Leafy season length is reduced by a prolonged soil water deficit but not by repeated defoliation in beech trees (Fagus sylvatica L.): comparison of response among regional populations grown in a common garden

•Three years of soil water deficit delayed bud-burst and advanced leaf-yellowing.•Three years of annual experimental defoliations had no impact on leaf phenology.•Leafy season length varied among populations along a small latitudinal gradient.•Populations presented different leaf phenology response to soil water deficit.