Abstract

Understanding the relationship between stem radial growth and climatic conditions in plantation productivity is important to identify the climatic factors that most influence tree growth. This study aims to determine the climatic factors that most influence the stem radial growth of eucalypt trees plantation in the coastal Zululand area of South Africa. Daily stem radius was measured using automated point dendrometers located on 18 sample trees of Eucalyptus grandis × Eucalyptus urophylla (GU) and E. grandis × Eucalyptus camaldulensis(GC) hybrid clones. Daily averages of climatic data (temperature, solar radiation, relative humidity and wind speed) and total rainfall were also obtained from the site over the study period. Several statistical models that cope with the issue of multicollinearity were applied. Weather variables, together with tree age, explained a substantial amount of the variation (87% for GC clone and 79% for GU clone) in the daily stem radius. This study indicates that tree age is the most important factors that influence stem radius during the juvenile stage (up to 2 years) in all seasons. In winter, temperature, relative humidity and wind speed appear to be more important than the other weather variables.

Key words: Tree radial growth, latent variables, multicollinearity, ordinary least squares, partial least squares, principal component regression, plantation.