Effects of Site Burning on Multiple Leader Formation and Growth Performance of Selected <i>Acacia</i> Genotypes

Abstract

Loss of apical dominance, resulting in seedlings with more than one leader, generally referred to as multiple leaders (ML), has been a major problem in forest tree plantation in the tropics. A study to examine the effects of site preparation by burning on growth performance and multiple leaders (ML) formation, and its variation in eight-genotypes of <i> Acacia mangium </i> and <i> Acacia auriculiformis </i> was conducted. The design used for this field trial is a randomized complete block design with four replications at two sites (burnt and unburned) and eight genotypes (four from each species), and the effects were monitored for 24 months. There were significant differences at P < 0.05 between sites and genotypes for the number of ML trees/plot, basal diameter and survival. Differences among the genotypes, in terms of height, were also significant, but not between sites. The site × genotype interaction was significant only for ML trees per plot. Generally, the number and the size of ML trees per plot in the burnt site were higher and bigger than those in the unburned site. The number of ML trees per plot formed increased exponentially with time, reaching a peak in about four months after their first occurrence and then leveled off to an almost steady state thereafter at both sites. The average number of multiples (leaders) per tree ranged from 2 to 5 at the burnt site whilst at the unburned site, all the ML trees were of two leaders. <i> A. mangium </i> provenances were more responsive to burning than <i> A. auriculiformis </i> , whereas at the unburned site, the variation between them was not significant. Based on the above variation, it can be concluded that burning causes ML formation and can affect the growth of these selected <i> Acacia </i> genotypes.