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Article

Mid-Term Evaluation of Herbaceous Cover Restoration on Skid Trails Following Ground-Based Logging in Pure Oriental Beech (Fagus orientalis Lipsky) Stands of the Hyrcanian Forests, Northern Iran

by
Ali Babaei-Ahmadabad
1,
Meghdad Jourgholami
1,
Angela Lo Monaco
2,*,
Rachele Venanzi
2 and
Rodolfo Picchio
2
1
Department of Forestry and Forest Economics, Faculty of Natural Resources, University of Tehran, Karaj 999067, Iran
2
Department of Agricultural and Forest Sciences, University of Tuscia, 01100 Viterbo, Italy
*
Author to whom correspondence should be addressed.
Land 2025, 14(7), 1387; https://doi.org/10.3390/land14071387
Submission received: 4 April 2025 / Revised: 16 June 2025 / Accepted: 24 June 2025 / Published: 1 July 2025
(This article belongs to the Special Issue Vegetation Facing Environmental Changes in Terrestrial Systems: Research, Management and Education)
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Abstract

This study aimed to evaluate the effects of varying traffic intensities, the time since harvesting, and the interaction between these two factors on the restoration of herbaceous cover on skid trails in the Hyrcanian forests, Northern Iran. Three compartments were selected from two districts within the pure oriental beech (Fagus orientalis Lipsky) stands of Kheyrud Forest, where ground-based timber extraction had occurred 5, 10, and 15 years prior. In each compartment, three skid trails representing low, medium, and high traffic intensities were identified. Control plots were established 10 m away from the trails. A total of 54 systematically selected 1 m × 1 m sample plots were surveyed: 27 on skid trails (three traffic intensities × three time intervals × three replicates) and 27 control plots (matching the same variables). Within each quadrat, all herbaceous plants were counted, identified, and recorded. Our findings revealed that only traffic intensity had a clear significant impact on plant abundance. High traffic intensity led to a pronounced decline in herbaceous cover, with disturbed skid trails showing reduced species diversity or the complete disappearance of certain species in comparison to the control plots. Time since harvesting and its interaction with traffic intensity did not yield statistically significant effects. Disturbance led to a reduction in the quantities of certain species or even their disappearance on skid trails in comparison to the control plots. Given the pivotal role of machinery traffic intensity in determining mitigation strategies, there is a critical need for research on region-specific harvesting techniques and the development of adaptive management strategies that minimize ecological impacts by aligning practices with varying levels of traffic intensity.

