstract, then those that meet the eligibility criteria will be screened by full text. At both stages, articles will be excluded if they don’t meet all eligibility criteria or if they meet any exclusion criteria. All articles included as eligible after full text screening will be coded. At each stage (of screening and coding) a proportion of articles will be processed independently by two reviewers to assess inter-reviewer reliability and resolve differences. The evidence will be presented in a searchable database with accompanying visual outputs. A narrative synthesis will be provided outlining the range and distribution of evidence, knowledge gaps and clusters, potential bias, and areas for further research.