Document Type : Research article
Authors
1
Assistant Prof., Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Ahvaz, Iran.
2
Research Expert, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Ahvaz, Iran.
3
Associate Prof. Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Ahvaz, Iran.
4
Expert of the General Directorate of Natural Resources and Watershed Management of Khuzestan province, Ahvaz, Iran.
Abstract
Background and Objectives: The Shisham tree (Dalbergia sissoo Roxb.) is a significant species in the Leguminosae family and Fabaceae subfamily. It is native to regions including Nepal, India, Afghanistan, and Iran. In Iran, it occurs in limited numbers in Khuzestan, Kerman, Sistan and Baluchestan, Bushehr, and Hormozgan provinces. Classified as deciduous, Shisham faces major challenges in dry and semi-dry natural forests, particularly tree dieback due to damaging factors and ecological vulnerabilities. This study investigates the relationship between Shisham tree characteristics and dieback occurrence in the Deyoni region of Dezful County, Iran.
Methodology: This study measured quantitative characteristics of Shisham trees with diameters greater than 7.5 cm, including collar diameter, diameter at breast height, clear stem height, total height, crown area, and crown height. Tree vitality was categorized as healthy or exhibiting dieback. Data normality was assessed using the Kolmogorov-Smirnov test. Spearman and Pearson correlation tests examined relationships between variables, while one-way ANOVA and the Mann-Whitney test analyzed differences between independent and dependent variables.
Results: Average values were 18.6 cm for collar diameter, 14.26 cm for diameter at breast height, 5.82 m for total height, 6.23 m² for crown area, 2.11 m for clear stem height, and 3.7 m for crown height. The Kolmogorov-Smirnov test showed non-normal distributions for collar diameter, diameter at breast height, total height, crown area, and clear stem height, while crown height followed a normal distribution. Spearman correlation revealed a strong relationship between clear stem height and dieback (coefficient = 0.76). No significant relationships emerged between collar diameter, diameter at breast height, or crown height and dieback categories. The Mann-Whitney test confirmed significant differences in clear stem height between healthy and dieback-affected trees. Notably, only clear stem height showed a strong, significant correlation with dieback (0.76), while coefficients for other variables were below 0.5. These results indicate that trees with taller clear stems are more prone to dieback.
Conclusion: The research shows that Shisham trees with greater clear stem height are more susceptible to dieback, influenced by environmental factors like solar radiation and temperature. Trees with smaller crowns exhibit greater drought resistance due to lower water needs. Crown volume and height have minimal impact on dieback, possibly linked to ecological conditions or species traits. These findings improve understanding of Shisham adaptability to environmental stresses and guide water resource management in natural ecosystems. Given the species' importance and extinction risk in Khuzestan Province, further research is needed to identify and manage factors affecting tree health and survival.
Keywords: Dezful, Dieback, Shisham, tree biometric.
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