1. Introduction

The ecological effects of soil disturbances on herbaceous cover in plant communities are multifaceted, involving complex interactions between soil properties, plant–soil feedback, and the responses of herbaceous communities. The long-term consequences of these disturbances, as well as their underlying mechanisms (e.g., soil biotic/abiotic shifts, disturbance intensity, and species-specific plant traits), remain poorly understood due to limited direct evidence. It is also important to note that there is limited direct information on the specific long-term consequences and mechanisms through which soil disturbances influence herbaceous cover in plant communities. Notably, herbaceous plants exhibit short-term impacts distinct from those observed for tree seedlings emerging from a stand, highlighting the need to disentangle transient versus persistent ecological effects [1,2,3,4,5,6,7,8,9,10,11,12,13]. Selective logging in northeastern Oregon, USA, had no significant effects on understory vegetation cover, diversity, or community composition 15 years post-treatment, suggesting resilience in certain ecosystems [14]. In contrast, salvage logging after beetle outbreaks caused short-term shifts in understory communities, increasing species richness (but reducing plant density), favoring graminoids and forbs over shrubs and facilitating exotic invasions [15]. Similarly, in tropical montane rainforests of China, logged forests exhibited reduced functional diversity compared to old-growth stands, underscoring long-term recovery challenges [16]. Previous studies have demonstrated slow understory recovery, with some species failing to reach pre-disturbance levels even after decades [17,18,19,20,21,22,23]. Logging impacts understory plant communities through direct mechanisms (e.g., increased light availability and soil disturbance) and indirect pathways (e.g., altered species composition, reduced phylogenetic diversity, and heightened invasiveness). Canopy removal typically elevates light penetration, favoring light-demanding species while disadvantaging shade-tolerant taxa [24,25,26]. Ground-based operations further disrupt soil structure, damaging the rhizomes of sensitive understory plants and altering nutrient and water dynamics via compaction [24,27]. These combined effects reshape ecological processes, emphasizing the need for disturbance-sensitive logging practices in order to balance resource extraction with biodiversity conservation.
Rubber-tired skidders, commonly used in forestry operations for tree-length-log extraction, have significant impacts on soil, including severe compaction and visible rutting along skid trails [17]. While machinery passes increase bulk density by ~0.17 g cm−3 and compact the upper 10 cm of soil by 62% during initial operations [28,29], natural restoration processes—driven by large-invertebrate activity and organic matter decomposition—can gradually rehabilitate superficial soil layers (≤5 cm depth) after they are disturbed [30]. However, deeper soil recovery from compaction is slow, often spanning decades to a century, depending on factors such as slope, compaction severity, climate, damage extent, and biotic activity (e.g., plant root growth and soil fauna) [3,8,12,13,31,32,33,34]. Without human intervention, full recovery of deeper soil layers may take over 100 years [31,32,33,34], underscoring the need to adopt sustainable logging practices to mitigate long-term ecological degradation. Sustainable forest productivity hinges on soil nutrient preservation, with management practices playing a pivotal role in shaping soil nutrient pools [18]. Vegetation mitigates soil erosion through multiple mechanisms: (1) shielding the surface of the soil from raindrop impacts and runoff; (2) enhancing infiltration and surface roughness, thus reducing runoff velocity; and (3) trapping sediments, thereby minimizing sedimentation [13]. However, logging operations employing heavy machinery often lead to severe soil disturbances and compaction, detrimentally affecting herbaceous cover and plant communities [17,18,19,20,21,22,23]. Studies increasingly highlight the ecological impacts of logging-induced soil compaction on herbaceous cover. For instance, Vennin et al. [9] found that compaction aids disturbance-adapted species (e.g., hygrophilous and nitrophilous taxa) while suppressing forest specialists. Similarly, Closset-Kopp et al. [35] observed that heavy machinery alters plant communities and canopy structure, exacerbating herbaceous cover’s vulnerability to climate change. Light availability has emerged as a critical driver of understory shifts, with skid trails exhibiting higher soil compaction than adjacent forests, promoting the growth of light-demanding and hygrophilous species over shade-tolerant ones. Notably, managed forests subject to selective tree harvesting, such as those in Iran’s Hyrcanian zone, demonstrate greater vascular plant diversity due to increased light availability from reduced stand density and canopy gaps [36]. While compaction initially reduces plant diversity, some studies have reported paradoxical increases in graminoid flora quantities on disturbed trails in comparison to controls [22]. Nevertheless, recovery remains slow, emphasizing the need for practices that balance resource extraction with biodiversity conservation.
Although roads occupy a small proportion of forested landscapes, they act as critical conduits for introducing non-native species into managed stands, altering plant richness and composition across these ecosystems [36,37]. Post-logging operations further disrupt vegetation recovery in harvested areas, with skidder traffic inducing significant alterations to the physical and chemical properties of soil, triggering cascading ecological changes [15,17,18,20,21,38,39]. Consequently, invasive (non-native) species may enter a forest while native plant seeds fail to germinate, as environmental conditions such as soil moisture and light availability influence invasive (non-native) species establishment and contribute to the spread of new species in the area [8,36]. Soil compaction and canopy gaps exacerbate these impacts, creating conditions that favor invasive species establishment (e.g., through shifts in soil moisture and light availability) while suppressing native seed germination [8,36]. Concurrently, soil erosion and nutrient leaching threaten tree regeneration and native herbaceous cover, compounding biodiversity losses [17,40]. Research underscores the dual role of soil disturbances—such as compaction and litter layer disruption—in reshaping herbaceous plant diversity, water cycles, and nutrient dynamics [17,18,19,20,21,22,38,40]. These changes impair key ecosystem functions, including primary productivity and resilience, ultimately degrading overall forest health. Ultimately, soil integrity underpins herbaceous plant abundance along forest roads, emphasizing its foundational role in maintaining ecological balance [41].
The Hyrcanian deciduous broadleaved forests form a vital green belt along the northern slopes of the Alborz Mountains in Northern Iran, stretching south of the Caspian Sea and into the Euro-Siberian region. These forests host unique Arcto-Tertiary relict species, such as Parrotia persica (DC.) C.A. Mey. and Pterocarya fraxinifolia (Michx.) Delchev. [42,43], and were designated a UNESCO World Heritage Site in 2019 due to their exceptional ecological value.
This study investigates the effects of traffic intensity, time since harvest, and their interaction on herbaceous plant cover recovery along skid trails in pure oriental beech (Fagus orientalis Lipsky) stands in the Hyrcanian forests. Additionally, it evaluates the timeframe required for the natural regeneration of herbaceous vegetation following disturbance and degradation caused by logging operations.

