An analysis of correlated curve trend experiments in Eucalyptus grandis

Correlated curve trend (C.C.T.) experiments in Eucalyptus grandis on the Zululand coast of South Africa were analyzed. Growth parameters were described as functions of age using Schnute’s generalized growth function and parameter estimates were described as functions of stand density. Growth attributes were used as moments of a probability density function to describe a diameter distribution model for the species. Time trends in the relationships between growth parameters and stand density were scrutinized with multiple comparisons of paired means. It was shown that diameter growth in lower size classes ceases under conditions of extreme suppression while growth continues unabated in the larger size classes, resulting in greater dispersion in diameter. Competition mortality was to a large extent confined to the lower size classes and severe mortality results in an apparent increase in mean diameter which precludes use of growth functions which impose an asymptote. Allometric growth was investigated on two different sites and growth trends were shown to be anamorphic between sites. This permits a ratio approach to the estimation of growth and yield on one site based on experimental evidence from another. Thinning effects in terms of diameter and height changes were estimated from simulated thinnings using data from unthinned stands while the results of long-term thinning studies were compared in terms of cumulative volume yields. The age at which mean annual increment culminates was determined and a model for the estimation of m.a.i. as a function of age and stand density was constructed. A critical examination of spacing indices revealed that the slopes thereof were much steeper than those for many other species. The better-known indices of Reineke and Yoda were found to be dependent on age.