Fig. 2 Midday water potential (ψ_leaf) after two-month of drought treatment on 5 August 2018 (a, b), leaf net-photosynthesis (A_leaf) after two- (6 August 2018) (c, d) and four- (28 September 2018) (e, f) months of drought duration treatment in 2018, and the relative height increment (g, h) between 30 May (initial) and 1 October 2018 (after 4-months of drought treatment) for oak (Quercus petraea ) and beech (Fagus sylvatica ) saplings. D0 (watering weekly), D1 (watering biweekly), D2 (watering monthly), and D3 (watering bimonthly) represent the drought duration. Different letter indicates significant difference in parameters among D0, D1, D2, and D3.