Drought in May inhibited conifer growth more seriously with climate warming in the southeastern Tibetan Plateau

Climate warming could benefit the tree growth of subalpine forests. However, increasing drought stress from climate change might limit tree growth and offset the beneficial effects in the cold and dry zone. In the past several decades, the southeastern Tibetan Plateau has experienced a rapid warming and enhanced aridification. How the conifer species have responded to climate change in this region remains unknown. We sampled seven conifer species at twelve sites with multiple elevations to reveal the growth response to climate change during 1961–2022 via dendroecological methods in the Muli Forest Region, southeastern Tibetan Plateau. The results showed that, except for Larix potaninii at both sites and Abies georgei at the 3620 m site, the growth of all other tree species/sites was significantly inhibited by the May drought, even at the alpine treeline. A rapid warming occurred after 1997, dividing the study period into two intervals, 1961–1996 and 1997–2022. Tree growth consistency across species/sites increased noticeably from 1997 to 2022. Radial growth of Picea likiangensis at the 3310 m site, Tsuga chinensis, and Pinus yunnanensis at the 2450 m site were limited by the May drought during the whole period, while Pinus armandii and Pinus densata have suffered the May drought since the 1990s. The growth of A. georgei at the 3320 m and the 4080 m sites, and P. likiangensis at the 3800 m site, was inhibited by the May drought after 2000. Overall, the inhibition of tree growth by May drought has been enhanced noticeably during 1997–2022, along with a higher consistency of tree growth. Given continued warming in the future, conifer tree growth may likely be further suppressed, which will decrease forest productivity in the southeastern Tibetan Plateau.