Abstract:

Aims Many desert plants show clumped or aggregated distribution patterns, but the adaptive advantage of this spatial pattern is rarely studied. We selected several representative desert plant communities in Sand Lake, Ningxia Autonomous Region and examined the distribution patterns of common desert species to determine adaptation to arid conditions through aggregation. Aggregation was measured by the clump diameter of the caespitose species and the aggregation scale of the scattered species, and relationships between degree of aggregation and soil properties were examined. 
Methods We used point pattern analysis to calculate the aggregation scale of scattered species in plots and collected data on soil steady infiltration rate and community characteristics such as species composition and abundance, as well as diameters and central coordinates of individuals or clumps. Soil moisture content was measured in five different depths: top soil, 0-10 cm, 10-30 cm, 30-60 cm and 60-100 cm.
Important findings Caespitose and scattered species have different degrees of aggregation in different communities. Herbaceous caespitose species, such as Achnatherum splendens, usually had a lower degree of aggregation with better site conditions. A. splendens had the smallest average clump diameter in the only plot with a tree canopy that blocked direct solar radiation and reduced evaportranspiration. Other caespitose species exhibited a similar phenomenon, e.g., the clump diameter of Nitraria tangutorumwas the largest in a plot where habitat conditions were poor. Scattered species had a higher
degree of aggregation in a plot that had a high steady infiltration rate, indicating that high soil permeability could enhance the degree of aggregation. Point pattern analysis indicated a wide range of aggregation of Reaumuria soongoric in plot 3 (0-2 m, 2.3-3.75 m and 4-4.5 m), while another dominant, Kalidium foliatum, was aggregated at 0-5 m. The study indicates that aggregation of desert plants is correlated with habitat conditions. The degree of aggregation tends to be greater in habitats with high solar radiation, hot and dry wind, open stand structure, high soil moisture content and high soil hydraulic permeability. Low aggregation is associated with low transpiration stress and soil water supply. Desert plants could form a micro-habitat by aggregation, reducing evaportranspiration stress and serving as an important adaptive strategy at the community level.