Document Type : Research Paper
Authors
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
10.22059/jrwm.2026.405794.1855
Abstract
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.
Keywords
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