Tree Species Diversity and Dominance in Gelai Forest Reserve, Tanzania

Abstract

Tree species diversity and dominance of Gelai Forest Reserve, an isolated montane forest located in an arid area of Northern Tanzania remains unknown. A systematic grid of 390 m x 780 m between 100 plots of 0.02 ha, along nine transects was used during the forest survey. The tree species present, location, diameter above breast height (dbh) and botanical names were recorded including regenerants of tree species and key shrub species. These parameters were then used to determine species diversity index, dominance index, number of tree species regenerants, number of stems per ha and tree basal area per ha. A total of 39 tree species were recorded. The tree species with the highest importance values were Nuxia conjesta (70.7), Olea europaea (44.4) and Crotalaria stulhmanii (40.4). The Simpson index value ranged between 0.0 and 0.034; with Crotalaria stulhmanii having the highest (0.034) index. The tree species diversity index ranged between 0.016 and 0.313. Forest stocking was 377 stems per ha while species basal area ranged between 0.098 m2 and 439 m2 per ha, with Nuxia congesta occupying the highest (439.07 m2 per ha) area and Acacia rovumae the lowest (0.098 m2 per ha), respectively. Seventy nine regenerants were recorded on 9% of the plots. Shrubs, herbs and grasses were found on 55% of the plots mainly without trees dominated by Vernonia galamensis, Leonatis leonorus, Ocimum suave and Solonum incanum. In conclusion, the forest has high tree species diversity which is a good stand characteristic of a natural forest. This survey established a baseline for future monitoring of the forest performance after mitigation of human activities.