In the last decades, green alder (Alnus alnobetula (Ehrh.) K. Koch) has spread rapidly across the Alps. Once restricted to north-facing slopes, with high water availability, it is now expanding even into sites with impaired water availability. Observed leaf wilting following an extended drought period on a dry-mesic site at treeline, raised the question, whether the invasive species can adapt to dry conditions or if frequent drought events could limit the species’ expansion. To answer that question, we exposed three-year-old green alder saplings to two experimental drought phases and analyzed the effects on transpiration, photochemical yield and plant vigor. After 8 days of experimental drought transpiration of the plants had come to halt. Maximum photochemical yield (Fv/Fm) was not affected for 10 days, after which it rapidly declined to values near 0.1. After 15 days of drought more than 70 % of the leaves had wilted, but only 10 days after re-irrigation new leaves were sprouting, in the end replacing about 20% of the losses. Both transpiration and Fv/Fm recovered within seven days after re-irrigation, but transpiration values remained significantly below the control level for almost two months, indicating an adaptation or a legacy-effect of drought. Subsequent to the recovery to normal levels of transpiration, the plants were subjected to a second drought period. Drought stress continuously reduced transpiration, until it ceased 14 days after the onset of the drought. Fv/Fm was not affected for 12 days and afterwards did not fall to values lower than 0.7, indicating an adaptation to dry conditions. After 28 days of drought, most of the leaves had wilted and the experiment was terminated. A quarter of the plants measured showed no vital signs by early October, while the rest sprouted at least a few leaves despite the late season. Green alder has shown amazing resprouting vitality even after prolonged drought stress. However, in a warming climate, recurring drought events could delay or halt the spread of the species in exposed areas.