We investigated how tree- and forest lines (TFLs) in Norway have shifted over the past 50–130 years. Using remapped field observations, we show that the uppermost forest along the boreal-alpine ecotone is advancing at an average rate exceeding 0.5 m per year. This advance is driven by climate warming and land use. Our findings highlight the complexity and variation in TFL dynamics, caused by a combination of regional variation, stochastic disturbances, and time-lags.