Red maple (Acer rubrum L.) stems (15–25 cm diam. at breast height) were wounded in the autumn or spring with horizontal, 1-cm wide chain-saw cuts 4 to 6 cm deep and 10 to 16 cm long. Wound occlusion (VO, vertical occlusion, at the wound side), bark dieback (BD, failure of horizontal occlusion above and below the wound), and the length of discoloured wood columns (DWC) were recorded after two growing seasons. For 93 trees (one wound each), correlations between lengths of BD and DWC were not significantly different above and below the wound (r= 0.58 and 0.56, respectively), with DWC being 2 to 3 times the length of BD. Corresponding correlations between the VO rating and the length of DWC were 0.41 and 0.38 (no significant difference). Compared with wounds made in the autumn, wounds made in spring caused less BD, greater VO, and shorter DWC. It is suggested that hydrostatic pressure in the wood, which is positive in the spring and negative in the autumn, is a major determinant of the volume of DWC and hence of wood that is susceptible to decay.