Influence of the False Umbrella Thorn (Vachellia reficiens) on Native Tree Species Composition and Diversity in East African Rangelands

Invasive species are known to disrupt native biodiversity, altering plant community composition and ecosystem dynamics. This study examined the influence of Vachellia reficiens, an invasive species, on native plant communities in the Maasai rangelands of Tanzania. Ecological data were collected from 40 paired plots (20 invaded and 20 non-invaded) randomly placed across the landscape, with each plot measuring 50 × 50 m and separated by 50 m to control for environmental conditions. In each plot, all vascular tree species were identified and tree stem counts recorded, with elevation included as an environmental parameter. Species composition and diversity were compared between invaded and non-invaded plots using Shannon-Weiner and Simpson diversity indices. Non-metric multidimensional scaling (NMDS) and Bray–Curtis dissimilarity revealed significant differences in species composition between invaded and non-invaded plots (ANOSIM, R = 0.239, p = 0.001). Indicator species analysis identified several native species, such as V. tortilis (p = 0.001), C. Africana (p = 0.002), V. mellifera (p = 0.004) and S. persica (p = 0.007), as significantly associated with non-invaded plots, indicating their vulnerability to invasion. Diversity indices, species richness (p = 0.011), Shannon-Weiner (p = 0.010) and Simpson (p = 0.015) were significantly lower in invaded areas, suggesting reduced diversity. Although elevation had a lesser influence, it slightly improved model fit. The results suggest that V. reficiens reduces spatial heterogeneity; hence, it homogenises plant communities and lowers native species diversity. Management efforts should prioritise controlling the spread of V. reficiens to protect the biodiversity and ecological health of the rangelands.