ANCHORAGE AND STABILITY OF THREE MAJOR PLANTATION FOREST SPECIES IN VIETNAM

Abstract

Pulling experiments were conducted to determine the mechanical resistance of trees to overturning. We selected two different sites in Vietnam with three major plantation forest species (Acacia hybrid, Eucalyptus urophylla and Pinus caribaea) to determine the correlation between tree stability or stembase inclination index (stiffness index, SI) and tree characteristics (e.g. tree size, tree species, DBH and height), and site conditions. Statistical analyses based on Cox regression model and generalised linear mixed models (GLMMs) showed that tree stability was strongly affected by tree characteristics and site. There was a positive relationship between the risk of tree failure and tree size, in which tree size was the best indicator for all models (Akaike information criterion of 180, p < 0.05), and the tree resistance probability to uprooting increased as tree size increased. In addition, the hazard ratio varied significantly among sites, and between A. hybrid and E. urophylla. It was also found that the SI increased with increased tree size and was highly affected by species. The study confirmed that site conditions affected tree species vulnerability, induced by wind damage, and provided information for further development of mechanistic wind damage risk assessment models for each specific tree species, especially in the tropical forest.