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.

Drained lake basins (DLBs) are dominant features in lowland permafrost landscapes of the Arctic. Here, we present a novel approach describing and quantifying the succession progression of recently drained basins using a land cover unit retrieval scheme developed specifically for the Arctic tundra biome. The complementarity between land cover units and Normalized Difference Vegetation Index (NDVI) analyses is shown. Land cover units were linked to DLB ages (years passed since a drainage event occurred). The data were divided into bioclimate subzones, and the land cover units were grouped according to their characteristics, first related to vegetation and second to wetness gradients (dry, moist and wet). Regression analyses of NDVI values and fraction of each land cover unit group provided the justification for the utility of the units in our research. The regression results showed the highest correlation with NDVI values for the wetness group “Moist” and the vegetation group “Shrub Tundra” (R²=0.458 and R²=0.444). There was no correlation (R²=0.066) between NDVI and the fraction of the “Wet” group. The inconsistency in the association between those variables underlines the need to complement NDVI analyses with a scheme representing wetness, such as the use of land cover units to describe changes in wetland areas. Finally, our results showed different trajectories in the succession of land cover units in recently drained lake basins with respect to different bioclimate subzones. Remaining water in the basin after a lake drainage event was highest for the most southern subzone (median 6.28 %). The open water fraction dropped below 1 % for all subzones after 5 to 10 years since drainage. The results of this study contribute to an improved understanding of DLB land cover change in permafrost environments and to a better knowledge base of these unique and critically important landforms.

Mycorrhizal fungi play an integral role in nutrient and carbon cycling in soils, which may be especially important in the Arctic, one of the world's most soil carbon‐rich regions. Large mammalian herbivores can influence these fungi through their impacts on vegetation and soil conditions, however the strength and prevalence of these interactions in the Arctic is still uncertain. We collected soils from 15 large mammal exclusion experiments across the Arctic. We sequenced both ITS regions and partial SSU regions using two sets of amplicons to determine the composition of soil mycorrhizal fungal communities. This allowed us to assess how these communities are impacted by exclusion of large mammalian herbivores, plant communities, and climate and soil properties. Large mammalian herbivore exclusion had a significant impact on the arbuscular mycorrhizal (AM) community dissimilarity between sites. The AM community was also influenced by growing season temperature and pH, which may indicate that conditions are becoming more favourable for these species in some Arctic communities. Large herbivore exclusion did not have a coherent impact on ectomycorrhizal and ericoid mycorrhizal fungal community dissimilarity, which were primarily correlated with δ ¹⁵ N signature in the soil, rather than herbivory, climate, or plant functional types. The consistent detection of arbuscular mycorrhizal fungi identified highlights the need for more thorough evaluations of these communities and their role in Arctic carbon and nutrient dynamics, as these fungi are currently understudied in the Arctic.