GENETIC AND INTRA-TREE VARIATION IN THE NUMBER OF SAPWOOD RINGS IN QUERCUS-ROBUR AND Q-PETRAEA

This study investigates genetic control of the number of sapwood rings in Quercus robur and Q. petraea, and the variation of this trail with height up the stem and age oi the tree. Ramets and open-pollinated pr ogeny af the 2 species were sampled from a German clonal orchard and a n unreplicated progeny trial; intra-tree variation was investigated fr om a sample of English woodland trees of both species. Estimates of th e heritability of the number of sapwood rings were high (0.57 +/- 0.28 on a narrow-sense basis; 0.83 +/- 0.11 on a broad-sense, clonal mean basis), consistent with comparable results for other species. The phen otypic correlation between family means, used here as the best availab le proxy to a genetic correlation, suggested a moderately negative rel ationship (r = -0.49) in trees of the same age between the number sf s apwood rings and stem diameter at breast height. The number of sapwood rings and the proportion of rings that are sapwood varied with height , following a nonlinear relationship. The number of sapwood rings at b reast height increases with the age of the tree, although the proporti on of the total number of rings that are sapwood decreases with age. W hilst strong conclusions cannot be drawn from the limited experimental material on which this study is based, our results are generally cons istent with those of other studies. They suggest that including the nu mber of sapwood rings as a selection criterion could be beneficial in both breeding and clonal propagation programmes of Q. robur and Q. pet raea.