Annual changes in wood characteristics in EW (circles) and LW (triangles) of control (closed symbols) and stressed oaks (open symbols) since 2003. NV, MVA, TVA and CA denote number of vessels, mean vessel area, total vessel area and conduit area, respectively. Means and standard errors of at least four trees per treatment are shown as a percentage of the starting situation (control) in 2003. Asterisks indicate significant differences between stress and corresponding control values (p ≤ 0.05).