Assessment of the Recovery of Soil Physical Properties and Ground Vegetation Diversity in Abandoned Skid Trails (Case Study:Hezarjarib Forests-Neka Province)

Background:
In recent decades, excessive and unsustainable logging of forest resources has led to the destruction of many forest ecosystems, resulting in consequences such as erosion, floods, landslides, soil loss, and a reduction in the biosphere's genetic resources. The construction of roads and logging trails has affected and altered physical (soil structure), chemical, and biological properties, soil microbial communities, litter depth, as well as the structure and communities of woody and herbaceous vegetation along the roadsides. In recent years, studies have been conducted on the recovery process of soil properties in skid trails, primarily focusing on surface soil layers and short-term logging histories. However, this research examines the recovery trends of selected soil properties at three sampling depths and the biodiversity of herbaceous cover in abandoned skid trails with long-term logging histories in the forests of the Hazarjarib Neka region (Neka-Zalemrood district).
Materials and methods:
In the present study, four logging trails with ages of 15, 25, 35, and 45 years were selected, and soil sampling was conducted in these trails at three depths (0-10, 10-20, and 20-30 cm) with three repetitions. In this research, characteristics such as bulk density, porosity, moisture content, soil texture, soil aggregate stability indices (including mean weight diameter and geometric mean diameter of aggregates), and organic carbon were measured in the laboratory. Additionally, by recording the frequency of herbaceous species in each sample plot, plant biodiversity was assessed in terms of numerical indices, including species diversity, species richness, and evenness in each of the abandoned logging trails.The presence or absence of significant differences in soil properties related to the skid trail age was determined using a one-way analysis of variance test. Principal component analysis (PCA) was utilized to establish the relationship between different soil characteristics and biodiversity indices within the studied skid trails.
Results:
The results showed that many soil characteristics and indices of diversity and richness differed significantly among different ages of skid trails. The highest values for characteristics such as moisture (44.08, 29.04, 27.47% ), porosity(38.62, 36.18, 32.49%), soil aggregate stability indices (4.66, 4.56, 4.21 mm) were measured in the 45-year-old skid trail across all three soil sampling depths (From right to left in order of depth), while the lowest values moisture (26.19,24.67,22.68%), porosity (30.10, 29.39, 27.75%), soil aggregate stability indices (4.41, 4.30,4.09 mm) were observed in the 15-year-old trail. The results of the analysis of bulk density indicated that the 15-year-old skid trail had the highest value (1.82, 1.89, 1.91g/cm3), while the 45-year-old skid trail had the lowest value (1.60, 1.71, 1.78 g/cm3) for this characteristic. The highest values for Simpson's(0.78) and Shannon-Wiener's diversity indices (1.84) and Margalef's richness index (3.81) were recorded in the 45-year-old skid trail. The results of the principal component analysis also indicated a high correlation between many soil characteristics and biodiversity and richness indices of herbaceous cover in the 45-year-old skid trail.
Conclusion:
According to the results of the present study, the values of many soil properties and biodiversity indices in the 45-year-old skid trails were close to those in the control areas. However, even after 45 years since logging operations, many of these properties still showed significant differences at all three soil sampling depths compared to the control areas. These findings indicate that compacted soils have not fully recovered after 45 years. Therefore, based on the study's results, it is recommended to implement proper skid trail management, adhere to operational guidelines during and after logging activities, and take measures to accelerate the recovery process of skid trails.