Divergent tree growth response to recent climate warming of Abies faxoniana at alpine treelines in east edge of Tibetan Plateau

An anomalous reduction in tree growth indices has been detected in tree ring records from many circumpolar northern latitude sites in recent years, which was known as the divergence phenomenon. In order to understand whether the divergence phenomenon appeared at altitudinal treelines in east edge of Tibetan Plateau, we analyzed the correlation coefficients between tree growth and climate variables before and after recent climate warming, respectively. The results showed that divergence phenomenon took place and varied with sites. Compared with those in 1955-1982, the correlation coefficient of growth to mean temperature in June declined during 1983-2012. In Songpan site, more than half of the sampled trees showed an increasing positive correlation with temperature from July to September, while others turned to be a negative correlation. The positive responses to the mean temperature in previous-year November and December declined in Markang site. Only in Miyaluo site, the positive correlation between tree ring index and temperature from July to September increased. Both the anomalous reduction or disappearance of the responses to the mean temperature and the divergent growth responses suggested that the divergence phenomenon was universal at altitudinal treelines in east edge of Tibetan Plateau, which had potentially significant influences on the estimation of forest productivity and climatic reconstructions based on tree ring.