The role of bryophytes for tree seedling responses to winter climate change: implications for the stress gradient hypothesis

1.When tree seedlings establish beyond the current tree line due to climate warming, they encounter existing vegetation, such as bryophytes that often dominate in arctic and alpine tundra. The stress gradient hypothesis (SGH) predicts that plant interactions in tundra become increasingly negative as climate warms and conditions become less harsh. However, for seedlings climate warming might not result in lower winter stress, if insulating snow cover is reduced.

2.We aimed to understand to if bryophytes facilitate seedling survival in a changing winter climate and if these effects of bryophytes on tree seedlings comply with the SGH along elevational gradients under contrasting snow conditions.

3.In the Swedish subarctic, we transplanted intact bryophyte cores covered by each of three bryophyte species and bryophyte-free control soil from above the tree line to two field common-garden sites, representing current and future tree line air temperature conditions (i.e. current tree line...