Less pronounced drought responses in ring-porous than in diffuse-porous temperate tree species

Tree species differ in their physiological responses to drought, but the underlying causes are often unclear. Here we explored of radial growth centennial drought events and sap flow (Fs) seasonal four mixed forests on either moist or drier sites northwestern Switzerland. While diffuse-porous (Fagus sylvatica, Prunus avium, Tilia platyphyllos) showed marked reductions 1976 2003, two known marker years for severe ring-porous (Quercus petraea Fraxinus excelsior) was less severely affected. During a dry early midsummer, strongly reduced Fs at not (or so) moister sites. Regardless soil moisture availability, deep-rooting, trees invariably down-regulated 60–70% maxima response vapour pressure deficit (VPD) maintained similar fluxes across sites, irrespective upper conditions. A generalised additive model normalised as function VPD matric potential yielded drought-sensitivity ranking led by insensitive followed (ordered increasing sensitivity: excelsior < Quercus avium Acer pseudoplatanus Fagus sylvatica platyphyllos). In conclusion, tree exhibited stronger VPD-driven stomatal control over Fs, tree-ring formation sensitive than neighbouring species. The regulation explained greater tolerance trees.