Document Type : Research Paper

Authors

• nassim shabani ¹
• Mostafa Tarkesh Esfahani ²
• Alireza Rajabi Mazhar ³
• Nafiseh Salahi Moghadam ⁴
• Peyman Akbarzadeh ⁵
• Hasan Shadman ⁶
• Mehdi Khoshbakht ⁷

¹ Researcher in the Forests and Rangelands Department of the Agricultural Research, Education and Extension Center of Zanjan Province

² Associate Professor, Rangeland and Watershed Management Group, Faculty of Natural Resources, Isfahan University of Technology, Isfahan, Iran

³ Assistant Professor, Forests and Rangelands Research Section, Hamadan Agricultural and Natural Resources Research Center, AREEO, Hamadan, Iran

⁴ Researcher, Economic, Social and Extension Research Section, Zanjan Agricultural and Natural Resources Research Center, AREEO, Zanjan, Iran

⁵ Researcher, Forests and Rangelands Research Section, Zanjan Agricultural and Natural Resources Research Center, AREEO, Zanjan, Iran

⁶ Researcher, Watershed Management Research Section, Zanjan Agricultural and Natural Resources Research Center, AREEO, Zanjan, Iran

⁷ Watershed Management Expert, Hamadan General Directorate of Natural Resources, Forests, Rangelands and Watershed Management Organization, Hamadan, Iran

Abstract

Background and Objective
Climate change is recognized as one of the serious threats to biodiversity in natural ecosystems, having major impacts on the survival, performance, and distribution of plant and animal species. These changes can lead to alterations in population rates, species extinction, and shifts in the distribution of plant habitats. Therefore, a precise understanding of the climatic niche of species and the prediction of their responses to climate change are essential for natural resource management. Species distribution models (SDMs) are useful tools for predicting habitat changes and assessing the future impacts of climate change. In this study, the performance of three species distribution models, including the Maximum Entropy Model (Maxent), Ecological Niche Factor Analysis (ENFA), and Non-Parametric Multiplicative Regression (NPMR), is compared. The effect of climate change on the distribution of the habitat of Astragalus adscendens is analyzed‌ for the years 2050 and 2100 under the HadGEM-RCP 4.5 scenario using the best-performing model.
 
Materials and Methods
Isfahan Province, covering an area of over 107,000 square kilometers, has a wide range of elevations (707 meters to about 4000 meters) and diverse climatic zones (semi-arid, steppe, semi-steppe, dry forests, and high mountains). The plant species Astragalus adscendens is recognized as a native and significant species of the Iranian rangelands. To model the distribution of this species, 70 presence sites and 70 absence sites were randomly extracted from the vegetation type map of Isfahan Province using a stratified sampling method (Feizi et al., 2017). Additionally, 70 new sites were sampled through field visits in the towns of Semirom and Fereydunshahr using a GPS device for model evaluation data. A total of 22 environmental layers were prepared, including three physiographic variables (slope, aspect, and elevation) and nineteen bioclimatic variables for the present, 2050, and 2100 under the RCP 4.5 climate scenario using the HadGEM2 general circulation model. These variables are derived from three main parameters: monthly precipitation, minimum monthly temperature, and maximum monthly temperature. All environmental layers were prepared with a pixel size of one square kilometer. Finally, three modeling methods Maxent, ENFA and NPMR—were used to predict the distribution of Astragalus adscendens.
 
Results
All three models showed good performance for predicting the habitat of Astragalus adscendens (AUC > 0.85). A reduction in habitat area under the HadGEM-RCP 4.5 climate change scenario is evident in all three models. Annual precipitation was identified as the most significant environmental factor influencing the distribution of Astragalus adscendens. Species response curves for the environmental variables, extracted from the Maxent and NPMR models, suggest that Astragalus adscendens is more prevalent in areas with precipitation over 350 mm and elevations above 2500 meters. The response curve of the species to slope indicates a positive relationship, showing that the likelihood of species presence increases with slope. Based on model evaluation, the Maxent model outperforms the others, showing a higher AUC index.
 
Conclusion
Climate change, particularly reduced precipitation and increased temperatures, will have significant negative effects on the distribution of Astragalus adscendens, such that by 2100, the presence of this species in Isfahan Province, especially in the Fereydunshahr region (western part of the province), will severely decrease. It will only be found in patches in the high elevations of Padanah in the Semirom region. It should be noted that the species distribution models used in this study considered only climatic and topographic conditions, without accounting for other influencing factors such as soil properties, management practices, and biological interactions. Therefore, the results presented can provide a general estimate of the potential distribution of the species under the HadGEM-RCP 4.5 climate scenario, but for more accurate habitat management, further studies incorporating other environmental and biological factors are essential.
 

Keywords

• Astragalus adscendens
• Climate change
• Ecological Niche Factor Analysis Maximum Entropy
• Isfahan Province
• Non-Parametric Multiplicative Regression