Assessing the impacts of climate change on mountain ecosystems is challenging as it takes several decades to observe an ecological response. Using a transplantation experiment in the Swiss Jura Mountains we study the adaptability of beech and spruce to simulated climate change. In situ ecophysiological measures, e.g. photosynthetic rate at a constant CO2 partial pressure, were undertaken to assess the performance of saplings. Moreover, leaf phenology and growth rate monitoring were performed during the growing season. The main findings include a clear altitudinal effect on growth and photosynthetic capacity of both species and an advanced leaf flushing at lower altitudes.