Significance: Climatic warming is expected to shift alpine treelines upward because regeneration and growth of trees there are limited by low temperature. However, treeline displacement is spatially heterogeneous, despite warming climate. Using data on undisturbed spruce and fir treeline plots located on the Tibetan Plateau between 28.4 and 38.5°N, we showed that climatic warming tended to promote an upward shift of alpine treelines at local and regional scales. However, upslope migration rates were controlled largely by interspecific interactions. The species interaction mechanism both helps to explain why many treelines have not advanced in response to climatic warming and highlights that predictions of treeline shifts based solely on climate may be misleading, because interspecific interactions can temper effects of climatic change.