Here we show the usefulness of Long-Term Ecosystem Research (LTER) for scrutinizing climate change impacts on forest carbon (C) sequestration in the National Park Kalkalpen, Austria. Climate change will accelerate forest disturbances causing a decrease in forest C sink strength in the future. Delayed forest regeneration after stand replacing disturbances due to ungulate browsing opens an additional window for enhanced C loss. However, the dense grass layer, developing after large-scale disturbances, reduces ecosystem C loss by half, causing less climate feedback than expected. By applying two ecosystem models, we could show that wind and spruce bark beetle disturbances, which occurred during the last two decades throughout the National Park, increased soil organic C decomposition by 20% and will, together with future climate change, cause a 4% drop in forest ecosystem C stock by the year 2200. Keywords: ecosystem monitoring, LTER, climate change, carbon sequestration, modelling
