Effect of single-selection method on soil quality index in the Hyrcanian forests

Document Type : Scientific article

Authors

1 PhD in Forest Soil Science, Department of Silviculture and Forest Ecology, Faculty of Forest Sciences, Gorgan ‎University of Agricultural Sciences and Natural Resources, Gorgan, I. R. Iran

2 Professor, Department of Forest Sciences and Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, I. R. Iran

3 Assistant Professor, Department of Forest Sciences and Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, I. R. Iran

Abstract

Background and Objective: Hyrcanian forests, recognized as one of the most important temperate broadleaf forests of the Northern Hemisphere with a history spanning several million years, play a fundamental role in biodiversity conservation, regulation of ecological cycles, and the provision of ecosystem services. These forests, particularly in their eastern regions, are increasingly exposed to pressures arising from unsustainable harvesting, climate change, and habitat degradation. Among the various components of forest ecosystems, soil serves as the primary substrate for biological and chemical cycles and is therefore central to ecological stability. Soil quality, as an integrated indicator, reflects the soil’s capacity to perform biological, chemical, and physical functions. Accordingly, assessment of the Soil Quality Index (SQI) can provide an effective tool for evaluating the impacts of forest management practices on ecosystem sustainability. The main objective of this study was to investigate the effects of single-tree selection silviculture on soil physical, chemical, and biological properties, as well as on the soil quality index, in the eastern Hyrcanian forests.
Material and Methods: This study was conducted in the Khalilshahr forest area located in eastern Mazandaran Province, northern Iran. The study area comprised two distinct management zones: (1) a forest managed under the single-tree selection system and (2) an unmanaged control area without harvesting. Soil sampling was carried out from the 0–10 cm depth using a completely randomized design in each zone, with a total of 20 soil samples collected per zone. Physical soil properties included texture (percentages of sand, silt, and clay) and bulk density (BD). Chemical properties included pH, electrical conductivity (EC), total nitrogen (TN), phosphorus (P), potassium (K), and organic carbon (OC). Biological properties included ammonium (NH₄⁺) and nitrate (NO₃⁻) production rates, all measured using standard laboratory methods. Principal component analysis (PCA) was applied to identify key indicators, and the soil quality index was calculated using a weighted scoring approach. A generalized linear model (GLM) was employed to determine the main factors influencing SQI.
Results: The results indicated that single-tree selection management significantly improved several soil properties compared with the control area. Specifically, sand content, volumetric soil moisture, pH, EC, total nitrogen, phosphorus, potassium, and ammonium production rate were significantly higher in the managed area (P < 0.05). In contrast, no significant differences were observed in bulk density, organic carbon, or nitrate production rate between the two zones. PCA results showed that the first two components explained more than 67% of the total variance; the first component was associated with soil fertility and physico-chemical quality, while the second component was related to nitrogen cycling processes. The soil quality index was significantly higher in the single-tree selection area than in the control. GLM results revealed that potassium, bulk density, and phosphorus were the most influential variables explaining SQI variation, and the model demonstrated strong predictive performance with a coefficient of determination of 0.87.
Conclusion: The findings demonstrate that single-tree selection forest management, when properly implemented in accordance with sustainable harvesting principles, can positively influence key soil properties and ultimately enhance soil quality. This suggests that selective, tree-based harvesting systems, unlike large-scale clear-cutting, have the capacity to maintain or even improve soil biological and chemical functioning. Given the critical role of soil in forest ecosystem stability and restoration, appropriate soil-focused management can substantially contribute to ecosystem health. Future studies are recommended to investigate the long-term effects of this management approach on soil carbon and nitrogen dynamics, the influence of vegetation species composition, and the role of soil microbial biodiversity. Moreover, the application of advanced modeling approaches to better predict spatial and temporal changes in soil quality indices could support the development of more precise and effective forest management strategies.

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References

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Forest Research and Development
Volume 11, Issue 3
December 2025
Pages 401-420

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