Dominant population distribution and community gradient changes of Nitraria tangutorum in the northeastern Ulan Buh Desert

Nitraria tangutorum, a common sand-fixation plant in the desertificated areas of northern China, is widely distributed in the northeastern Ulan Buh Desert. To better understand the population ecological process and local community developmental changes of Nitraria tangutorum, it is important to study its population distribution and gradient changes. We studied the populations and communities of Nitraria tangutorum in four sample plots in the northeastern Ulan Buh Desert, which were located between the Yellow River bank and the Langshan piedmont. We analyzed the survey results with the point pattern analysis method to elucidate the population and individual spatial distribution pattern of Nitraria tangutorum. We further explored the relationship between the community and the ecological environment through species-quadrat ordination analysis. Our results indicated that the population spatial distribution pattern of Nitraria tangutorum is closely related to the spatial scale, plant biological characteristics, and ecological environment. The populations of Nitraria tangutorum were regularly distributed at small spatial scales, but can become randomly distributed when the spatial scale reaches a threshold. Compared to the populations close to the Yellow River, those close to Langshan Mountain showed greater extents of regular distribution at small scales and random distribution at large scales. With the gradient alteration of the ecological environment of the sample plots, the plant species distribution of the Nitraria tangutorum communities also showed a gradient changing pattern from the Yellow River bank to the Langshan piedmont. Our results elucidated the spatial distribution difference of dominant Nitraria tangutorum populations between the Yellow River bank and the Langshan piedmont, as well as the gradient changing pattern of the Nitraria tangutorum communities.