A plot-based dataset of Juniperus przewalskii forests

The Juniperus przewalskii forests is a unique vegetation type that only appear in China. They are widely distributed in the mountains of the northeastern edge of the Qingzang Plateau, which became a representative community of the alpine timberline and the forest-grass ecotone. Such forests play crucial roles in slope protection, soil conservation, water source preservation, and habitat improvement. A systematic study on their distribution, composition, and characteristics can provide a scientific basis for the current protection, utilization, and sustainable management of J. przewalskii forests. We conducted a comprehensive survey of J. przewalskii forests throughout the growing seasons from 2018 to 2022. We set up 53 new survey plots and compiled data from 20 historical survey plots; the results covered the entire distribution area of J. przewalskii forests. Through community quantitative statistics and cluster analysis, the main results are as follows. (1) J. przewalskii forests are primarily distributed on sunny and semi-sunny mountain slopes from 2 800 to 3 800 m. They usually occupy harsh environment that is dry, barren, and steep slopes. The existing forests are mostly climax communities after secondary successions. Such forest stands are relatively sparse, with a canopy coverage of 0.2 to 0.6 and an average height from 5 to 13 m. The vertical structure consists of the tree layer, shrub layer, and herb layer. The tree layer is dominated by J. przewalskii, and the diameter class structure shows a right - skewed normal distribution, with the diameter at breast height mainly distributed in the 4–8 cm range. The shrub layer and herb layer vary greatly with changes in habitat conditions. (2) A total of 370 species of vascular plants have been recorded, which belong to 48 families and 151 genera. Among them, there are 45 families, 148 genera of angiosperms, 2 families and 2 genera of gymnosperms, and 1 family and 1 genus of pteridophytes. The top three dominant families are Asteraceae, Poaceae, and Fabaceae. There are obviously more herbaceous species than woody species in terms of the composition of vegetation forms. (3) Juniperus przewalskii forests can be further classified into 11 association groups and 25 associations based on the dominant and characteristic species of the community. The spatial distribution exhibits a clear ecological sequence, including (from low to high altitude) J. przewalskii - Berberis diaphana - Herb Association Group, J. przewalskii - Dasiphora fruticosa - Herb Association Group, J. przewalskii - Dasiphora parvifolia - Herb Association Group, and J. przewalskii - Dasiphora glabra - Herb Association Group. In areas with significant human disturbance, the shrub layer in the community is poorly developed and gradually develops into Juniperus przewalskii - Herb Association group.