Species diversity and dominant species’ niches of eremophyte communities of the Tugai forest in the Ebinur basin of Xinjiang, China

Abstract

Patterns of species diversity are determined by both species interactions and environmental adaptations. The species composition and environmental factors of the Tugai forest on the north shore of the Aqikesu River was investigated to determine species diversity and the ecological niche of dominant species in the Ebinur basin. Using a multivariate regression tree based on the content of soil water and salinity, our results showed that the plant communities were divided into three associations. The three associations are the Ass. Populus euphratica – Apocynum venetum – Phragmites australis (type I), the Ass. Populus euphratica – Reaumuria songonica (type II), and the Ass. Kalidium foliatum ǁ Populus euphratica – Apocynum venetum + Alhagi sparsifolia (type III). Association I had a weak ability to tolerate extreme environments, including 5 quadrats, while Association II could tolerate mild salt and drought stress, including 3 quadrats, and Association III had a certain degree of adaptability to salty and dry habitats, including 22 quadrats. With succession of typical associations from type I to III, psammophytes and halophytes gradually occupied the habitats and become the dominant species. The Shannon-Wiener biodiversity index and Margalef richness index initially decreased and then increased along with environmental degradation, while the Simpson dominance index and Pielou evenness index showed the opposite trend. The variation of associations and species diversity along the environmental gradient reflects the succession of plant communities. The Bray-Curtis similarity analysis of niche breadth clustered 13 dominant species into two groups, with an average similarity of 96.89% and 97.66%, respectively, reflecting that the niche breadth of species has a high similarity. The pressure coefficient of non-metric multidimensional scaling (NMDS) ordination was 0.04 and except for Halimodendron halodendron and Glycyrrhiza uralensis, and species distribution also had a high similarity. In summary, soil water and salt contents are the main environmental factors that are responsible for plant structure and diversity, and determine the direction of succession. The niche and distribution of dominant species show high similarity, indicating obvious competitive relationship between them.