Population Structure and Regeneration Status of Trichilia dregeana Sond. in Heavily and Less Disturbed Areas of Kalinzu Forest Reserve, South Western Uganda

Abstract

The population structure and regeneration status of Trichilia dregeana in heavily and less disturbed habitats of Kalinzu forest reserve were assessed in 2013. The species was used locally for medicines, fire wood and making household utensils, a situation that rendered it vulnerable. Given this dependence by local communities, the population of the species was under human pressure due to demand. This necessitated a critical understanding of how the population structure was affected by such disturbance although in some species, population structure disturbance increased resilience. Size-class distribution and regeneration status were used to determine the population structure as influenced by human disturbance. Four plots of 20 × 10 m were randomly established in each forest type and all T. dregeana trees of diameter ≥ 10 cm were counted and their DBH was measured at 1.3 m from the ground. In each of these plots, a 10 × 10 m plot was made and saplings DBH ≥ 2-10 cm were enumerated. Inside each 10 × 10 m plot, a 5 × 5 m plot was made and T. dregeana seedlings (<2 cm diameter) were identified and counted. The density of T. dregeana in the heavily disturbed forest was higher than in the less disturbed forest type. The size-class distribution exhibited a characteristic inverse J-shaped distribution pattern in the heavily disturbed forest whereas it was bell-shaped in the less disturbed forest type. In both forest types, the population of T. dregeana was found to be actively regenerating. This study concludes that the population structure of Trichilia dregeana is dominated by juveniles with total absence of individuals of DBH ≥ 22 cm, due to selective harvesting of mature individuals. In order to stop harvesting of this species from the natural forest, there should be an effort to provide seedlings to local communities so that they grow it on their farms.