Scale-dependent spatial association of the dominant shrub Calligonum mongolicum and its co-occurring shrubs in an extremely arid desert: Insights from spatial point pattern analysis
LI Jiale1, ZHANG Dinghai1,*(), LU Xudong1, JIA Rongliang2
1Centre for Quantitative Biology, College of Science, Gansu Agricultural University, Lanzhou 730070, China 2Shapotou Desert Experimental Research Station, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
Understanding scale-dependent plant-plant relationships is essential for revealing population organization and species coexistence in extremely arid ecosystems. In this study, Calligonum mongolicum Turcz., a dominant sand-fixing shrub in mobile dunes of the Gurbantunggut Desert, Northwest China, was selected as the focal species to investigate its intra- and interspecific spatial relationships across multiple scales. Univariate, bivariate, and marked point pattern analyses combined with different null models were applied to characterize spatial patterns between different life stages, survival statuses, individual sizes, and co-occurring shrubs, and to evaluate the potential contributions of habitat heterogeneity and dispersal processes. The results show that the overall population and different life stages of C. mongolicum exhibited significant aggregation under the complete spatial randomness model, whereas the aggregation patterns were largely weakened after accounting for habitat heterogeneity and clustering processes. Adult-juvenile spatial associations showed clear scale dependence, whereas survival-related spatial patterns exhibited limited spatial dependence. After accounting for habitat heterogeneity, no persistent spatial pattern supporting strong adult-mediated facilitation or density-dependent effects was detected across most scales. Interspecific associations between C. mongolicum and co-occurring shrubs (Haloxylon persicum Bunge ex Boiss. & Buhse, Artemisia ordosica Krasch., and Ephedra distachya L.) also exhibited pronounced scale dependence, with positive associations mainly occurring at smaller scales and negative associations emerging at some larger scales. These findings indicate that the spatial organization of dominant desert shrubs is shaped by multiple ecological processes, including habitat heterogeneity, dispersal limitation, and potential biotic interactions, providing new insights into plant coexistence and population maintenance in extremely arid ecosystems.
Received: 17 March 2026
Published: 31 October 2026
Formal analysis: LI Jiale; Writing - original draft preparation: LI Jiale; Writing - review and editing: ZHANG Dinghai, LU Xudong; Project administration: JIA Rongliang; Supervision: JIA Rongliang. All authors approved the manuscript.
LI Jiale, ZHANG Dinghai, LU Xudong, JIA Rongliang. Scale-dependent spatial association of the dominant shrub Calligonum mongolicum and its co-occurring shrubs in an extremely arid desert: Insights from spatial point pattern analysis. Journal of Arid Land, 2026, 18(10): 1831-1849.
Fig. 1Overview of Xinjiang Uygur Autonomous Region of China based on the elevation and sampling locations. Noted that the figure is based on the standard map (No. 新 S(2021)023) of the Xinjiang Uygur Autonomous Region Platform for Common Geospatial Information Services (http://xinjiang.tianditu.gov.cn/bzdt_code/bzdt.html#) marked by the Department of Natural Resources of Xinjiang Uygur Autonomous Region, and the boundary of the base map has not been modified.
Fig. 2Spatial distribution of the Calligonum mongolicum Turcz. population. (a), overall spatial distribution of the C. mongolicum population; (b), distribution of dead and living individuals; (c), distribution of adult and juvenile individuals. The original geographic coordinates referenced to the WGS84 geodetic system were first transformed into planar metric coordinates. The lowest-elevation location among all recorded individuals of C. mongolicum within the plot was then selected as the spatial reference origin. The relative x-coordinate and relative y-coordinate represent the horizontal and vertical distances, respectively, of each individual from this reference point in the transformed planar coordinate system, with units of meters. In all panels, the size of each circle represents the relative volume of the corresponding plant, with larger circles indicating larger plant volumes.
Fig. 3Spatial distributions of C. mongolicum and the co-occurring shrubs Haloxylon persicum Bunge ex Boiss. & Buhse, Ephedra distachya L., and Artemisia ordosica Krasch. The relative x- and y-coordinates are expressed in meters and were obtained using the same coordinate transformation and spatial reference procedure as those described for Figure 2.
