Abstract: The valley forest in the Ertix River basin is the germplasm bank of Salicaceae species and has important genetic diversity value of Altay Prefecture, Xinjiang Uygur Autonomous Region. It is of great significance for the protection and utilization of precious resources to study the distribution of plant species and vegetation types under the current human activities such as climate change, hydropower project and grazing. In this paper, 80 squares of 20 plots were investigated at 4–8 km intervals in the Burqin River, Haba River and Bilizik River, the constructive species, quantitative characteristics and diameter class structure of the community were analyzed, and the community types were classified. The results showed that, (1) 121 species, 34 families and 91 genera of plants were investigated in the main tributaries of the Irtysh River basin, with a large number of perennial herbaceous plants. (2) Betula pendula and Populus laurifolia were constructive species in Burjin River and Haba River, while Populus alba was constructive species in Bilizik River. Populus nigra, Populus × berolinensis var. jrtyschensis, and Populus canescens are associated species, while Salix alba is mainly distributed alone along the riparian edge and rarely mixed with poplar species. (3) The number of individuals of the dominant tree species Betula pendula reached the maximum at the middle elevation of the three tributaries, while the number of individuals of Populus laurifolia was smaller at the middle elevation. (4) The diameter class structure of tree layer species was greatly affected by grazing in summer, and the individuals of large diameter class were the most, and the number of saplings and seedlings were less. (5) The valley forest communities were divided into 6 formations and 26 associations.

Key words: valley forests, Salicaceae, Ertix River Basin, species composition, community type