Influence of Environmental Factors on the Distribution Pattern of Astragalus adscendens in Lorestan Province Using the MaxEnt Model

ABSTRACT
Understanding the distribution pattern of medicinal plants is essential for identifying the role of climatic and environmental variables. In this study, the distribution of “Astragalus adscendens,” as one of the native species of Lorestan Province, was investigated using the Maximum Entropy (MaxEnt) model. Species presence data were collected through field sampling in the regions of Aligudarz, Azna, Aleshtar, and Nurabad during the spring and summer of 1404. The results showed that cold-season precipitation (Bio19), with a permutation importance of 49.4% and a relative contribution of 26.6%, was the most important distribution factor, and the highest probability of presence was observed within the precipitation range of 100 to 140 mm. Land slope, with a permutation importance of 31.8%, was the second most influential factor; moderate slopes (30–40%) and northern aspects exhibited the most favorable conditions. The optimal temperature for species presence was approximately 13–14°C, and the suitable elevation range was determined to be 2400–2700 m. Loamy soils also provided favorable conditions for species establishment. In general, variables such as elevation, land use, and soil texture played a complementary role, and species distribution was mainly influenced by temperature, winter precipitation, and sloping, snow-covered highlands; only 27.2 square kilometers of the province’s land, mainly in the east and southeast, exhibited moderate to very high suitability, and highly suitable habitats were located in the highlands of Qalikuh, Tamandar, and Oshtorankuh.
Extended Abstract
Introduction
The distribution and long-term persistence of medicinal plant species in Iran are strongly influenced by a range of natural factors and human activities. In recent decades, unsustainable harvesting, extensive land-use changes, overgrazing, habitat fragmentation, and ecosystem degradation have led to a significant decline in the population size and geographic range of many valuable medicinal plants. These threats have been intensified by the absence of comprehensive national strategies for the identification, conservation, and sustainable utilization of native species. The lack of ecological data, the limited scope of long-term monitoring programs, and the absence of reliable spatial distribution maps have collectively constrained effective planning and management of medicinal plant resources at the national level.
In addition to direct human impacts, climate change has emerged as one of the primary drivers of ecological transformations, accompanied by shifts in temperature patterns, precipitation regimes, and an increasing frequency of extreme climatic events such as prolonged droughts. These changes have significantly altered the habitat suitability of many plant species and have led to the degradation, contraction, or displacement of their ecological niches. Mountain ecosystems, despite their ecological importance and high biodiversity value, are highly vulnerable to these changes because of their narrow climatic tolerance range and strong dependence on seasonal precipitation.
“Astragalus adscendens,” as a native perennial species in the central Zagros Mountains, is considered one of the ecologically important species adapted to high-altitude rangelands. This species plays a fundamental role in soil stabilization, erosion control, and the maintenance of rangeland structure and function. Its growth form and root system enhance soil physical properties, increase water infiltration, and reduce surface runoff. Given the ecological importance of this species and its increasing exposure to environmental stresses, identifying the factors controlling its distribution is essential for the development of effective conservation and sustainable management strategies. Therefore, the main objective of this study was to identify the most important environmental variables influencing the spatial distribution of “Astragalus adscendens” and to model its potential habitat suitability in Lorestan Province using the MaxEnt modeling approach.
 
Methodology
The potential distribution of “Astragalus adscendens” was modeled using MaxEnt version 3.3.4. This machine-learning method is widely used for species distribution modeling based on presence data. This approach estimates the most probable spatial distribution pattern based on the relationship between species presence points and a range of environmental variables.
Species presence data were collected during the spring and summer of 2025 from four main habitats in Lorestan Province, including Aligudarz (Qalikuh and Tamandar), Azna, Aleshtar, and Nurabad. The geographic coordinates of each presence point were recorded using a GPS device, and associated ecological characteristics such as elevation, slope, slope aspect, soil type, and vegetation cover were documented through field observations. After data processing to prevent model overfitting, a total of 23 presence points were retained for the final modeling. To control multicollinearity among environmental variables, Pearson correlation analysis was performed, and variables with a correlation coefficient greater than 0.8 were excluded. Finally, 13 environmental variables, including five bioclimatic variables related to temperature and precipitation and eight topographic and environmental variables describing land characteristics, were selected. Model performance was evaluated using the area under the receiver operating characteristic curve (AUC) index. The relative contribution and importance of each variable were determined using the jackknife test, and habitat suitability maps were generated in a Geographic Information System environment and classified into five categories ranging from very low to very high.
 
Results and Discussion
The results showed that the MaxEnt model demonstrated high predictive accuracy in identifying suitable habitats for A. adscendens in Lorestan Province. Among all environmental variables, winter precipitation was identified as the most influential factor affecting species distribution. The highest probability of species presence was observed within the winter precipitation range of approximately 100 to 140 mm, whereas habitat suitability decreased markedly when precipitation exceeded 160 mm. This pattern indicates species adaptation to semi-arid mountainous conditions, where moderate winter moisture facilitates establishment and growth, while excessive precipitation may create unfavorable soil conditions. Slope was identified as the second most important factor in determining habitat suitability. The most favorable conditions were observed on relatively steep slopes (approximately 30 to 40%), particularly on northern and northeastern aspects. These topographic features enhance soil moisture retention, reduce evaporation, and prevent prolonged waterlogging, thereby providing suitable microclimatic conditions for plant growth.
Variables related to temperature, elevation, and soil texture also contributed to the distribution pattern, although their effects were relatively weaker than those of precipitation and slope. Among temperature-related variables, seasonal temperature variation and the mean diurnal temperature range showed the greatest importance. The optimal mean temperature range for species presence was estimated to be between 13 and 14°C, whereas temperatures exceeding 15°C resulted in a considerable decline in habitat suitability. Elevation also restricted the species to the range of 2400 to 2700 m above sea level, where lower temperatures and higher relative soil moisture create favorable growth conditions. In contrast, variables related to land use and soil characteristics showed limited influence, indicating a relatively broad tolerance of the species to different soil conditions. The habitat suitability map indicated that approximately 95% of the area of Lorestan Province is unsuitable for this species. Only approximately 27.2 square kilometers fall within the moderate to high suitability class, mainly located in the highlands of Qalikuh, Tamandar, and Oshtorankuh.
 
Conclusion
This study showed that the distribution of “Astragalus adscendens” in Lorestan Province is primarily influenced by climatic and topographic factors, with winter precipitation and slope exerting the greatest influence. This species exhibits its highest growth potential in cold, relatively dry mountainous environments with moderate winter precipitation and warm summers. Given the dominant role of climatic variables, future changes in temperature and precipitation patterns may substantially alter the extent and spatial distribution of suitable habitats. Therefore, proactive conservation planning, protection of existing high-altitude habitats, sustainable grazing management, control of land-use changes, and continuous monitoring of climatic conditions are essential to ensure the long-term conservation and ecological stability of this species.
 
Funding
This article is derived from a postdoctoral research project supported financially by Lorestan University.
 
Authors’ Contribution
Authors contributed equally to the conceptualization and writing of the article. All of the authors approved thecontent of the manuscript and agreed on all aspects of the work declaration of competing interest none.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
 We are grateful to all the scientific consultants of this paper.