Growth response of alpine treeline forests to a warmer and drier climate on the southeastern Tibetan Plateau

Forest growth at high altitudes and latitudes is sensitive to climate warming. However, warming-induced drought stress has decreased forest growth and survival rates, and constitutes a key uncertainty in projections of forest ecosystem dynamics. A fast warming rate has occurred over the Tibetan Plateau (TP), and the response pattern of alpine forest growth on the TP to a warmer and possibly drier climate is still unknown. By compiling tree-ring width records from ten alpine treeline ecotones (ATEs), we developed an index of regional tree growth in ATEs (RTGA) on the southeastern TP, which is a major forested region of the TP. Our results showed a stable and clear coherence between RTGA and the regional summer (June-August) minimum temperature during the studied period (1950-2012, R2 = 0.59, P < 0.001), despite a prominent drying trend since the 1990s. We conclude that warming-induced drought stress has not limited ATE forest growth on the moist southeastern TP.