PRIMARY RESEARCH ARTICLE Long‐term changes in the impacts of global warming on leaf phenology of four temperate tree species Lei Chen 1* | Jian‐Guo Huang 1* | Qianqian Ma 1* | Heikki Hänninen 2* | Francine Tremblay 3 | Yves Bergeron 3 1 Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China 2 State Key Laboratory of Subtropical Silviculture, Zhejiang A&F University, Hangzhou, China 3 Forest Research Institute, Université du Québec en Abitibi‐Témiscamingue, Rouyn‐ Noranda, Quebec, Canada Correspondence Jian‐Guo Huang, Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China. Email: huangjg@scbg.ac.cn Funding information National Natural Science Foundation of China, Grant/Award Number: 100, Y421081001, GJHZ1752; Chinese Academy of Sciences Abstract Contrary to the generally advanced spring leaf unfolding under global warming, the effects of the climate warming on autumn leaf senescence are highly variable with advanced, delayed, and unchanged patterns being all reported. Using one million records of leaf phenology from four dominant temperate species in Europe, we investigated the temperature sensitivities of spring leaf unfolding and autumn leaf senescence (S T , advanced or delayed days per degree Celsius). The S T of spring phe- nology in all of the four examined species showed an increase and decrease during 1951–1980 and 1981–2013, respectively. The decrease in the S T during 1981–2013 appears to be caused by reduced accumulation of chilling units. As with spring phe- nology, the S T of leaf senescence of early successional and exotic species started to decline since 1980. In contrast, for late successional species, the S T of autumn senescence showed an increase for the entire study period from 1951 to 2013. Moreover, the impacts of rising temperature associated with global warming on spring leaf unfolding were stronger than those on autumn leaf senescence. The tim- ing of leaf senescence was positively correlated with the timing of leaf unfolding during 1951–1980. However, as climate warming continued, the differences in the responses between spring and autumn phenology gradually increased, so that the correlation was no more significant during 1981–2013. Our results further suggest that since 2000, due to the decreased temperature sensitivity of leaf unfolding the length of the growing season has not increased any more. These finding needs to be addressed in vegetation models used for assessing the effects of climate change. KEYWORDS chilling units, climate warming, early and late successional species, exotic species, phenology, photoperiod 1 | INTRODUCTION Plant phenology, the timing of periodic biological events in relation to climate fluctuations, has critical impacts on various aspects of ecosystem functions, such as carbon, water and nutrient cycling, tree fitness and distribution, and trophic interactions and structures (Richardson et al., 2013). Therefore, monitoring the timing of pheno- logical processes is important to the understanding of the impacts of global warming on terrestrial ecosystems (Cleland, Chuine, Menzel, Mooney, & Schwartz, 2007; Richardson et al., 2013). In recent decades, many studies have reported advanced spring phenological development of plants as a result of the climate * These authors contributed equally to this work. Received: 30 July 2018 | Accepted: 16 October 2018 DOI: 10.1111/gcb.14496 Glob Change Biol. 2018;1–8. wileyonlinelibrary.com/journal/gcb © 2018 John Wiley & Sons Ltd | 1