Snow is a critically important and rapidly changing feature of the Arctic. However, snow-cover and snowpack conditions change through time pose challenges for measuring and prediction of snow. Plausible scenarios of how Arctic snow cover will respond to changing Arctic climate are important for impact assessments and adaptation strategies. Although much progress has been made in understanding and predicting snow-cover changes and their multiple consequences, many uncertainties remain. In this paper, we review advances in snow monitoring and modelling, and the impact of snow changes on ecosystems and society in Arctic regions. Interdisciplinary activities are required to resolve the current limitations on measuring and modelling snow characteristics through the cold season and at different spatial scales to assure human well-being, economic stability, and improve the ability to predict manage and adapt to natural hazards in the Arctic region.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-016-0770-0) contains supplementary material, which is available to authorized users.

invertebrate herbivory on dwarf birch (Betula glandulosa-nana 1 complex) increases with temperature and precipitation across the tundra biome ' Polar biology, vol. 40, no. 11, pp. 2265-2278. DOI: 10.1007%2Fs00300-017-2139 Digital Object Identifier (DOI): 10.1007%2Fs00300-017-2139-7 Link: Link to publication record in Edinburgh Research Explorer Document Version: Peer reviewed version Published In: Polar biology General rightsCopyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policyThe University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact openaccess@ed.ac.uk providing details, and we will remove access to the work immediately and investigate your claim. Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, 78 yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to 79 predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the 80 intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), 81 and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, 82 mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our 83 results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low 84 intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The 85 damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% 86 leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a 87 lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on 88 average, foliar losses to invertebrates on dwarf birch are likely to increase by 6-7% over the current levels with a 1 89 °C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in 90 magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory 91 should be included in predictions of climate change impacts on tundra ecosystems. 92 3

1In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change 2 with the availability of that habitat, resulting in a functional response in habitat use. Here we investigate the 3 relationship of two specialized herbivores, willow ptarmigan (Lagopus lagopus) and mountain hare (Lepus 4 timidus), to willows (Salix sp) in three regions of the shrub tundra zone -northern Norway, northern 5 European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets 6 represent a major structural element and are important for herbivores both as food and shelter. Using faeces 7 counts in a hierarchical spatial design and several measures of willow thicket configuration we document a 8 functional response in the use of willow thickets by ptarmigan, but not by hare. For hares, whose range 9 extends into forested regions, occurrence increased overall with willow cover. For willow ptarmigan, 10 occurrence showed a strong positive relationship to willow cover and a negative relationship to thicket 11 fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be 12 limited by reindeer browsing. In regions with higher cover, on the contrary, such relationships were not Introduction 21The availability of suitable habitats determines the distribution of animals at different 22 scales (Johnson 1980; Mayor et al. 2009; Orians and Wittenberger 1991). As animals 23 select their habitat in function of their needs for all activities required for successful 24 reproduction and survival, the optimal habitat is in fact often composed of a mixture of 25 patches of several habitat types (Orians and Wittenberger 1991). Different habitats may for 26 example be optimal for foraging and for shelter or breeding, resulting in trade-off 27 situations (e.g. Mysterud et al. 1999). Habitat and landscape selection can in such cases 28 vary in space in relation to changes in availability of important landscape elements (Fortin 29 et al. 2008). A positive relationship between animal abundance and cover of a particular 30 habitat may for instance be restricted to a certain range of cover values and flatten out or 31 even decrease at higher values, meaning that the preference for a given type of habitat may 32 change with its availability. Such a relationship has been defined as a functional response 33 in habitat use by Mysterud and Ims (1998) habitat. Willows (Salix sp.) usually grow along rivers or on slopes and are often the tallest 42 plants in the tundra landscape, which is otherwise characterized by low-statured plants 43 (Pajunen 2009; Pajunen et al. 2010). The thickets represent a major structural element and 44 are highly productive habitats compared to the surrounding open tundra vegetation. They 45 (den Herder et al. 2004(den Herder et al. , 2008 47 Ims et al. 2007; Henden et al. 2010). Under global change, the growth of shrubs is 48 increasing in the tundra, and shrubs are expanding northwards (Sturm et al. 2001; Ta...