Tree Species Structure, Composition, and Diversity in Sierra Leone Forest Ecosystem: An Evaluation of Two Protected Forests

Abstract

Biodiversity assessment and forest ecosystem are critical for species conservation. However, limited research had been done in Sierra Leone’s tropical forests. This research explores the feasibility between two different protected areas of forest. This was accomplished by comparing the forest status in terms of tree species composition, diameter at breast height of each tree (to assess basal area), tree species density, and species abundance. Systematic sampling design, with a total of 15 sampling plots each, were districted in both forest ecosystems. All tree species (dbh ≥ 10 cm) in every plot were classified and their height, diameter at breast height (dbh) and diameters at the top, middle and base were evaluated for Otamba Kilimi National Park (strictly protected) and Kangari Hills Forest Reserve. There were 180 individual trees belonging to 24 species in the National Park, and 155 individual trees belonging to 58 species in the Forest Reserve. The most abundant species in the Forest Reserve was Xylopia aethiopica with 25 species compared to the National Park, which was dominated by Spondias mombin with 35 individual species. The Forest Reserve had a higher Shannon-Wiener index (3.63) and evenness (0.89) than the National Park with Shannon-Wiener index (2.76) and evenness (0.87). The Forest Reserve had a higher basal area (33 m2 ha-1) and volume (741.32 m3 h-1) compared to the National Park with a basal area (12.42 m3 ha-1) and volume (184.42 m3 h-1). Results indicate that the Forest Reserve is a potential biodiversity hotspot compared to the National Park. We conclude that the National Park is of lower tree diversity than the Forest Reserve by a degree that probably varies depending on improved management strategies, reforestation measures such as seed regeneration and/or enrichment planting, which will facilitate the gradual return of complex forests. The information on tree species structure and composition can provide baseline information for biodiversity conservation of protected forests in the country.