Impact of Xanthium. strumarium L. invasion on herbaceous species composition and diversity in Eastern Ethiopian Rangelands

Cocklebur (Xanthium strumarium L.) is one of the most widespread and abundant invasive plants in East Africa, including Ethiopia. It rapidly forms large stands that displace other plant species. Thus, the current study was conducted to assess the effect of X. strumarium on the herbaceous plant species composition and diversity of rangelands in eastern Ethiopia. The study was conducted in six districts, purposefully selected based on the level of X. strumarium invasion in the rangelands of eastern Ethiopia. A total of 72 sample plots consisting of 36 invaded and 36 uninvaded sites were selected using random sampling methods. Plant species composition and abundance were recorded using a 4 m2 quadrat. The collected data were subjected to univariate and multivariate analyses using R version 4.4.1. A total of 85 plant species were found in the uninvaded sites, whereas the invaded sites contained 57 plant species, reflecting a decline of 32.9%. Species richness, Shannon–Wiener diversity index, Simpson diversity index, and Pielou's evenness indicated that the uninvaded sites were more diverse than the invaded sites. A higher Sorensen and Jaccard similarity index of herbaceous plant species was observed at Haramaya (0.75, 0.60), whereas Sofi exhibited the lowest values (0.29, 0.17). The rank abundance curve also demonstrated that species abundance, richness, diversity, and evenness were greater in the uninvaded sites than in the invaded sites. The results of the NMDS and PERMANOVA also revealed that plant species composition and structure were significantly different between the invaded and uninvaded sites. Consequently, X. strumarium is one of the most dominant invasive alien plant species, and poses a severe threat to species diversity, composition, and structure in the rangelands of eastern Ethiopia. Therefore, effective policy planning, strategic intervention, and the adoption of appropriate control and management practices in the rangeland environment are crucial for mitigating the current impact and preventing potential future challenges.