Objective The Qinghai-Tibet Plateau in the northwestern China is one of the most sensitive regions to global climate change. The northeastern part of Qinghai Province is an important distribution area of forests on the Qinghai-Tibet Plateau. Exploring the biotic and abiotic driving factors of the understory species diversity on the northeast of Qinghai Province can provide a scientific basis for species diversity protection and forest management under climate change.

Method Based on the field survey data of understory species diversity of 29 tree quadrats, 116 shrub quadrats and 116 herb quadrats in the northeast of the Qinghai-Tibet Plateau, the relationships between understory diversity and biotic (stand structure), abiotic factors (including climate, topography and soil) were analyzed by the generalized linear model (GLS).

Result The main results showed that: (1) the species composition of forest community in northeastern Qinghai Province was single, mostly pure forest, and the species diversity was mainly contributed by understory vegetation. A total of 108 species of vascular plants belonging to 89 genera and 44 families were found in 29 quadrats. Rosaceae, Caprifoliaceae and Berberidaceae were the main species. The diversity of herbaceous species was significantly higher than that of shrub species (P < 0.001). (2) Climate and stand structure were the most important driving factors, accounting for 34.9% and 26.2%, respectively. (3) The key driving factors of species diversity of shrub layer and herb layer were different. The species diversity of shrub layer was mainly affected by stand structure (44.0%), and the species diversity of herb layer was mainly affected by abiotic factors such as edaphic (28.8%) and climate (28.2%).

Conclusion There are differences in the driving mechanisms of species diversity between understory shrub layer vegetation and herbaceous layer vegetation in northeastern Qinghai Province. The feedback mechanisms of species at different levels should be fully considered in the process of biodiversity conservation and forest management of forest vegetation community in this region.