Reduced snow cover affects productivity of upland temperate grasslands

- Annual gross ecosystem production and respiration correlated with elevation.
- Timing and volume of snow cover affected the annual carbon balance.
- Without snow cover, carbon uptake was controlled by (soil) temperature.
- Foehn frequency represents a regional climate signal for ecosystem processes.

The 2013/2014 winter season showed exceptionally sparse snow cover conditions north of the Alps, which allowed an in situ investigation of the response of vegetation to changed environmental conditions. Examination of carbon dioxide fluxes at three grassland sites along an elevation gradient from 595 to 864 m a.m.s.l. revealed that elevation, snow cover extent, soil temperature (Tsoil) and management were determinative factors for productivity. In the absence of snow cover at the highest elevation site (864 m), substantial growth started only when the mean daily Tsoil exceeded 5 °C. The lack of snow cover at the lowest elevation site (595 m) allowed the vegetation to remain photosynthetically active throughout the winter, with a canopy that developed after the last harvest of the previous season. The reduced snow cover at the lower elevation sites (595 and 769 m) resulted in an earlier spring, a significant increase in gross ecosystem production and ecosystem respiration, as well as enhanced seasonal carbon dioxide uptake. The reduced snow cover in the 2013/2014 winter season is attributed to low precipitation and high energy influx, which in turn were best explained by exceptionally frequent foehn, i.e., southern advection of dry, warm air across the Alps.