Investigating the feasibility of using Crataegus germanica (L.) Kuntze and .Crataegus monogyna (L.) Jacq. shrubs in bioengineering projects in Hyrcanian forests, Iran: opportunities and challenges

Document Type : Research article

Authors

1 Corresponding author, Prof., Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

2 Ph.D. Student, Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

3 Ph.D, Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

4 Assistant Prof., Department of Mathematics and Statistics, Faculty of Basic Science and Engineering, Gonbad Kavous University, Gonbad Kavous, Iran

Abstract

Background and Objectives: Slope stability in fine-grained forest soils is strongly influenced by the biomechanical characteristics of plant root systems. This study aimed to evaluate and compare the contribution of two native shrub species in the Hyrcanian forests of Iran, medlar (Crataegus germanica (L.) Kuntze) and hawthorn (Crataegus monogyna Jacq.), to soil reinforcement and slope stability. Specifically, the research focused on quantifying root distribution, determining root strength properties, and estimating root-induced additional soil cohesion using the Wu model.
Methodology: The study was conducted in compartment number 118 of the Patom managment district in the Kheyrud Forest Research and Educational Station, North of Iran. A site characterized by an approximate slope of 20%, a southern aspect, and fine-textured soils was selected for the study. To determine the root area ratio (RAR), four representative individuals of each species were selected, and root sampling was performed using the profile wall method on both upslope and downslope sides at three successive 10-cm soil depths. All exposed roots were measured, and RAR values were calculated accordingly. For mechanical tests, 146 intact root samples with diameters ranging from 0.3 to 9.5 mm were collected, and tensile force and tensile strength were measured using a universal testing machine (STM5). Root reinforcement was then estimated by incorporating the Wu model into the Mohr–Coulomb shear strength equation. Statistical analyses were performed using multi-way ANOVA, Bonferroni post hoc tests, and analysis of covariance (ANCOVA).
Results: The results indicated that RAR values significantly decreased with increasing soil depth and distance from the stem, with the highest values observed in the 0–10 cm surface layer. Although the main effect of species on RAR was not significant, the interaction between species and profile wall position was significant, indicating different root distribution patterns between the two species. Mechanical tests showed that tensile force increased with root diameter following a positive power function, whereas tensile strength decreased according to a negative power relationship. Medlar exhibited higher tensile strength than hawthorn, while both species showed similar trends in tensile force increase. Wu model analysis revealed that maximum root-induced additional cohesion occurred in the surface soil layer (0–10 cm) and sharply declined with depth. Moreover, no significant effect of species on the added cohesion to soil was observed.
Conclusions: The results reveal that medlar and hawthorn root systems improve soil reinforcement and slope stability through distinct yet complementary reinforcement mechanisms. Given that the Wu model is more sensitive to root distribution than to root tensile properties, the absence of significant species-level differences in overall soil reinforcement is not unexpected. From a management perspective, the combined use of these two native shrub species is recommended for bioengineering-based slope stabilization projects in the Hyrcanian forests, with hawthorn being particularly suitable for controlling surface erosion and medlar contributing to deeper soil stabilization. Despite their ability to enhance soil shear strength, it should be noted that both medlar and hawthorn are slow-growing native species of the Hyrcanian forests, and their establishment and early growth rates are generally lower than those of fast-growing species. Therefore, their application in bioengineering slope stabilization projects is more appropriate as a long-term preventive strategy rather than as an immediate remedial measure.
 
Keywords: Root density, root mechanical strength, soil reinforcement; Wu model.

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References

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