2. Materials and Methods

2.1. Study Area

This research was conducted in the Kheyrud Educational and Research Forest, managed by the University of Tehran and located within the Hyrcanian forests. We focused on two districts: Namkhaneh (Compartment 213) and Gorazbon (Compartments 315 and 319). Detailed descriptions of study areas are provided in Table 1.

2.2. Study Method

Based on Forest Management Plan records and expert opinions, skid trails with three levels—low (1–3 passes), medium (3–5 passes), and high (>5 passes)—were identified for each logging interval (15, 10, and 5 years) (Figure 1). In these compartments, trees were felled using selection methods (single trees and groups) and extracted with a Timberjack 450C wheeled cable skidder (empty weight: 10.3 metric tons) (Timberjack Oy, Tampere, Finland). The harvesting system included both short and long logs, which were transported to roadside depots via skidder.
To quantify plant species abundance and diversity, 1 × 1 m quadrats were systematically established. For each traffic intensity class (low, medium, and high), three quadrats were placed at 10 m intervals along skid trails. Parallel control plots were positioned 10 m away from the skid trails laterally. In total, 54 sample plots were surveyed:
  • Twenty-seven skid trail plots: 3 logging intervals × 3 traffic intensities × 3 replicates.
  • Twenty-seven control plots: 3 logging intervals × 3 controls (paired with skid trail intensities) × 3 replicates.
Within each quadrat, all herbaceous plants were identified, counted, and recorded according to species to determine total plant abundance and species richness.

2.3. Data Analysis

Species diversity was assessed using the Shannon–Wiener, Simpson, Dominance, and Equitability indices, which quantify species richness, evenness, and homogeneity in abundance. Vegetation surveys were conducted according to the phytosociological method in July during peak flowering to optimize species identification. Phytosociological syntaxa (plant community classifications) were analyzed to interpret reforestation dynamics and situate vegetation within ecological successional series. The Shannon index and Evenness index were prioritized for evaluating floristic biodiversity, while all indices served to estimate anthropogenic impacts on ecosystem structure. A standard least squares model was used to test the effects of traffic intensity, time since harvest, and their interaction. Main and interactive effects were assessed via p-values, with logarithmic transformations applied to standardize data and stabilize variances for cross-treatment comparisons. In the post hoc comparisons, we used
  • Protected LSD (Least Significant Difference) for mean comparisons;
  • Pairwise t-tests to contrast specific treatment levels.
All analyses were performed in JMP 17.0 (SAS Institute, Cary, NC, USA).

