Relative bark thickness: towards standardised measurement and analysis

Relative bark thickness (RBT; bark thickness/stem diameter; cm cm⁻¹) is a widely used species-specific plant trait, especially in the context of fire ecology. We consider several problems with its measurement and suggest that (1) it should be measured as bark thickness (BT)/bole diameter and not BT/stem diameter; (2) its measurement should be restricted to relatively small stems (<10 cm diameter); (3) ordinary least squares regression is sufficient for estimation of RBT and that this relationship should be forced through the origin so as to produce a slope and not an intercept, as well; and (4) associated life-history information, mainly whether taxa are epicormic resprouters, should be included in analyses. Finally, (5) we suggest that the relationship between allocation to new bark and retention of old bark is a crucial determinant of RBT.