Invasion level had a significant (P < 0.01) effect on the aboveground biomass and basal cover of herbaceous species and on the bare ground cover in both locations (Figs. 5 and 6).
According to Dorning and Cipollini (2006) and Awodoyin and Ogunyemi (2008), the reduction in biomass and basal cover of other herbaceous plant species in the heavily invaded sites might be associated with the early germination and maturation of S. obtusifolia that might take advantage of forming a closed canopy and basal cover over native herbaceous plant species.
The non-invaded sites had a higher aboveground biomass and basal cover of other herbaceous species than the heavily invaded sites (Figs. 5 and 6).
The basal cover of native herbaceous vegetation was found to be much reduced under high P. juliflora infestation.
However, the basal cover of native herbaceous vegetation and native tree diversity were found to be much reduced under high P. juliflora-invaded areas.
In contrast, the biomass and basal cover of S. obtusifolia were significantly (P < 0.01) higher in the heavily invaded sites compared to those in the non-invaded and lightly invaded sites (Table 2).
However, the reported 3237.58 m2∙ha−1 basal cover of 82,383 individuals of woody species was found to be significantly higher than the recorded basal cover of tropical forests (Bhuyan et al. 2003; Kumar et al. 2006).
Moreover, its invasion reduced the biomass and basal cover of native herbaceous vegetation.
The percentage of basal cover of S. obtusifolia and other herbaceous plant species and that of bare ground were estimated visually in each quadrat.
Here, we investigated the species composition, species diversity, aboveground biomass, and basal cover of herbaceous vegetation, as well as soil properties of rangelands along three S. obtusifolia invasion levels.
