Assessment of aggregate stability in relation to physiographic characteristics and canopy density in the Zagros Forests, Iran

Document Type : Research article

Authors

1 Ph.D. Student, Department of Forest Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran

2 Corresponding author, Associate Prof., Department of Forest Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran

3 Prof., Department of Forest Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran

4 Assistant Prof., Department of Rangeland and Watershed Management, Faculty of Agriculture, Ilam University, Ilam, Iran

Abstract

Background and Objectives: Soil is one of the most important components of natural ecosystems and has a direct relationship with vegetation cover. Soil aggregate stability is a crucial physical property that plays an essential role in enhancing permeability and preventing soil erosion, key factors for ecosystem health. While much research has focused on chemical and biological properties, physical characteristics like aggregate stability have received less attention. This study investigates soil aggregate stability under the combined effects of canopy cover density, elevation above sea level, and slope aspect, while examining its relationships with soil moisture and organic matter content.
Methodology: The study was conducted in the Zagros forest region (Shalam Mountain), Ilam province, Iran, across various physiographic conditions. A total of 60 soil samples were collected from 0–15 cm depth. Samples came from stands with sparse and semi-dense canopy cover on northern and southern aspects, across three elevation classes (1750–1850, 1850–1950, and 1950–2050 m a.s.l.), using systematic random sampling to assess the interactive effects of canopy cover, slope aspect, and elevation on soil moisture, organic matter, and aggregate stability. Statistical analysis employed three-way ANOVA within a general linear model (GLM) framework. R software and relevant packages were used to analyze correlations among soil organic matter, moisture, and aggregate stability.
Results: Slope aspect and canopy cover density significantly affected (p < 0.05) mean weight diameter (MWD) of soil aggregates, soil moisture, and organic matter. The highest aggregate stability (MWD = 0.69 mm) occurred on northern slopes in semi-dense areas. Similarly, the highest soil moisture (12.46%) and organic matter (6.39%) were recorded in semi-dense, northern-aspect sites, significantly greater than in southern slopes and sparse areas. Significant positive correlations existed between soil moisture, organic matter, and aggregate stability, highlighting their interrelationships in improving soil quality. These findings indicate that higher tree and shrub cover density in this semi-arid region boosts soil moisture, enhancing aggregate stability and reducing erosion. Greater plant cover also reduces surface evaporation, promoting moisture retention, while litter decomposition accumulates organic matter to improve soil structure and stability.
Conclusion: This research shows that sustainable management of Zagros forests, especially preserving tree and shrub canopy cover, plays a key role in preventing soil degradation, maintaining aggregate stability, and sustaining ecosystem health. Reduced canopy density lowers aggregate stability and organic matter, increasing erosion risk. Thus, strategies to enhance vegetation cover and soil aggregate stability are essential for conserving natural resources.
 
 
 

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References

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Iranian Journal of Forest and Poplar Research
Volume 33, Issue 3 - Serial Number 101
January 2026
Pages 191-206

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