نشریه علمی - پژوهشی مرتع و آبخیزداری

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه احیای مناطق خشک و کوهستانی، دانشکده منابع طبیعی، دانشگاه تهران، کرج، ایران

2 مرکز تحقیقات بین الملل بیابان، دانشکدگان کشاورزی و منابع طبیعی دانشگاه تهران، کرج، ایران

10.22059/jrwm.2026.405794.1855

چکیده

خشکسالی از مهم‌ترین مخاطرات اقلیمی در مناطق خشک و نیمه‌خشک است، افزایش شدت و فراوانی آن در سال‌های اخیر موجب تضعیف کارکرد بوم نظام‌های گیاهی شده است. شواهد میدانی درباره پاسخ پوشش گیاهی درختی مناطق خشک کشور به خشکسالی، به‌ویژه از منظر تغییرات تراکم گیاهی، محدود است. هدف این پژوهش، ارزیابی اثر خشکسالی با شاخص‌های استاندارد SPI و PNPI بر تغییرات تراکم دو گیاهی چگرد (Acacia ehrenbergiana Hayne) و کنار (Ziziphus spina-christi) در دشت اسپکه استان سیستان و بلوچستان بود. همچنین، با نمودارهای تبدیل‌شده شاخص‌های خشکسالی، تأخیر زمانی واکنش تراکم گونه‌ها نسبت به دوره‌های ترسالی و خشکسالی بررسی شد. نتایج نشان داد تفاوت تراکم هر دو گونه در دوره‌های ترسالی و خشکسالی از نظر آماری معنی‌دار است، تغییرات تراکم گیاهی همخوانی بالایی با نمودار تبدیل‌شده شاخص SPI دارد. تحلیل نمودارها بیانگر آن است که واکنش تراکم گیاهی با تأخیری یک تا دو‌ساله پس از وقوع ترسالی و خشکسالی رخ می‌دهد، به‌طوری که کمینه تراکم هر دو گونه یک تا دو سال پس از شدیدترین دوره خشکسالی ثبت شده است. طبق شاخص SPI، ضرایب همبستگی اسپیرمن بین تراکم گیاهی و دوره‌های ترسالی و خشکسالی برای گونه چگرد به ترتیب 62/0 و 96/0 و برای گونه کنار 88/0 و 74/0 به دست آمد. در مقابل، نتایج شاخص PNPI برای گونه چگرد از قابلیت تبیین کمتری برخوردار بود که به تفاوت در ماهیت محاسباتی شاخص‌های مورداستفاده نسبت داده می‌شود. به‌طورکلی، خشکسالی موجب کاهش معنی‌دار تراکم هر دو گونه در منطقه موردمطالعه شد؛ به‌گونه‌ای که تراکم گونه‌های چگرد و کنار به ترتیب از 22/7 ± 33/17 و 51/4 ± 44/8 به 78/4 ± 66/8 و 32/3 ± 11/5 پایه در هکتار کاهش یافت. به‌طورکلی باتوجه‌به آسیب‌پذیری بیشتر گونه کنار نسبت به خشکسالی، تدوین و اجرای راهبردهای مدیریتی مبتنی بر شرایط اقلیمی منطقه برای حفاظت و پایداری این‌گونه ضروری به نظر می‌رسد

کلیدواژه‌ها

عنوان مقاله [English]

Drought-Driven Changes in Tree Density across Dryland Ecosystems of Southeastern Iran

نویسندگان [English]

  • Sirous Shamshiri 1
  • Bijan Azad 1
  • Majid Karimpourrihan 2

1 Department of Rehabilitation of Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran, Karaj, Iran

2 International Desert Research Center (I.D.R.C.) College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

چکیده [English]

Drought is among the most severe climatic hazards in arid and semi-arid regions, and its increasing intensity and frequency in recent decades have substantially impaired the structure and functioning of terrestrial ecosystems. Nevertheless, field-based evidence on drought impacts on woody vegetation in dryland ecosystems, particularly with respect to vegetation density dynamics, remains limited. This study aimed to assess the effects of drought, using the standardized drought indices SPI and PNPI, on density variations of two woody species, Acacia ehrenbergiana Hayne and Ziziphus spina-christi, in the Espakeh Plain, Sistan and Baluchestan Province, Iran. Furthermore, transformed drought index time series were employed to investigate temporal lags in species density responses to wet and dry periods. The results demonstrated that density differences of both species between wet and dry periods were statistically significant, and that vegetation density variations exhibited a strong correspondence with the transformed SPI index. Time-series analysis revealed a lag of one to two years in density responses following wet and drought events, with the lowest densities of both species occurring one to two years after the most severe drought. Based on the SPI index, Spearman correlation coefficients between vegetation density and wet and dry periods were 0.62 and 0.96 for A.ehrenbergiana, and 0.88 and 0.74 for Z.spina-christi, respectively. In contrast, the PNPI index showed limited explanatory power for A.ehrenbergiana, likely due to differences in the computational frameworks of the drought indices applied in this region. Overall, drought resulted in a significant decline in the density of both species in the study area, with A.ehrenbergiana and Z.spina-christi densities decreasing from 17.33±7.22 and 8.44±4.51 to 8.66±4.78 and 5.11±3.32 individuals per hectare, respectively. Given the greater vulnerability of Z.spina-christi to drought stress, the development and implementation of climate-adaptive management strategies are essential to ensure its conservation and long-term persistence.

کلیدواژه‌ها [English]

  • Drought
  • Plant density variation
  • Species vulnerability
  • Standardized Precipitation Index
  • Time-lag response
  • Vegetation dynamics
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