Analysis of the population spatial distribution patterns of wet and saline ecotype Phragmites australis in the oasis-desert transition zone of the Hexi Corridor

The vegetation growth and health status in the oasis-desert transition zone of the Hexi Corridor plays a decisive role in the stability of the oasis. The experimental plots used in this study were set up at wetland and saline habitats with a natural distribution of Phragmites australis population. The spatial distribution patterns of wet P. australis and saline ecotype P. australis population were subsequently investigated. Six kinds of aggregation indexes and Iwao model were used to comprehensively analyze the distribution pattern and aggregation intensity of P. australis populations in different sampling scales and height grades, to obtain information for the investigation of the population behavior and population diffusion type. Our results showed that: both the wet P. australis and saline P. australis population spatial distribution patterns were measured by cluster distribution on six scales, with sampling areas of 4, 8, 16, 20, 40 and 100 m², and saline P. australis showed a random distribution trend. The aggregation intensity of wet P. australis was higher than that of saline P. australis, which meant that the wet habitat was more beneficial to improve aggregation intensity than saline habitats. The aggregation intensity of wet P. australis and saline P. australis were similar in different sampling scales. At all height classes, the aggregation intensity of wet P. australis was higher than that of saline P. australis, especially at the Ⅴ and Ⅵ grades, where the wet P. australis aggregation intensity was the highest. There was a certain random trend at the Ⅱ, Ⅲ, Ⅳ, and Ⅵ height classes of the saline P. australis but no random trend at the Ⅰ and Ⅴ height classes. As water was not the limiting factor for the growth of P. australis in the wet habitat, the population aggregation intensity of P. australis was higher than that in the saline habitat. Owing to the saline stress and water deficit in the saline habitat, the development of the P. australis population in the saline habitat was limited; in order to acquire more water and nutrients, the P. australis population in the saline habitat showed random distribution trend, so as to get more space and resources for its survival and expansion.