By Isabel C. Barrio, Lead of the UArctic Thematic Network on Herbivory, Associate Professor, Agricultural University of Iceland and
David Hik, Professor, Simon Fraser University and
Bruce C. Forbes, Professor, University of Lapland and
Ingibjörg Svala Jónsdóttir, Professor, University of Iceland and
Elina Kaarlejärvi, Postdoctoral Researcher, University of Helsinki and
Mikhail V. Kozlov, Adjunct Professor, University of Turku and
Eeva M. Soininen, Researcher, UiT The Arctic University of Norway and
Henni Ylänne, Postdoctoral Researcher, Lund University and University of Eastern Finland and
Maria Väisänen, Postdoctoral Researcher, University of Oulu
Hundreds of species of plant-eating mammals, birds and insects – known as herbivores – inhabit the Arctic tundra. Some of these are vital for local communities and northern cultures, including domesticated reindeer and sheep, and hunted caribou, muskox, ptarmigan and geese.
Herbivores also contribute to the benefits that tundra ecosystems provide to people, the so-called ecosystem services. By feeding selectively on plants, trampling on plants and soils, and depositing urine and faeces, herbivores affect vegetation, biodiversity, productivity, energy flows, and nutrient cycling. In the case of reindeer and caribou, the impact on vegetation can be so significant that grazing differences along national borders or between different islands or pastures with different animal densities can be captured by satellite images.
The rapid climate warming in Arctic regions is affecting herbivores in many ways. Warming may lead to shortage of food during warmer winters when freezing rains lock vegetation under ice layers, or to increased food availability during longer and warmer summers. At a circumpolar scale, climate warming has triggered the expansion of trees and tall shrubs to and within tundra, but herbivores may also buffer this vegetation expansion in the treeless tundra. However, the impacts of herbivores and their effectiveness to counteract warming-induced changes in vegetation vary regionally and depend on many site-specific factors such as the type and abundance of herbivores.
The UArctic Thematic Network on Herbivory, with partners from nine UArctic member universities, explores the role of herbivory throughout the Arctic. Our initial studies assessed why some areas host a few herbivore species while others are home to diverse species assemblages. We found that herbivore diversity relates to plant productivity and the number of predatory species. If climate warming continues to increase productivity and the northward movement of boreal predators, diverse tundra herbivore assemblages may become more similar.
We have also quantified patterns of a neglected group of tundra herbivores, namely insects. Although insects consume little plant biomass in tundra (typically <1%), they are found nearly everywhere. In addition, insect herbivory increases with summer temperatures, suggesting that plant damage by insects as well as insect outbreaks will likely increase in a warmer Arctic.
Currently, we are synthesizing information about where and how the effects of herbivores on Arctic vegetation have been studied. This project will identify strengths and weaknesses in our current knowledge, which is relevant to local communities and their livelihoods (read more in the article on the CHARTER project, in which the Thematic Network is a partner). As rapid changes are occurring in the Arctic, we need a better understanding of the role of herbivory and its dependencies on site-specific factors to adjust management strategies and to preserve ecosystem services and biodiversity of diverse terrestrial Arctic environments. Coordinated herbivory research will allow for more robust predictions about the consequences of the rapid and ongoing changes in this region.