Upward range shift of a dominant alpine shrub related to 50 years of snow cover change

Abstract

Pronounced climate warming has resulted in a significant reduction of snow cover extent, as well as poleward and upslope shifts of shrubs in Arctic and alpine ecosystems. However, it is difficult to establish links between changes in snow cover and shrub distribution changes due to a lack of in situ and long-term snow records in relation to abundance shifts of shrubs at their leading (i.e., cold) and trailing (i.e., warm) edges. We used remote sensing to extract long-term changes in both snow cover and shrub distributions in response to climate change in the alpine tundra of the Changbai Mountains in Northeast China. First, we analyzed spatio-temporal changes in snow cover during the snowmelt period (April 1st to June 15th) over the past 54 years (1965–2019). Then, we analyzed distribution changes of the dominant evergreen alpine shrub, Rhododendron aureum, using 31 years (1988–2019) of Landsat NDVI archives. We applied a novel approach by analyzing NDVI data from autumn only, when R. aureum is green yet most of the surrounding plants are already brown. Finally, we tested the relationship between snowmelt date and the distribution of R. aureum. We found that the fraction cover of R. aureum experienced greater loss than gain in the last 30 years. R. aureum expanded at the leading edge, establishing in snow-rich habitats, yet retracted further at the trailing edge due to loss of snow habitats. We identified the preferred snowmelt regime (habitats with snowmelt date of 20 April or later) of this shrub species and found that further advances in snowmelt dates would lead to the upward range shift of R. aureum in a warming climate. Our results indicate that spring snow cover change affected distribution changes of R. aureum. Our study highlights that long-term changes in snow cover due to climate change have already had marked impacts on plant species distributions in alpine ecosystems.