Influence of groundwater depth and stand structure on diversity of the understory herbaceous plants in Populus euphratica forests

【Objective】Populus euphratica is widely grown in Xinjiang, Northwestern China. The growth and development of its understory herbaceous plants are influenced by various factors. This paper investigates how groundwater depth, soil moisture, and the stand structure affect the biodiversity of these herbaceous plants.【Method】The analysis was based on data on diversity of the understory plants, groundwater depth, and soil physical properties collected from three representative Populus euphratica forests in the Ejina Oasis.【Result】① The richness and Shannon-Wiener diversity index of the herbaceous plants were negatively correlated with groundwater depth, stem diameter at the breast height (DBH), and soil nitrogen content, while they were positively correlated with stand density and soil moisture. ② Groundwater depth, stand structure, and soil moisture collectively explained 37.60% and 48.60% of the variation in species richness and the Shannon-Wiener index, respectively, indicating that these factors interact to shape the diversity of the understory herbaceous plants. ③ Soil moisture was the dominant driver, explaining 24.05% and 23.89% of the variation in species richness and the Shannon-Wiener index, respectively, and playing a key role in shaping the plant diversity. ④ Groundwater depth explained 11.14% and 12.36% of the variation in species richness and the Shannon-Wiener index, respectively, influencing the diversity both directly and indirectly through its regulation of stand structure and soil moisture. ⑤ DBH directly impacted species diversity, while stand density affected the diversity indirectly by altering soil moisture.【Conclusion】Groundwater depth and stand structure regulate the diversity of understory herbaceous plants primarily through their effects on soil moisture. These findings highlight the integrated roles of hydrology, stand structure, and soil physical properties in shaping the biodiversity of the herbaceous vegetation in the Populus euphratica forests in arid regions.