Comparison of allometric model forms of heartwood ring number (HRN) against cambial age (CA) for diverse tree species. The models for Picea mariana, Picea abies, Pinus sylvestris, Pinus pinaster 1, Pinus pinaster 2, Larix decidua, Populus tremuloides are from Hazenberg and Yang (1991b), Longuetaud et al. (2006); Björklund (1999); Pinto et al. (2004); Knapic and Pereira (2005); Nawrot et al. (2008); Yang and Hazengerg (1991a), respectively, whereas the others are from this study.