Radial Growth Assessment of Brant’s oak (Quercus brantii Lindl.) and Identification of Pointer Years

Document Type : Complete scientific research article

Authors

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

2 Associate Prof., Forests and Rangelands Research Department, Isfahan Agricultural and Natural Resources Research and Education Center (AREEO), Isfahan, Iran

3 Prof., Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran

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

5 Ph.D. Student, Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran

Abstract

Background and Objectives: Radial growth of trees, recorded in the form of annual rings, is a key indicator for assessing forest dynamics and their responses to environmental and management conditions. Brant’s oak (Quercus brantii Lindl.), the dominant species of the Zagros forests, has experienced considerable growth changes due to human pressures and climatic stresses. However, comprehensive information on the mean radial growth across different sites and regional scales is limited. This study was conducted to estimate the mean radial growth and evaluate the growth patterns of this species in different forest stands of Chaharmahal and Bakhtiari Province, to improve understanding the growth dynamics and identification of pointer years.
Materials and Methods: Sampling was carried out on trees older than middle-aged (almost 50years) in four selected habitats (Tang-e Zendan, Abzalo, Forest Park, and Ghale Madreseh) representing natural forest conditions in the region. From each tree, two perpendicular cores were extracted with increment borer. After preparation with progressively finer sandpaper to clearly distinguish annual rings, ring widths were measured using a LINTAB table. The accuracy of cross-dated time series (growth curves) was verified using TSAP software and the COFECHA program. Mean growth of any trees, sites and finally this area calculated. Given the greater concentration of growth fluctuations during the past two centuries, positive and negative pointer years were identified for each site and the entire region using the Cropper method.
Results: The results showed that growth patterns were similar across all sites, with growth periods of 167 to 313 years. Trees in Tange Zendan and Forest Park exhibited the lowest and highest mean radial growth, with averages growth rate of 0.75 and 1.5 mm, respectively. In terms of age structure, Ghale Madreseh and Abzalo had the oldest and youngest trees, respectively. Analysis of the overall growth curve indicated that the minimum and maximum annual ring widths were 0.31 mm and 2.2 mm, respectively. Considering the greater number of samples after 1880, analysis of growth trends over the past two centuries revealed that maximum and minimum mean growth occurred in 1992 and 2018, reaching 1.85 mm and 0.48 mm, respectively. Pointer year analysis using the Cropper method showed a predominance of negative pointer years across all sites. Regionally synchronous years observed in more than three sites included nine positive years (1924, 1943, 1946, 1957, 1992, 2013, 2016, 2019, 2020) and seven negative years (1901, 1937, 1960, 1964, 1984, 2009, 2018).
Conclusion: This study aimed to estimate the mean radial growth of Q. brantii, a key species of the Zagros forests, which was found to be approximately 1 mm for 170-year-old trees. Growth curves indicated that site dynamics generally follow a regional growth pattern, however, local differences in age structure and environmental conditions influenced ring width variability. Younger sites exhibited faster growth, whereas older stands reflected greater long-term ecosystem stability. The 313-year growth chronology of Brant’ oak in Chaharmahal and Bakhtiari showed a typical pattern of rapid growth in youth, a peak during maturity, and a gradual decline in older ages. Pointer year analysis over the past two centuries demonstrated synchronous regional growth fluctuations, and the predominance of negative years suggests high sensitivity of this species to drought and extreme warming events, potentially threatening the long-term sustainability of Zagros forests.

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Main Subjects

References

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Journal of Wood and Forest Science and Technology
Volume 33, Issue 1
March 2026
Pages 51-69

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