Objectives  To explore the response relationship between plant community diversity and altitude and its driving mechanism in Qilian Mountain Nature Reserve, and to identify the driving mechanisms behind the relationship. The findings will provide a theoretical basis for the conservation and restoration of the regional forest ecosystem, as well as a reference for the protection and utilization of regional biodiversity and ecological construction.

  Methods  On the basis of field sample survey, Detrended canonical correspondence analysis (DCCA), correlation analysis and regression analysis were comprehensively used in this study. The relationship between plant community diversity and altitude in Qilian Mountain Nature Reserve (99°30′−100°53′E, 38°12′−39°17′N, altitude 1 500−3 700 m) was analyzed.

  Results  The results showed that: 1) The richness index and diversity index of plant communities at different levels showed significant differences at different altitudes. The Patrick richness index and Shannon-Wiener diversity index of the herbaceous layer and the shrub layer showed a “unimodal” change pattern with environmental gradient and altitude gradients, except for high altitudes (2 950−3 700 m). In other elevations, the richness index and diversity index of the herbaceous layer were significantly higher than those of the shrub layer (P < 0.01) and reached the highest point in the middle elevation zone (2 400−2 950 m) zone. 2) The uniformity of Pielou did not significantly differ at each level of the plant community with the environmental and elevation gradients. This suggested that the uniformity of the plant community was less affected by the environmental response and was mainly influenced by the community’s structure type and stability. 3) The distribution pattern of herbaceous, shrub, and tree vegetation accounted for 29.32%, 23.24%, and 9.05% by environmental factors, 15.21%, 11.08%, and 7.52% by spatial factors, and 11.04%, 8.42% and 5.31% by the interaction of spatial and environmental factors, respectively. The proportion of unexplained by spatial factors and environmental factors was 44.43%, 57.26%, and 78.12%, respectively.

  Conclusions  The species diversity of plant spieces within a community was influenced not only by the hydrothermal gradient caused by altitude, but also by biological interactions, human activities, development degree, and other factors. In the future protection and management of the ecosystem, measures must be taken to reduce the impact of human activities, and to strengthen efforts to cope with climate change.