Abstract

Short-rotation coppice (SRC) using hybrid poplars for biomass production may be a productive alternative in Mediterranean zones. However, the degree of genetic control and the growth stability of poplar clones in high-density plantations remain unknown, and information is needed to reduce the selection time in SRC systems. The genetic variation and stability of growth traits with the age of hybrid clones (from interspecific crosses of Populus deltoides [D], P. trichocarpa [T], P. nigra [N] and P. maximowiczii [M]) were investigated under two planting densities (5000 and 10000 trees ha−1). The basal diameter and height of dominant shoots were measured at ages 1, 2 and 4 years. The total above-ground fresh weight of individual trees was also measured as an indicator of cumulative biomass at age 4 years. Clonal performance was not significantly changed by the planting density. Repeatability increased slightly from age 1 (0.58) to age 2 (0.65) but decreased by age 4 years (0.33). The highest clonal repeatability (0.54) value for above-ground fresh weight was observed for the T✕D cross, whereas the minimum value (0.27) was obtained when genotypes of all crosses were pooled. The age-to-age genetic correlations indicate high clonal stability over time. With respect to the complexities and time required for screening a large number of genotypes under SRC, the results of this study indicate that traits measured during the first growing season are stable indicators of clonal performance in SRC systems.