LAUSR

ABSTRACT Success of clonal tree plantations depends on genotype as well as phenotypic plasticity, which determines acclimation potential of individual trees to different environmental conditions. Short-term acclimation of genotypes to local growing conditions can be tested using clonal trials, but stand productivity and yield depends on the ability of the genotype to acclimate to long-term environmental variation. In Japan, clonal plantations of Cryptomeria japonica (Thunb. ex L. f.) D. Don are common and many elite clones have been developed. We evaluated growth of clonal C. japonica plantations in 45-year-old clonal trials taking into account effects of both genotype, environment and their interaction (i.e., phenotypic plasticity). In all five sites, tree sizes were larger for clonal cultivars evaluated initially as “early-growth type” than for the “late-growth type” cultivars. All cultivars showed decrease in tree height from lower to upper slope. The differences in tree growth among cultivars were more marked in sites where trees grew well, suggesting poor site conditions prevented the early-growth cultivars from fully exploiting their growth potential. Phenotypic plasticity of each cultivar was evaluated as growth variation among sites (regional variation) and along slope within sites (topographic variation). Plasticity was observed at both regional and topographic scales and cultivars with higher plasticity generally grew larger. The result of our study suggested that genotypes with greater phenotypic plasticity may possess greater acclimation potential, enabling them to grow well under a wide range of environmental conditions.