Please cite this article as: Latte, N., Lebourgeois, F., Claessens, H.,Increased tree-growth synchronization of beech (Fagus sylvatica L.) in response to climate change in northwestern Europe, Dendrochronologia (2015), http://dx.doi.org/10.1016/j.dendro. 2015.01.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. responded to climate change, we selected 12 sites (137 trees) with optimal growing conditions 20 along a W−E altitudinal gradient (67-590 m) in Belgium. We evaluated temporal changes in 21 growth response to climate by using pointer year analysis, moving mean sensitivities (1860-22 2011), and moving bootstrapped correlation coefficients . The strongest driving 23 climatic variables were identified by using the partial least squares method. 24The common patterns of growth trends, pointer years, and mean sensitivities among sites 25 provided evidences for the impact of environmental changes operating at a regional scale. The 26 results of growth-climate analysis indicated that these changes were strongly influenced by 27 the climatic conditions of the previous year. The climate sensitivity of beech increased 28 progressively in response to more frequent and intense heat waves and warming-related 29 droughts, especially during recent decades, leading to remarkable inter-site synchronization. 30The changes were much more pronounced for sites located in lowlands (<300 m). The 31 differences in growth responses along the altitudinal gradient and the consequences of 32 warming for beech growth and physiology are discussed. 33