Chronosequence influences plant composition and diversity of Caragana intermedia plantations in an alpine sandy area

Caragana intermedia plantations in the Gonghe Basin of Qinghai Province were taken as the research objects, and herbaceous abundance was investigated at seven sites: 7-yr restoration, 9-yr restoration, 12-yr restoration, 16-yr restoration, 20-yr restoration, 34-yr restoration, and mobile sand dunes (CK). Our objectives were to untangle the dynamics of species composition, functional groups, and plant diversity during the restoration process and to provide a scientific basis for desertification control and ecological restoration of alpine sandy areas. The results showed that 1) the number of herbaceous species increased during the restoration process. Species composition comprised two annuals and biennials (AB) of Chenopodiaceae in CK; a perennial rhizome grass that emerged in 7-yr to 12-yr restorations; AB of Compositae, Poaceae, and Cruciferae, and a newly appeared forb of Compositae in 16-yr and 20-yr restorations; and the presence of two additional perennial bunchgrasses in 34-yr restorations. 2) AB were dominant in each chronosequence, with abundance dynamics being the same as community abundance; both increased and were the highest in the 16-yr restoration and then decreased as the restoration process progressed. The abundance of perennial grasses was constant in 7-yr to 16-yr restorations, and was the highest in 20-yr and 34-yr restorations. Forbs were absent in sites younger than 12-yr, whereas their abundance was the highest in the 34-yr restoration. 3) The species richness, Shannon-Wiener index, and Simpson index of the plant community increased, but the evenness index decreased during the restoration process. AB remained dominant in each chronosequence and the diversity indices did not exhibit a threshold, indicating that the plant community and diversity still have the potential for further recovery.