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Spatiotemporal monitoring and assessment of green oak leaf-roller outbreaks in Zagros forests using Sentinel-2 data and the BFAST algorithm


Abstract

The decline of oak forests in the Zagros Mountains poses a major threat to the ecological stability and long-term resilience of these ecosystems. This study quantified the effects of green oak leaf-roller (Tortrix viridana L.) outbreaks on canopy dynamics by integrating Sentinel-2 imagery, vegetation indices (NDVI, EVI, NDWI), and the BFAST time-series algorithm. Canopy deterioration was most pronounced at mid-elevations (1200–1800 m) and on moderately sloped terrain (15–30%). The most severe defoliation occurred in 2019 (~ 4253 ha), coinciding with the peak infestation period, followed by partial stabilization in 2021 (~ 1362 ha) and 2022 (~ 1380 ha). Vegetation indices revealed marked physiological stress in affected stands, with NDVI declining to ~ 0.38, EVI to ~ 0.23, and NDWI to ~ 0.1, indicating reductions in photosynthetic activity, canopy density, and crown moisture. Although partial recovery was observed in 2023–2024, persistent biotic pressure limited full canopy regeneration. Time-series modeling showed that spatial and temporal variation in impacted stands was jointly shaped by topography, distance to roads and rivers, drought intensity, and pest activity. The combined use of high-resolution satellite data and BFAST provided an effective framework for detecting subtle canopy degradation and supports more accurate monitoring and adaptive management of pest-induced forest decline.

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Data availability

The Sentinel-2 Level-2A surface reflectance data used in this study are publicly available through the Google Earth Engine (GEE) platform. The GEE processing workflow, including cloud masking (S2cloudless; threshold < 30% with a 200 m buffer), vegetation index calculation (NDVI, EVI, NDWI), and time-series extraction, is openly available in the following public repository: https://github.com/HadiBey-Ourm/OakLeafRoller_GEE A permanently archived version of the repository is available on Zenodo at https://zenodo.org/records/19347108 (https://doi.org/10.5281/zenodo.19347108). The BFAST breakpoint detection analysis was performed externally in R/Python using the exported time-series data. Additional data supporting the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors are grateful to the West Azerbaijan Meteorological Organization for the data provision. Special thanks are also extended to the West Azerbaijan Provincial Department of Natural Resources and Watershed Management for supporting this research project and providing the necessary logistics, financial and expertise in identifying pest-affected areas. The authors also thank Dr. Mohammad Reza Zargaran, faculty member at Urmia University, Iran, for his insightful guidance on oak leaf-roller moth. Furthermore, we would like to express our sincere gratitude to our colleagues and friends for their technical assistance and support in the calculation of the SPEI data.

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This research received no external funding.

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H.B.H. designed the study, collected, analyzed and interpreted the data, and drafted the manuscript. S.A.B. drafted and revised the manuscript. All authors reviewed the manuscript.

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Hadi Beygi Heidarlou.

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Beygi Heidarlou, H., Borz, S.A. Spatiotemporal monitoring and assessment of green oak leaf-roller outbreaks in Zagros forests using Sentinel-2 data and the BFAST algorithm.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-48040-1

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  • DOI: https://doi.org/10.1038/s41598-026-48040-1

Keywords

  • Adaptive pest management
  • Forest health monitoring
  • Pest impacts
  • Remote sensing
  • Time series analysis
  • Vegetation indices
  • Zagros oak forests


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