Document Type : Scientific article
Authors
1
Dept. Forest Sciences, Ilam University
2
AssociateProfessor, Research Institute of Forests and Rangelands,Agricultural Research Educationand Extension Organization (AREEO),Tehran, Iran
3
Ph.D. student of Forest Sciences, Department of Forest Sciences, Faculty of Agriculture and Natural Resources, Ilam University, Ilam, Iran
4
Prof., Sari Agriculture Sciences and Natural Resource University, Sari, Mazandaran
5
Assistant Prof., Department of Rangeland and Watershed Management, Faculty of Agriculture, Ilam University
Abstract
Analysis of Releases in the Growth Pattern of Persian Oak (Quercus brantii Lind.) Based on Annual Rings in the Zagros Forest Ecosystem
Background and objectives: Disturbances, as the most important factors in changing natural ecosystems, severely affect the species composition, structure, and function of forests. To better understand tree responses to these disturbances, researchers have employed various techniques. Dendrochronology, due to its ability to provide a long-term perspective, is a unique tool for investigating this issue. Indeed, growth rings provide valuable data on the growth process of trees, which will play an important role in understanding forest dynamics. Using tree chronology is a reliable method, especially for species such as Persian oak (Quercus brantii Lind.), where the ring boundaries in these trees are well distinguished. In this study, growth variations in the annual rings of Persian oak trees in the Zagros forests were analyzed to reconstruct the history of disturbances.
Methodology: This study was conducted in the MelehPunjab Site, 25 km from Ilam city. To this study, a total of 15 wind-fallen trees were sampled in Ilam County. Sampling was done by cross-sections on the stem using a chainsaw. After sample preparation, images of these samples were taken using a camera. Then, these images were transferred to the CooRecorder software environment and the width of the tree rings was measured. Next, for cross-dating of the samples, standardization to remove non-climatic trends from the growth series and creation of chronology, the dplR software package was used in the R software environment. Finally, releases in tree growth patterns were analyzed using the most common method, namely calculating the percentage of growth changes for each series of tree rings, using the TRADER software package in the R. To detect a growth release, the percent growth increase from 10 years before a given year was compared to 10 years after the year of interest.
Results: The analysis of 30 tree-ring series from 15 sampled trees revealed an average series length of 48.16 years. The resulting standard chronology spanned a 72-year period (1951–2022), with key statistical parameters indicating a mean sensitivity of 0.32 and a high expressed population signal (EPS) of 0.88, confirming a strong common climatic signal and sufficient sample depth. Using the TRADER package and the radial-growth averaging technique, a total of 15 growth release events were identified, consisting of 6 major releases (growth increase >50%) and 9 moderate releases (growth increase >25%). Notably, 60% of these releases occurred between 1990 and 2010, a period characterized by recurrent droughts and increased wildfire frequency in the region, indicating a concentrated phase of forest disturbance.
Conclusion: The results of this study demonstrate that climatic events (particularly recurrent droughts) and anthropogenic disturbances (i.e., wildfires) as well as biotic stressors (i.e., pest outbreaks) have significantly influenced growth patterns in oak trees. With the intensification of these drivers in recent decades, the Zagros forests are likely to experience long-term structural changes, including reduced stand density and shifts in species composition. These findings highlight the urgent need for adaptive management strategies, including: 1. Implementing continuous disturbance monitoring through dendrochronological approaches, 2. Scaling up restoration programs in degraded forest areas, and 3. Reducing human-induced stressors that amplify ecosystem vulnerability.
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