Radial growth of Qinghai spruce (Picea crassifolia Kom.) and its leading influencing climate factor varied along a moisture gradient

Understanding the spatial-temporal tree growth variability and its associative climatic response is fundamental in the assessment of forest vulnerability and the appraisal of forest risk under climate change. Based on 4219 tree-ring cores from 23 sample plots, this study demonstrates divergent radial growth dynamics of Qinghai spruce (Picea crassifolia Kom.) across a moisture gradient. On the one hand, contrary to the warming-induced growth enhancement of trees in cold regions reported in previous studies, our study find that Qinghai spruce growth has persistently declined under recent warming trends in multiple cold and moist sites that are representative of the Tibetan Plateau, China. On the other hand, Qinghai spruce growth exhibited W-shaped dynamic trajectories that were similar to changes in regional precipitation at all warmer and drier sites investigated in this study. Along with differences in regional evaporative change, differences in the growth-climate response can explain divergences in Qinghai spruce growth observed throughout various hydrological niches. Drought is believed to be the primary limiting factor of Qinghai spruce growth in all regions, resulting in a lower radial growth rate in warmer and drier regions. However, Qinghai spruce growth exhibited a higher dependency on the negatively-affected temperature in cold and moist regions, while the growth dependency respective to the positively-affected precipitation was higher than the temperature in warmer and drier regions. Results from this study are intended to add to the growing knowledgebase of forest response under persistent climate change.