3. Results

In total, from the 54 sampled plots, 25 herbaceous species were collected, including Mentha sp., Drypotris affinis L., Viola odorata L., Mercurialis perennis L., Viola alba Bess., Potentilla reptans L., Lapsana communis, Circaea lutetiana L., Lamium album L., Rubus hyrcanus Juz., Epipactis helleborine (L) Crantz, Euphorbia amygdaloides L., Solanum kieseritzkii C.A. Mey., Scutellaria tournefortii Beneth., Hypericum androsaemum L., Luzula pilosa (Smith) DC., Oplismenus undulatifolius (Ard.), Brachypodium sylvaticum (Hauds.), Sanicula europaea L., Epimedium pinnatum L., Poa sp., Mentha aquatic L., and Geranium sp.
The highest abundance was recorded for Viola alba (366 individuals), followed by Euphorbia amygdaloides (269), Asperula odorata (196), Carex pendula (102), and Mercurialis perennis (96), as shown in Table 2. These species dominated the herbaceous layer, reflecting their adaptability to post-disturbance conditions in the studied forest stands.
A total of 1405 herbaceous individuals, representing 18 families, were recorded across the study area. Species identity and family affiliation are critical for assessing the severity of the ecological impact of logging and skidding operations on skid trails. Details on family abundance are provided below:
  • Violaceae dominated, with 430 specimens (e.g., Viola alba).
  • Euphorbiaceae (e.g., Euphorbia amygdaloides) and Rubiaceae (e.g., Asperula odorata) followed, with 269 and 196 individuals, respectively.
Cyperaceae (e.g., Carex pendula) and Rosaceae exhibited lower abundances. A total of 658 herbaceous individuals were recorded on skid trails, whereas 747 individuals were recorded in the control plots (Table 3), reflecting distinct ecological responses to disturbance gradients. Some species were found only in the control plots, such as Brachypodium sylvaticum, Epimedium pinnatum, Luzula pilosa, and Oplismenus undulatifolius, while specimens of Circaea lutetiana, Epipactis helleborine, Geranium sp., Lapsana communis, and Poa sp. Scutellaria tournefortii e Viola odorata L. were found only on the skid trails.
Statistical analysis revealed significant differences (α = 0.05) in herbaceous species composition between the skid trails (across traffic intensities) and control plots, with 18 of 25 species exhibiting distinct responses. Notably, three dominant taxa—forest understory species, sedges (Cyperaceae), and Mercurialis perennis—showed significant interactions between traffic intensity and time since logging (Table 4), highlighting the role of skidding operations in shaping post-disturbance vegetation dynamics.
Statistical analysis of herbaceous species regeneration revealed that the interaction between time since harvest and traffic intensity was largely non-significant across compartments and traffic levels. A single exception occurred in Compartment 213 (15 years post-harvest, with low traffic intensity), where a significant interaction was detected (α = 0.05).
Statistical analyses were conducted to assess the regeneration of herbaceous species influenced by traffic intensity (low, medium, and high) and time since harvest, focusing on the five most abundant species among the twenty-five studied. For each compartment, comparisons were made between skid trails (categorized by traffic intensity) and their corresponding control plots (matched by traffic intensity level) (Table 5 and Figure 2).
According to the results of the independent t-test, 21 out of 45 results were significant. In 5 cases, no results were obtained due to the absence of Carex and Mercurialis annua species in some sampled plots, and in 19 cases, the results were not significant (Table 5 and Figure 2).
The analysis of interactions between traffic intensity and time since harvest revealed that skidding operations significantly altered plant abundance across species. These findings were found to be consistent when evaluating traffic intensity and time since harvest independently. A significant interaction between traffic intensity and time since harvest was observed only when comparing 5-year-old skid trails with those 10 years old (* p = 0.03 *). No significant interactions were detected in other pairwise comparisons. In low-traffic skid trails that were 10 and 15 years old, time since harvest significantly influenced herbaceous cover regeneration (* p = 0.04 *), suggesting gradual recovery in minimally disturbed areas over time. In the species examination, it was also revealed that the regeneration of some species was influenced by traffic intensity, such as Viola odorata (p = 0.06), Euphorbia amygdaloides (p = 0.00), and Circaea lutetiana (p = 0.00), and some species were affected by time since harvest, such as Asperula odorata (p = 0.04), Potentilla reptans (p = 0.01), Hypericum androsaemum (p = 0.01), Poa sp. (p = 0.00), and Mentha aquatica (p = 0.00). In terms of the interaction effect of time since harvest and traffic intensity, species such as Circaea lutetiana (p = 0.00), Hypericum androsaemum (p = 0.02), Oplismenus undulatifolius (p = 0.04), Poa sp. (p = 0.00), and Mentha aquatica (p = 0.00) were identified.

3.1. Number of Plants and Traffic Intensity

A central aim of this study was to assess whether the examined treatments (and their interactions) influenced herbaceous plant abundance. Statistical analyses of logging impacts revealed that traffic intensity significantly affected plant regeneration, particularly in high-traffic areas. Specifically, high traffic intensity exerted the most pronounced negative effect on herbaceous cover recovery on skid trails, suppressing regeneration even years post-disturbance (Table 6). This underscores the critical role of traffic regulation in mitigating long-term ecological degradation (Table 6).

