There was a clear trend for trees with denser wood to
have proportionally thicker bark. The estimated of
genetic correlation between relative bark thickness and
pilodyn penetration in E. viminalis was strongly negative
(−0.75) at age 5 years. A similar finding was reported for
E. globulus (Dutkowski and Potts 1999; Lopez et al.
2002). The first authors suggested that this association
involved a pleiotropic relationship reflecting the joint
origin of wood and bark in the cambium. Interestingly,
this argument is not supported by the E. urophylla study
by Wei and Borralho (1997) where the estimated values
ranged from −0.20 to 0.14