20世纪后期气候加速变暖促进了北半球树木径向生长

20世纪后期全球加速变暖导致北半球森林衰退事件频发,并增加了树木生长-气候关系的复杂性。然而,关于气候加速变暖前后北半球不同地区树木生长对气候因子响应的异质性研究仍较为缺乏。本研究利用北半球3大洲9个地区共计229条温度敏感型树轮宽度年表分析了气候加速变暖前后不同地区树木生长趋势和气候响应的异质性表现。结果表明:(i)1977–2000年期间,气候加速变暖显著促进了北半球不同地区树木的径向生长,但在1950–2000年期间,不同地区的树木径向生长表现出异质性特征。(ii)1976年后,除北美中部和欧洲北部,北半球树木生长和温度的相关性均显著增加,亚洲地区最为明显。(iii)在1977–2000年期间,9个地区的树木年轮指数与温度均出现了短暂的分离(2–5年)。在1950–2000年期间,各地区树木生长能够更好地追踪到北半球平均温度的变化趋势而不是区域温度。

High-altitude tree growth responses to climate change across the Hindu Kush Himalaya

Aims Rapid warming at high altitudes may lead to a higher sensitivity in tree growth to temperature.The key factors constraining tree radial growth and to what extent regional tree growth has suffered from climatic changes are unclear.Methods Tree-ring width data were collected from 73 sites across the Hindu Kush Himalaya(HKH),including three dominant genera(Abies,Juniperus and Picea)at high altitudes over 3000 m.Dynamic time warping was introduced to develop subregional chronologies by considering the synchrony of annual tree growth among different sites.We quantified the contribution of the climate variables,and analyzed the spatiotemporal variation of the growth–climate relationship.Important Findings The site chronologies were grouped into three clusters,corresponding to the three distinct bioclimatic zones,i.e.the western HKH,central-eastern HKH and southeastern Tibetan Plateau(TP).Tree growth was positively correlated to winter and spring precipitation in the drier western HKH,and to winter temperature and spring precipitation in the humid southeastern TP.Tree growth was markedly constrained by the minimum temperature,especially in winter,with its importance increasing from the west toward the east.As shown by moving correlation analysis,the signal of winter temperature in tree growth was weakened in the western and central-eastern HKH,while it was enhanced in the southeastern TP following rapid warming since the 1980s.Our results highlight that continuous warming may cause forest recession due to warming-induced moisture deficit in the western HKH,but forest expansion in the southeastern TP.