Wildlife species benefitting from a greener Arctic are most sensitive to shrub cover at leading range edges

Abstract

Widespread expansion of shrubs is occurring across the Arctic. Shrub expansion will substantially alter arctic wildlife habitats. Identifying which wildlife species are most affected by shrubification is central to predicting future arctic community composition. Through meta-analysis, we synthesized the published evidence for effects of canopy-forming shrubs on birds and mammals in the Arctic and Subarctic. We examined variation in species behaviour, distribution and population dynamics in birds and mammals in response to shrub cover (including shrub cover indicators such as shrub occurrence, extent, density and height). We also assessed the degree of heterogeneity in wildlife responses to shrub cover and synthesized the remaining literature that did not fit the criteria for our quantitative meta-analyses. Species from higher green vegetation biomass habitats (high Normalized Difference Vegetation Index, NDVI, across their distribution) were more likely to respond positively to shrub cover, demonstrating the potential for species to expand from boreal to arctic habitats under shrubification. Wildlife populations located in the lowest vegetation biomass (low NDVI) areas of their species' range had the greatest proportion of positive responses to shrub cover, highlighting how increases in performance at leading edges of invaders distributions may be particularly rapid. This demonstrates the need to study species at these leading edges to accurately predict expansion potential. Arctic specialists were poorly represented across studies (limited to 5 bird and 0 mammal species), this knowledge gap potentially explains the few reported negative effects of shrub cover (3 of 29 species). Species responses to shrub cover showed substantial heterogeneity and varied among sites and years in all studies with sufficient replication to detect such variation.Our study highlights the importance of responses at species range edges in determining outcomes of shrubification for arctic birds and mammals and the need for greater examination of potential wildlife losers under shrubification. K E Y W O R D Sbirds, climate change, global warming, habitat suitability, herbivory, mammals, plant-animal interactions, shrub encroachment

Forecasted homogenization of high Arctic vegetation communities under climate change

“…A large‐scale increase in shrub cover may change the structure of tundra ecosystems by causing a reduction in the diversity of plant and animal species adapted to open tundra habitats. Increased shrub cover may, however, also be beneficial for some species and could therefore potentially lead to increased species diversity in some areas (Wheeler, Høye, & Svenning, ).…”

“…A large-scale increase in shrub cover may change the structure of tundra ecosystems by causing a reduction in the diversity of plant and animal species adapted to open tundra habitats. Increased shrub cover may, however, also be beneficial for some species and could therefore potentially lead to increased species diversity in some areas (Wheeler, Høye, & Svenning, 2018). warming through increased surface radiation associated with reductions in albedo due to darker and taller canopy covers (Myers-Smith et al, 2011) and an evapotranspiration-induced increase of the atmospheric moisture content (Bonfils et al, 2012).…”

Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome

“…Vegetation productivity is increasing in many regions of the Arctic, characterised by both northward distribution shifts and height growth of woody plants (Sturm et al 2001, Macias-Fauria et al 2012, Myers-Smith et al 2015. Increases in shrub cover and height will have important implications for vertebrate communities and herbivory in the Arctic (Wheeler et al 2017, Zhou et al 2017). Furthermore, northward range expansions of both boreal herbivores (e.g.…”

Anthropogenic impacts on the demographics of Arctic-breeding birds

“…Vegetation shifts in the Arctic occur when a warmer, wetter climate alters the structure of the vegetation communityfor example shrub encroachment or tree line advancement into the tundra (Wheeler et al 2018). Ground-nesting passerines often benefit from shifts towards increased vegetation cover, density and height (Henden et al 2013 andreviewed by Wheeler et al 2018).…”

“…Vegetation shifts at northern latitudes allow low-Arctic and boreal species to expand their range northwards, leading to an overall increase in bird abundance in the Arctic (Sokolov et al 2012;Wheeler et al 2018). Boelman et al (2015) predict that northward shrub encroachment will increase Z. leucophrys gambelii-a typical boreal speciesnesting habitat extent in Arctic Alaska.…”