Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map
Authors: Soininen Eeva M. , Barrio Isabel C. , Bjørkås Ragnhild , Björnsdóttir Katrín , Ehrich Dorothee , Hopping Kelly , Kaarlejärvi Elina , Kolstad Anders Lorentzen , Abdulmanova Svetlana , Björk Robert G. , Bueno C. Guillermo , Eischeid Isabell , Higgens Rebecca Finger , Forbey Jennifer Sorensen , Gignac Charles , Gilg Olivier , den Herder Michael , Holm Hildur Søndergaard , Hwang Bernice C. , Jepsen Jane Uhd , Kamenova Stefaniya , Kater Ilona , Koltz Amanda M. , Kristensen Jeppe Aagaard , Little Chelsea J. , Macek Petr , Mathisen Karen Marie , Metcalfe Daniel , Mosbacher Jesper Bruun , Mörsdorf Martin Alfons , Park Taejin , Propster Jeffrey , Roberts Aradhana , Ferron Emmanuel Serrano , Spiegel Marcus P. , Tamayo Mariana , Tuomi Maria W. , Verma Megha , Vuorinen Katariina Elsa Maria , Väisänen Maria , Van der Wal René , Wilcots Megan , Yoccoz Nigel , Speed James D. M. 
Published: October 2021

Abstract
Background
Herbivores modify the structure and function of tundra ecosystems. Understanding their impacts is necessary to assess the responses of these ecosystems to ongoing environmental changes. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic. Strong spatial variation in herbivore effects implies that the results of individual studies on herbivory depend on local conditions, i.e., their ecological context. An important first step in assessing whether generalizable conclusions can be produced is to identify the existing studies and assess how well they cover the underlying environmental conditions across the Arctic. This systematic map aims to identify the ecological contexts in which herbivore impacts on vegetation have been studied in the Arctic. Specifically, the primary question of the systematic map was: “What evidence exists on the effects of herbivores on Arctic vegetation?”.

Methods
We used a published systematic map protocol to identify studies addressing the effects of herbivores on Arctic vegetation. We conducted searches for relevant literature in online databases, search engines and specialist websites. Literature was screened to identify eligible studies, defined as reporting primary data on herbivore impacts on Arctic plants and plant communities. We extracted information on variables that describe the ecological context of the studies, from the studies themselves and from geospatial data. We synthesized the findings narratively and created a Shiny App where the coded data are searchable and variables can be visually explored.

Review findings
We identified 309 relevant articles with 662 studies (representing different ecological contexts or datasets within the same article). These studies addressed vertebrate herbivory seven times more often than invertebrate herbivory. Geographically, the largest cluster of studies was in Northern Fennoscandia. Warmer and wetter parts of the Arctic had the largest representation, as did coastal areas and areas where the increase in temperature has been moderate. In contrast, studies spanned the full range of ecological context variables describing Arctic vertebrate herbivore diversity and human population density and impact.

Conclusions
The current evidence base might not be sufficient to understand the effects of herbivores on Arctic vegetation throughout the region, as we identified clear biases in the distribution of herbivore studies in the Arctic and a limited evidence base on invertebrate herbivory. In particular, the overrepresentation of studies in areas with moderate increases in temperature prevents robust generalizations about the effects of herbivores under different climatic scenarios.