Document Type : Research Article
Author
Department of Geography Education, Farhangian University, P.O. Box 14665-889, Tehran, Iran
Abstract
Introduction
Human activities and the substantial increase in greenhouse gas concentrations-particularly carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) have exacerbated global warming and triggered significant alterations in climatic patterns. Consequently, climate change has emerged as a critical challenge for natural resource management and agricultural systems in recent decades. These changes, especially temperature and precipitation fluctuations, directly impact plant phenological and vegetative cycles and may even shift the suitable geographical ranges for cultivating certain plant species. Among these species is Ziziphus jujuba Mill. (Family: Rhamnaceae), a medicinally valuable plant that exhibits relative adaptability to arid and semi-arid climates, such as those in Iran. However, it remains vulnerable to climate change impacts. Historically cultivated in South Khorasan Province, this region now accounts for over 72% of Iran’s jujube production. Investigating climatic trends and their effects on the reproductive and vegetative thresholds of Ziziphus jujuba is both scientifically and practically significant. Such analyses enhance our understanding of regional climate change dynamics and facilitate predictive assessments of its agricultural consequences. Therefore, the objective of the present study was to identify the reproductive and vegetative thresholds of jujube throughout the year in the counties of South Khorasan Province and to spatially analyze these thresholds in terms of temperature and precipitation, both under baseline conditions and future scenarios influenced by trends in temperature and precipitation changes.
Material and Methods
In this study, the modified Mann-Kendall test, Sen's slope estimator, and linear regression analysis were employed to analyze trends in data related to determining the cultivation range of the jujube plant. The study data included monthly temperature and precipitation averages from seven synoptic stations within the study area, covering a statistical period of 25 years from 2000 to 2024. These data were extracted from the National Meteorological Organization and served as the foundation for the study. Station data were converted into z-scores using the modified Mann-Kendall test in Minitab software. Additionally, linear trends of variables such as minimum temperature, maximum temperature, mean temperature, precipitation, sunshine hours, and hot days, along with their corresponding slopes, were examined.
Results and Discussion
Jujube plants, like other plant species, require specific temperature ranges for optimal growth during different vegetative and reproductive stages. This study examined the thermal thresholds that impact the growth of jujube trees. It was found that 25°C was the threshold at which reproductive growth stops, while 40°C was the threshold for the cessation of vegetative growth. Additionally, the biological zero for jujube growth had been established at 11°C, and this plant can tolerate low temperatures down to -33°C. Some studies have even reported the plant's ability to withstand temperatures as low as -40°C. In this research, each of the seven studied stations in the region was individually analyzed in terms of maximum temperatures and critical points leading to the cessation of vegetative and reproductive growth.
Conclusion
The findings revealed that the Zirkuh station, with an average annual precipitation of 182.8 mm, received the highest rainfall among the studied stations. Nevertheless, even at this station, jujube plants required supplementary irrigation of 267.2 mm. Fortunately, the region's climatic conditions were characterized by rare and minimal summer rainfall, a phenomenon that could otherwise cause fruit cracking, making this area particularly suitable for jujube cultivation. Analysis of climatic data from 2000 to 2024 demonstrated significant spatial heterogeneity in temperature trends. Modified Mann-Kendall test results indicated a warming trend across all stations, with the most pronounced increase observed in Nehbandan station (3.43°C) and the least in Zirkuh station (0.94°C). These spatial variations can be attributed to altitudinal differences, geographical positioning, and localized microclimatic conditions. Sen's slope estimator corroborated these findings, showing the steepest positive slope in Ferdows station (0.24) and the gentlest in Khosf station (0.03). Linear regression analysis revealed a decadal temperature increase ranging from 0.07°C in Birjand and Zirkuh stations to 2.48°C in Nehbandan station. Statistical analysis of p-values demonstrated significant spatial patterns in temperature changes. While northern and central stations (e.g., Birjand, Boshruyeh, and Ghaen; p ≤ 0.05) show no significant trend, southern stations, particularly Nehbandan (p ≤ 0.02), exhibited statistically significant warming. Regarding precipitation, all stations showed decreasing trends, with a maximum reduction in Nehbandan (-3.32 mm) and a minimum in Birjand (-0.63 mm). Sen's slope analysis indicated the steepest decline in Ferdows (-0.34) and the mildest in Zirkuh (-0.13). Regression analysis estimates an annual precipitation decreased ranging from 0.04 mm/decade in Zirkuh to 1.80 mm/decade in Ghaen. Statistically, northern and central stations (p ≤ 0.05) show significant drying trends, while southern stations like Nehbandan (p = 0.28) exhibited no statistically significant trend.
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