3.2. Number of Species and Traffic Intensity

The results of statistical analyses on the number of species established after skidding operations under varying traffic intensity levels revealed that traffic intensity significantly affected species establishment (p < 0.001). Additionally, some species failed to regenerate on skid trails following logging. The results of the analyses of time since harvest and the interaction between traffic intensity and time since harvest indicated—at a 95% confidence level—that skidding operations had no significant impact on species regeneration.
To assess the impact of traffic intensity levels, time since harvest, and their interaction on species diversity, Shannon, Simpson, Dominance, and Equitability diversity indices were calculated. The results revealed that, on average, the diversity indices under the influence of low traffic intensity (with a 15-year post-harvest period) exhibited higher values compared to those in the control plots. Conversely, under the influence of medium and high traffic intensity (also with a 15-year post-harvest period), the control plots showed higher diversity values than skid trails. This highlights the combined influence of traffic intensity and time since harvest on species diversity metrics. For the 10-year post-harvest period, analyses considering the influence of high and medium traffic intensity demonstrated that these levels significantly reduced species diversity indices and negatively affected herbaceous plant cover regeneration. In contrast, low traffic intensity showed no substantial impact during this period. For the 5-year post-harvest period, comparisons of high, medium, and low traffic intensity revealed no noticeable differences in species diversity indices between the control plots and skid trails.

4. Discussion

Logging-induced soil compaction increased functional and phylogenetic dispersion in understory plant communities. This effect was particularly evident in functional response traits, which directly mediate the relationship between disturbance and shifts in plant community composition [14,15,16,25,26,27,44].
Forest harvesting can significantly alter the species composition and diversity of understory plant communities. For example, heavy forestry vehicles have been shown to increase the abundance of pioneer species and light-demanding plants and reduce late-successional species [45,46]. This shift often results in homogenized plant communities dominated by a limited number of species [46]. Furthermore, logging operations involving heavy machinery can disrupt the functional traits and evolutionary relatedness (phylogenetic structures) of understory plant communities. Increased forest harvesting intensity can drive the formation of functionally and phylogenetically dispersed community structures, reflecting a shift toward species with better adaptations for exploiting disturbed environmental conditions [47,48]. Such disturbances also heighten forests’ vulnerability to invasions by non-native species. However, the presence of resprouting canopy trees can counteract this vulnerability by rapidly re-establishing canopy cover and limiting resource availability for invasive species [26]. Synchronic studies indicate that mechanized logging often increases understory plant diversity, primarily benefiting disturbance-adapted species such as grasses, ruderals, and invasives, with soil compaction and wheel tracks favoring light- and moisture-demanding taxa [19,22,49,50,51,52]. In contrast, diachronic studies remain scarce and typically rely on indirect proxies like canopy changes rather than direct field assessments of mechanization impacts. While research such as the study by Closset-Kopp et al. [35] links heavy forestry vehicles to vegetation shifts, causal evidence connecting specific mechanization traces (e.g., skid trails) to long-term ecological changes is lacking, underscoring a critical gap in our understanding of forestry’s legacy effects.
The study area exhibited relatively high species diversity, with 25 herbaceous species from 18 plant families identified across skid trails and control plots in the three examined compartments. The site had a history of timber extraction conducted at varying intervals (5, 10, and 15 years post-harvest) and was analyzed under three levels of pre-existing traffic intensity per compartment, with no additional machinery traffic during the study. The results demonstrated that traffic intensity alone significantly reduced vegetation recovery, species richness, and diversity indices in the skid trails in comparison to the control plots. Notably, skidder activity—regardless of the time that had elapsed since logging—directly influenced vegetation recovery, species composition, and diversity metrics. These findings align with prior research by Demir et al. [40], Jourgholami et al. [53], and Karamirad et al. [41]. Furthermore, in tropical montane rain forests in China, Ding et al. [16] found that logged forests still need more time to recover the levels of functional diversity observed in old-growth forests, indicating the long-term consequences of logging on plant communities.
In this study, traffic intensity, associated with selective and group-selection logging methods in Northern Iran’s forests, was lower in terms of frequency and severity of disturbance than in regions or countries where clear-cutting is standard practice. Nevertheless, even this moderate traffic level induced measurable disturbances in herbaceous vegetation recovery, reducing species diversity indices and plant richness in skid trails relative to the control plots. Over time, however, natural regenerative processes have allowed skid trails to gradually recover in terms of species richness and diversity metrics.

