Rapid growth in clonal Juglans nigra L. is most closely associated with early foliation, robust branch architecture, and protandry

Abstract The advantages of clonal forestry have been well described, but little progress has been made in the identification of phenotypes best suited to this method in high-value hardwood species. The genetic variation within, clonal repeatability (broad-sense heritability) of, and Pearson's correlations among phenological, morphological, physiological, and growth traits (N = 22) of black walnut (Juglans nigra L.) were investigated using 25 grafted clonal genotypes. The trees were grown at wide spacing (4.6 m × 6.1 m) in an intensively managed plantation in north-central Indiana, USA. Clonal effect was significant (p   0.70), including foliation dates, first female bloom, first pollen shed, and crown retention rate (autumnal defoliation). Some traits showed moderate repeatability (0.35