Arctic shrub expansion: drivers of growth and effects on litter decomposition
Tall deciduous shrubs are expanding into graminoid-dominated Arctic tundra due to warming. Shrub expansion is expected to alter the structure and functioning of tundra ecosystems in ways that could feedback to global climate. However, the determinants of shrub growth and the effects of shrubs on litter decomposition at different scales remain poorly resolved. I addressed these knowledge gaps by evaluating the drivers of shrub growth and litter decomposition across five sites spanning a 160 km latitudinal gradient in northern Alaska. Using dendroecological analyses, I found that both regional climate and individual-level plant traits influence shrub growth. I also found that litter quality was the predominant control on shrub litter decomposition, whereas regional climate and microclimate controlled the litter decomposition of a dominant sedge species. Overall, these results demonstrate that both fine-scale drivers and traits influence shrub-related responses to warming and can improve our ability to accurately model changing Arctic ecosystems.