Spatial variation in morphological traits of natural Haloxylon ammodendron populations on the eastern margin of the Badain Jaran Desert

Spatially explicit information on morphological variation within natural Haloxylon ammodendron populations remains limited. We examined size-associated morphological and spatial variation in a natural population on the eastern margin of the Badain Jaran Desert. Plant height, crown diameter, and stem-base diameter were measured for 1,151 individuals. Based on the lower and upper quartiles of stem-base diameter, individuals were classified into small, intermediate, and large stem-base diameter classes. Descriptive statistics and geostatistical analyses were used to characterize morphological variation and model spatial dependence. Mean plant height and crown diameter increased across the small, intermediate, and large stem-base diameter classes. The interpolated maps showed spatial variation in all measured traits. Plant height and crown diameter exhibited partially similar spatial patterns, whereas stem-base diameter showed a different spatial pattern. The fitted semivariogram parameters also differed among traits and diameter classes. The observed differences represent size-associated morphological and spatial variation rather than independently validated age-dependent changes. Because soil moisture, groundwater depth, local topography, wind fields, and plant interactions were not directly measured, the environmental mechanisms underlying the observed patterns remain unresolved.