The effects of soil disturbance caused by timber skidding operations on the herbaceous vegetation of Hyrcanian forests (case study: Kheyrud educational and research forest)
Document Type : Research Paper
Authors
1 Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
2 Professor, Department of Forestry and Forest Economy, Natural Resources Faculty, University of Tehran
Abstract
Mechanized logging operations are one of the most important disturbance factors in Hyrcanian forests, causing significant physical and biological changes. This study investigates the effect of logging operations on the herbaceous vegetation of the forest floor in the medium term (7 to 20 years since harvest). This study was conducted in the Kheyrud educational-research forest (in two districts; Namkhaneh and Gorazbon) in 2025. Four parcels with different exploitation ages (7, 10, 15 and 20 years since harvest) were selected and in each parcel, sampling plots were established in skid trails with different traffic intensities (low, medium, high and depot) and control (undisturbed) areas. Soil physical properties (bulk density, penetration resistanceand total porosity), litter depth and quality, light intensity and herbaceous vegetation were measured. Simpson, Shannon–Wiener, Evenness (Equitability), and Margalef biodiversity Indices were also calculated. The results showed that soil compaction caused by logging machine traffic significantly increased soil bulk density (up to 62%) and penetration resistance (up to 3 times) and decreased soil total porosity (up to 49%), litter depth and quality. Physical changes in soil and litter, along with a 4-5-fold increase in light received, led to changes in species composition and herbaceous community structure. The herbaceous plants density in skid trails were 3.5 times more than that of control areas, but this increase was due to the dominance of pioneer and light-loving species (such as wavyleaf basketgrass and wood spurge). The results of the biodiversity indices showed that vegetation cover is strongly affected by logging operations (years since harvest and traffic intensity) and that changes in light, litter and soil compaction are key factors in changing the herbaceous vegetation cover of the forest floor. Natural recovery of vegetation at high disturbance intensities is very slow and requires active management interventions.
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