Several coniferous tree species growing at the alpine timberline are known to show winter-embolism induced by drought and probably by freeze-thaw events. In the study presented, embolism in the coniferous shrub Pinus mugo growing above the alpine tree line was studied. We hypothesised adaptations in drought related vulnerability based on anatomical properties as well as the occurrence of refilling processes. During two winter seasons embolism rates were measured at different stands; vulnerability to drought induced embolism and xylem anatomy were analysed in twigs harvested at 600 m and at the timberline (1970 m). At the timberline, embolism rates of up to 30 % were observed in twigs above snow cover, whereas no conductivity losses were found in twigs below snow cover. Resistance to drought induced embolism was not increased at the timberline although tracheids as well as pits and pit pores were smaller than at 600 m. The lack of adaptation in vulnerability may be due to the restricted distribution of Pinus mugo. Refilling processes were observed not only in late winter but already in January. The conductivity losses in Pinus mugo prove winter-embolism to be a typical phenomenon in conifers at the alpine timberline - refilling processes may avoid impairments of the water transport system and be essential for plant water supply during the vegetation period.
