Mountain forests play major roles in biodiversity; containing many endemics and species of conservation concern. The diversity and distribution patterns of plants in mountain ecosystems are influenced by various environmental and anthropogenic factors that exhibit heterogeneity over space and time. This study analysed species diversity and distribution patterns on two afromontane rain forests of the eastern Arc Mountains of Tanzania in the west Usambaras and Ulugurus to assess any possible threats to biodiversity conservation in this region. A hundred sample plots (0.02 ha) were established on each of the two mountain ranges in such a way as to cover as much variations as possible from valley bottoms to ridge tops. The analysis was based on species importance values computed from the average of the relative basal area and relative density as well as species frequency. Using different diversity indices, the study showed that the mountains have high species diversity. Eighteen endemic species were identified in the Usambaras and thirty-two in the Ulugurus. These endemics are fairly shared between the two mountains and other mountain massifs of the Eastern Arc. Based on our analysis of species distribution, it was found that the proportion of sparsely (rarely) distributed species was over 30% and 49% for the woody species and total vascular plants, respectively. These findings are important in alerting on possible decline of biodiversity in the region and prompting the development of policies to address rare, threatened, and endangered plant species, which are non-existence in Tanzania. We suggest further surveys in the forests of the Eastern Arc Mountains to determine whether the apparently sparse distribution of some species may be found in reasonable abundances elsewhere and quantify the manner and type of use of the forest resources by surrounding local communities to determine their possible impacts on species distribution. TJFNC Vol. 75 2004: pp. 74-9
