Growth Habit and Performance of Acacia Mangium and Acacia Auriculiformis Genotypes

Acacia mangium Willd. and A cacia auriculifotmis A. Cunn. ex. Benth. are two of the four fast-growing tropical acacias which have received the highest priority for genetic assessment and improvement. Even though A. mangium was proposed for timber production in a short rotation but experience has shown that it is impeded by its susceptibility to heart rot, the multiple leaders (ML) formation, and the tendency of growth to break off just short of the target of the desired size for sawn timber production. However, the present work investigated the ML formation, its causes and variation and concurrently assessed growth performance and examined the patterns of shoot growth and some physiological traits of eight selected A. mangium and A. auriculiformis genotypes through establishment of a field trial and three related glasshouse experiments. The field trial was a randomized complete block design with four replications utilizing eight genotypes four each of the two species at two sites (burnt and unburned). Results at 23 months showed significant differences (P<0.001) between sites for the number of ML trees/plot, basal diameter, and survival but not for height and between genotypes for ML trees/plot, basal diameter (P<0.001), height (P<0.01) and survival (P<0.05). The site x genotype interaction was significant (P< 0.001) only for ML trees/plot.