Tree species diversity, composition, population structure and associated herbivore abundance in human-impacted and non-impacted areas of marang’ forest, northern Tanzania

Abstract

Forest resources are mainly conserved in protected areas under various management regimes. The present study aimed at understanding the impacts of changing the status of Marang’ Forest (MF) in Northern Tanzania to a higher-ranked protection status on its tree-species diversity, composition, structure and mammalian-herbivores richness and abundance. Transects and concentric circular plots were used to identify tree species, count stems, measure tree diameter, assess indicators of disturbances and count the signs of large mammalian-herbivores in human impacted and non-impacted areas. The results show that tree species richness and Shannon’s diversity index were about one-third and 17% higher in impacted areas than in non-impacted areas (t = 5.03, p < 0.001; t = 4.98, p < 0.001), respectively. The average number of tree stems ha-1 in impacted areas was significantly higher than the non-impacted ones (t = 3.46, p = 0.01). The impacted areas mostly contained seedlings, saplings and sub-mature trees of pioneer tree species, while the non-impacted ones contained more mature tree stems (F = 16.8, p < 0.001), including endangered species such as Prunus africana. The human disturbances included wood extraction, mining, livestock grazing associated with trespassing. The signs of elephants and buffaloes were about 35% more frequent in impacted than in non-impacted areas. These findings reveal that lowering human disturbances by upgrading forests reserve to higher protection status that emphasize more on resource protection enhance forest recovery and improve tree species diversity, composition, and structure as well as the utilization of the forest by large mammalian-herbivores. Governmental and conservation agencies should deter human disturbances to a minimum level to secure forest resources, which are important for providing environmental services.