nassim shabani; Mostafa Tarkesh Esfahani; Alireza Rajabi Mazhar; Nafiseh Salahi Moghadam; Peyman Akbarzadeh; Hasan Shadman; Mehdi Khoshbakht
Volume 32, Issue 2 , July 2025, , Pages 185-200
Abstract
Background and ObjectiveClimate 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 ...
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Background and ObjectiveClimate 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 MethodsIsfahan 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. ResultsAll 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. ConclusionClimate 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.
Farhad Aghajanlou; Peyman Akbarzadeh; Alireza Eftekhari
Volume 31, Issue 4 , January 2025, , Pages 323-346
Abstract
Background and Objectives
Growing awareness of environmental issues and sustainable natural resource management require continuous study and monitoring across various timescales and locations. Ecosystems, including rangelands, undergo constant change. Given their ecological significance, economic ...
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Background and Objectives
Growing awareness of environmental issues and sustainable natural resource management require continuous study and monitoring across various timescales and locations. Ecosystems, including rangelands, undergo constant change. Given their ecological significance, economic role, and vulnerability to irreversible alterations, rangeland monitoring is essential for their ongoing assessment.
Research Methodology
This study monitored changes in vegetation cover and soil indicators over five years at the Dagestan site in Zanjan Province. Field evaluations included plant and soil factors. Plant-related data encompassed canopy cover percentage, litter percentage, species density (where applicable), production, rangeland condition, and trend. Assessments were conducted using established methods, with adequate sampling and proper distribution across different plant communities during both initial evaluation and subsequent monitoring. Soil factors included pH, electrical conductivity, nitrogen, phosphorus, potassium, organic matter content, bulk density, and soil texture.
Results
Statistical analysis of vegetation changes and their effects on soil indicators under grazing and flooding over the five years revealed significant differences in most parameters. Total canopy cover and rangeland production differed significantly between years and site types (grazed vs. exclosure) at the 1% and 5% probability levels, respectively. The highest vegetation cover (56%) was observed in the grazed area in 2018, while the lowest (30%) occurred in the exclosure in 2021. Peak total production (126 g m<sup>-2</sup>) was recorded in the exclosure in 2018, while the lowest (48.7 g m<sup>-2</sup>) occurred in the exclosure in 2021. Total species density showed no significant differences between years, site types, or their interaction. However, on average, shrub density was higher outside the exclosure, while grass density was higher inside, indicating a significant difference. Vegetation changes due to grazing and flooding affected certain soil parameters. Increased grazing intensity correlated with decreased potassium, phosphorus, nitrogen, organic carbon, and electrical conductivity in the topsoil.
Conclusion
Over the five-year study period, grazing significantly influenced vegetation, and the decline in vegetation cover had a notable impact on soil physical and chemical properties. Vegetation changes in the study area were gradual and shaped by rangeland management practices. Regular monitoring of qualitative and quantitative changes in rangeland vegetation is essential for informed planning and the implementation of effective management strategies for sustainable rangeland use.