Research category
Analysis component
Null model
Summary statistic
Intraspecific analysis
Spatial patterns of the overall population and life stages
CSR, HPP, and TH
g(r)
Life-stage spatial association
Bivariate CSR, and Bivariate HPP
g12(r)
Life-stage volume association
IM
ymm(r)
Spatial pattern of dead individuals
CSR RL
g(r)
Dead-living spatial association and differences in aggregation intensity
RL
g12(r) g22(r)-g11(r)
Potential nurse effect
RL
P(r)
Density-dependent effect
RL
g1,1+2(r)-g2,1+2(r)
Interspecific analysis
Interspecific spatial association
Bivariate CSR, Bivariate HPP, and TS
g12(r)
Table 1 Summary of spatial point pattern analyses, null models, and summary statistics used in this study
Fig. 4Intraspecific quantitative composition and morphological characteristics of C. mongolicum. (a), survival status of C. mongolicum individuals; (b), developmental stages of C. mongolicum individuals.
Species
Number
Percentage of population (%)
Height (cm)
Crown width in east-west direction (cm)
Crown width in north-south direction (cm)
Calligonum mongolicum Turcz.
481
38.4
40.92±0.98
84.24±2.57
86.99±2.63
Artemisia ordosica Krasch.
334
26.7
32.17±1.07
46.34±1.55
47.63±1.91
Ephedra distachya L.
96
7.7
55.70±2.75
242.36±14.47
260.90±15.26
Haloxylon persicum Bunge ex Boiss. & Buhse
341
27.2
75.52±4.43
49.62±3.17
51.49±3.66
Table 2 Quantitative composition and morphological characteristics of sand-fixing shrub communities
Fig. 5Spatial patterns of juvenile, adult, and overall C. mongolicum populations under complete spatial randomness (CSR; a-d), heterogeneous Poisson process (HPP; e-h), and Thomas process (TH; i-l) null models. The red line represents the observed values, the blue line represents the theoretical expectation, and the grey shaded areas represent the 95.0% simulation envelopes generated from 199 Monte Carlo simulations, with black boundary lines indicating their upper and lower limits. Green solid circles indicate significant aggregation, open circles indicate random distributions, and g(r) denotes pair correlation function used to characterize univariate spatial patterns.
Fig. 6Spatial associations between juvenile and adult C. mongolicum under bivariate CSR (a and c) and HPP (b and d) null models. The red line represents the observed values, the blue line represents the theoretical expectation, and the grey shaded areas represent the 95.0% simulation envelopes generated from 199 Monte Carlo simulations, with black boundary lines indicating their upper and lower limits. Green solid circles indicate significant positive spatial associations, open circles indicate no significant spatial association, and g12(r) denotes cross pair correlation function used to characterize spatial associations between two point types.
Fig. 7Intraspecific association analysis of C. mongolicum based on survival status and volume marks. (a), analysis of potential nurse effects; (b), density-dependent effects among juveniles; (c-d), volume-related spatial dependence among juveniles and adults, respectively; (e), volume-related spatial dependence between adults and juveniles. The red line represents the observed values, the blue line represents the theoretical expectation, and the grey shaded areas represent the 95.0% simulation envelopes generated from 199 Monte Carlo simulations, with black boundary lines indicating their upper and lower limits. P(r), conditional probability function used to evaluate juvenile survival probability in relation to adults; g1,1+2(r)-g2,1+2(r), difference in neighborhood density used to evaluate density-dependent effects; ymm(r), mark variogram used to evaluate spatial dependence in plant volume; ym1m2(r), bivariate mark variogram used to evaluate spatial dependence in plant volume between different life stages.
Fig. 8Spatial distributions and associations of dead and living individuals of the dominant shrub C. mongolicum. (a), spatial pattern of dead individuals of C. mongolicum under the CSR null model; (b), intraspecific aggregation intensity of dead individuals relative to living individuals; (c), spatial pattern of dead individuals of C. mongolicum under the random labeling (RL) null model; (d), spatial association between dead and living individuals. The red line represents the observed values, the blue line represents the theoretical expectation, and the grey shaded areas represent the 95.0% simulation envelopes generated from 199 Monte Carlo simulations, with black boundary lines indicating their upper and lower limits. The dots below each subplot indicate the significance of the observed statistics relative to the corresponding null model at different spatial scales: green solid dots indicate that the observed values are significantly higher than the confidence envelope of the null model, and white open dots indicate no significant deviation from the null model.
Fig. 9Spatial associations between the dominant shrub C. mongolicum and three co-occurring shrubs (A. ordosica, E. distachya, and H. persicum) under CSR (a-d), HPP (e-h), and toroidal shift (TS; i-l) null models. The red line represents the observed values, the blue line represents the theoretical expectation, and the grey shaded areas represent the 95.0% simulation envelopes generated from 199 Monte Carlo simulations, with black boundary lines indicating their upper and lower limits. Green solid circles indicate positive spatial associations, and open circles indicate no association.
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