What are the effects of herbivore diversity on tundra ecosystems?

Northern ecosystems are strongly influenced by herbivores, but differences in diet composition, behaviour and energy requirements among herbivore species lead to contrasting impacts on ecosystem functioning. Arctic herbivore communities are changing rapidly in response to ongoing environmental and land use changes, and for these reasons, a better understanding of the consequences of changes in the diversity of herbivore assemblages in ecosystem functioning is needed. We used a systematic review to synthesize the available evidence on the effects of herbivore diversity on different processes, functions, and properties of Arctic tundra ecosystems. We searched primary field studies in databases, search engines and specialist websites and retrieved 5891 articles. After screening titles, abstracts, and full texts, 201 articles including 3955 studies were considered relevant for the systematic review. There was a geographical bias in the distribution of studies across the tundra biome, with most studies concentrated around well-established research locations. Most studies focused on the effects of a single herbivore species, while only a few studies specifically addressed the separate and combined effects of different herbivore species. The majority of studies focused on impacts of vertebrate herbivores on different aspects of arctic tundra vegetation, while other ecosystem processes, functions and properties have received less attention. Our results indicate that the available knowledge on the effects of herbivore diversity is relatively limited, so the consequences of ongoing changes in herbivore communities may be difficult to forecast. Future studies should explicitly address the role of herbivore diversity to understand the responses of tundra ecosystems to ongoing environmental changes.