Pasture dynamics in the semi-arid mbulu district, Tanzania

The semi-arid vegetation of Mbulu District was studied and the environmental variables influencing species diversity, composition and distribution were quantified. Plant species diversity from the study area was significantly higher in the wet season than in the dry season. The values ranged between 4.17± 0.17 and 3.55 ± 0.267 in the wet season and between 3.46 ± 0.125 and 2.32 ± 0.140 in the dry season. Grazing pressure apart from seasons resulted in a variation in species diversity. With increased grazing pressure, there was a decrease in species diversity. Tragus berteronianus, Hypoestes forskalii, Ageratum conyzoides and Solanum incanum increased in abundance they were identified to be unpalatable species to livestock. CCA ordination analysis of the species data showed a high correlation between species abundance and distribution with grazing intensity, cation exchange capacity, soil nitrogen, moisture contents, phosphorus and soil organic matter content. These variables were significant on the basis of Monte Carlo Permutation test (P<0.05).