Document Type : Research Paper

Authors

• Narjes Hajiabadi ¹
• Mohamad Saghari ²
• Fatemeh Jahanishakib ³

¹ Faculty of Natural Resources and Environment, University of Birjand, Birjand

² Assistant Professor,, Faculty of Natural Resources and Environment, University of Birjand, Birjand

³ Assistant Professor, Department of Environment, Faculty of Natural Resources and

Abstract

     Background and Objectives: Rangelands, as vital renewable resources, face escalating degradation. Cultivating native and medicinal plants constitutes a key restoration strategy that requires precise knowledge of species' ecological niches. Spatial distribution modeling, particularly with Maximum Entropy (MaxEnt), offers a powerful tool for identifying critical environmental factors and predicting potential habitats. This study aimed to model the potential habitat and identify the key environmental factors influencing the distribution of the valuable medicinal plant Thymus vulgaris in the mountainous rangelands of Al-Qourat, South Khorasan Province, with implications for its conservation and sustainable use.
Methodology: Species occurrence data (n = 103) were systematically gathered through comprehensive field surveys within the study area. To ensure robust model evaluation, the dataset was partitioned into a training set (n = 72) and an independent validation set (n = 31). A total of 16 environmental predictors, categorized into four distinct groups—topography (elevation, slope, and aspect), climate (mean, maximum, and minimum temperature, and annual precipitation), soil properties (EC, pH, soil depth, gypsum content, organic matter, and sand, silt, and clay fractions), and anthropogenic pressure (distance to roads and villages)—were integrated and processed using Geographic Information Systems (GIS). Habitat suitability was modeled using the Maximum Entropy (MaxEnt) algorithm (version 3.3.3k), employing 10 Bootstrap iterations, 5,000 algorithm runs, and 10,000 background points. Model performance was statistically validated via the Area Under the Receiver Operating Characteristic curve (AUC). Furthermore, the Jackknife test and percent contribution analysis were implemented to quantify relative variable importance, while response curves were generated to delineate the species' optimal tolerance thresholds across environmental gradients. Finally, the predicted habitat suitability was classified into four distinct tiers.
Results: The MaxEnt model demonstrated excellent predictive accuracy (AUC = 0.93). Based on the Jackknife test and percent contribution analysis, elevation was the most significant predictor, accounting for 82.7% of the model's explanatory power. Other influential variables included aspect (4.4%), slope (3.5%), distance to villages (2.5%), maximum temperature (2.3%), and mean temperature (2.0%), whereas distance to roads was the least impactful variable (0.4%). Response curves indicated that species presence probability increases significantly with higher elevations (optimal range: 1970–2326 m), steeper slopes, and greater distances from anthropogenic disturbances (roads and villages). Regarding edaphic requirements, T. vulgaris thrives in soils with low salinity (optimal EC ≈ 0.57 dS/m), near-neutral pH (optimal ≈ 7.47), and a sandy loam texture (optimal composition: approximately 56.5% sand, 32.5% silt, and 11–11.5% clay). The resulting suitability map revealed that the highest habitat potential is concentrated in the northern sectors and high-altitude regions of the Al-Qurat rangelands, providing a spatial framework for the targeted conservation and sustainable management of this medicinal species.
Conclusion: This study confirms that Thymus vulgaris in the Al-Quroat rangelands is fully adapted to cold, sloping mountainous environments with well-drained, low-salinity soils. The marked sensitivity of this species' distribution to proximity to roads and human settlements indicates its high vulnerability to overexploitation and anthropogenic habitat degradation. The close agreement of these results with studies on other Thymus species in Iran suggests relatively consistent ecological patterns within this genus. The habitat suitability map and identified ecological indicators can serve as a valid document and practical guidance for natural resource managers and planners. It is suggested that effective steps be taken to protect the genetic resources and sustainable productivity of this valuable medicinal plant by implementing temporary protected areas in high-desirability habitats, establishing wise exploitation programs, and promoting domestic cultivation of this species in identified susceptible lands. Conducting similar studies by integrating different models and considering climate change scenarios for future projections of the species' distribution can complement the present study.

Keywords

• Plant distribution
• Thyme (Thymus vulgaris)
• Habitat modeling
• Rangelands
• MaxEnt
• Ecological requirements

Main Subjects

• Identification, introduction, ecology and ethnobotany