Investigating the occurrence of drought in the forest ecosystem of Zagros due to its coincidence with the decline of oak forests

Document Type : Research Paper

Authors

1 Associate Prof., , Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran Email: dargahian@rifr-ac.ir

2 Prof., Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

3 Assistant Prof., , Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran

Abstract

Background and objectives: Severe droughts and catastrophic floods are major challenges resulting from climate change in the Zagros forest ecosystem. Climatic anomalies such as heat waves and prolonged droughts can create favorable conditions for pest and disease outbreaks, leading to the decline of oak forests. The Zagros oak forests are situated in semi-humid and semi-arid climatic zones and, due to their location in the global dry belt, frequently experience recurrent droughts. The biodiversity and ecological role of these forests, acting as a protective belt and natural barrier, highlight their significance. Spanning 11 provinces and covering an area of 6 million hectares—accounting for 40% of Iran’s forests—the management and planning of this ecosystem is highly complex due to its vast extent and the influence of various environmental factors. Identifying areas that experience more frequent, prolonged, and severe droughts can help forest managers mitigate damage and enhance adaptation to current and future climate changes.
Methodology: To assess drought occurrence in the Zagros ecosystem, the Standardized Precipitation Index (SPI) was utilized to analyze the temporal distribution of drought frequency, duration, and severity over a 28-year period across three selected stations in northern, central, and southern Zagros. Based on regional conditions and classifications from Iran’s National Drought Center, the SPI was categorized into nine classes. The index was calculated for synoptic stations with a 28-year statistical record at 3-, 6-, and 12-month timescales using ClimPACT software. Given the vast study area, the Zagros region was divided into three sections (northern, central, and southern), and drought severity and duration were visualized through graphical representations. After evaluating drought intensity, duration, and frequency across all stations with more than 28 years of data, the percentage of drought-affected areas was calculated for the entire Zagros ecosystem over a common statistical period (1992–2019). The spatial distribution of drought severity during peak drought years was mapped using the ordinary kriging method in ArcGIS software. By identifying years when widespread drought affected the entire Zagros, regions experiencing severe and extreme droughts were classified as critical zones for conservation and research efforts.
Results: The findings indicate no significant difference in drought severity across northern, central, and southern Zagros; however, the timing of the most severe drought events varies. Across all timescales, the longest drought period occurred between 1999 and 2001, coinciding with the onset of forest decline in the Zagros. Notably, from 2007 to 2017, more than 40% of the Zagros region experienced prolonged drought. While droughts can extend over hundreds of kilometers, their intensity and duration are not necessarily uniform across the entire region. Analysis of drought extent from 1992 to 2019 revealed that during certain years, such as 2006 and 2018, no drought events occurred, and the entire Zagros experienced wet conditions. In some years, mild droughts affected less than 10% of the region. However, between 2007 and 2017, more than 40% of the Zagros suffered from prolonged droughts, with certain years, such as 2008, experiencing drought conditions across the entire ecosystem. During this period, in 2010, over 80% of the Zagros region faced drought, and in 2017, this figure exceeded 70%. Notably, before this prolonged dry period, a relatively wet phase lasted for nearly five years.
Conclusion: While multiple factors have contributed to the decline of the Zagros forests, drought has been a primary driver, facilitating the impact of other stressors. The extended duration of droughts has hindered the recovery of trees, while the extreme severity of events—such as the 2008 drought, which affected the entire Zagros—has exacerbated forest decline. Although alternating wet and dry periods are characteristic of the Zagros climate, prolonged drought episodes have heightened ecosystem vulnerability. Severe droughts, when followed by a wet year, tend to have less impact compared to persistent mild droughts. Identifying areas subject to severe and continuous droughts can aid forest managers and policymakers in implementing effective conservation and restoration strategies.

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Main Subjects

References

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History

  • Receive Date: 18 June 2024
  • Revise Date: 29 August 2024
  • Accept Date: 20 October 2024

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