4.1. Number of Plants

The results indicated that vegetation recovery in the study area—measured by species richness—was not significantly influenced by the post-harvest period (i.e., the time that has elapsed since logging). However, when comparing 15-year-old skid trails to the control plots, more pronounced traffic intensity effects were observed. At the 90% confidence level, logging operations significantly affected herbaceous vegetation recovery. Furthermore, comparisons between the 5- and 10-year post-logging periods revealed statistically significant differences in recovery rates (p = 0.03). These findings align with studies by Buckley et al. [19]. Under the environmental conditions of Iran’s Hyrcanian forests, this pattern may stem from alterations in canopy cover, which modulates light availability and the penetration of rainfall onto the forest floor on skid trails. Also, Vennin et al. [9] demonstrated that canopy openings (natural or management-induced) drive vegetation shifts by promoting the growth of light-demanding species and tree regeneration. The findings of this study contradict those of Makineci et al. [17], who reported that “undisturbed areas exhibited significantly greater herbaceous cover than skidder-affected areas.” This inconsistency may arise from divergent environmental conditions, such as variations in rainfall regimes, soil composition, or forest structure between the study regions. Thinning not only directly impacts seedlings but also alters microclimatic conditions (e.g., solar radiation, air and soil temperature, rainfall, humidity, and soil moisture), which subsequently influence understory regeneration [54]. The extent of these changes depends on stand age and canopy density: denser canopies undergo more significant microclimatic shifts after interventions like thinning or clearing, driven by reductions in leaf area and canopy openness. These environmental modifications reshape growing conditions for understory species [9,22,36,54].
Plant species with competitive traits, such as rapid growth rates and lower water/nutrient demands under stress conditions [40], tend to dominate in disturbed ecosystems. While soil damage, compaction, and structural disruption are key drivers of reduced herbaceous cover, other factors like soil moisture, nutrient availability, light accessibility, interspecific competition, allelopathy, and species-specific life cycles may counteract or diminish the impacts of skidding intensity. These findings align with the results of the studies by Demir et al. [40] and Jahani [55]. Skid trail recovery dynamics are strongly tied to traffic intensity in the years following logging. Certain species display enhanced germination rates immediately post-logging due to soil surface disturbance, while others re-emerge as environmental conditions gradually stabilize toward pre-logging states. A 32-year study (1990–2022) on broadleaved forests of Northeastern France revealed that vegetation changes were primarily driven by mechanization (e.g., wheel tracks, skid trails, etc.) and canopy openings rather than climate change. Soil compaction from forestry vehicles increased non-forest, hygrophilous, and nitrophilous species numbers, while the thermophilization of plant communities (+0.27 °C via bioindication) lagged far behind recorded temperature rises (+1.5 °C) [9].

4.2. Number of Species

Analyses of the interaction between traffic intensity and post-harvest period revealed that, except in Compartment 213 (which had low traffic intensity), these factors had no statistically significant impact on herbaceous cover regeneration at the 95% confidence level. This outcome aligns with the findings of Lotfalian et al. [56] and Demir et al. [40] but contradicts those reported by Demir et al. [38], who identified disturbance as a key driver of reduced herbaceous cover. In the study area, species richness remained largely unaffected by logging operations or skidder traffic. This resilience may stem from adaptations of local species to the region’s soil characteristics and the infrequency of high-intensity traffic events.
The present study reveals that for five abundant herbaceous species—Viola alba Bess., Euphorbia amygdaloides L., Asperula odorata L., Carex pendula L., and Mercurialis perennis L.—the interaction between traffic intensity and time since harvest did not show significant differences when compared to the control plots. This finding aligns with the research conducted by, Demir et al. [40], and Vennin et al. [9]. However, for twenty less abundant herbaceous species, the results were statistically significant, except for three species (Potentilla reptans L., Sanicula europaea L., and Solanum kieseritzkii C.A. Mey.). In other words, the interaction between traffic intensity and time since harvest had a significant effect on the recovery of vegetation on skid trails in comparison to the control plots. This can be attributed to changes in soil structure, compaction, moisture levels, and soil disturbance for these species.
Comparisons of traffic intensity–post-harvest period interactions with adjacent control plots revealed statistically significant effects only in Compartment 213, characterized by a 15-year post-harvest period and low traffic intensity. Analysis of individual herbaceous species on skid trails revealed that logging operations significantly impacted the abundance of the top five most abundant species in 21 out of 45 trails. In contrast, nineteen trails showed no detectable effects, and five trails exhibited no response due to the absence of target species in the sampled areas. Notably, Viola alba Bess. displayed sensitivity to logging in four trails. The effect of traffic intensity on species richness on skid trails (compared to control plots) was statistically significant, contradicting Lotfalian et al.’s findings [56] but aligning with the results reported by Litschert and MacDonald [29]. This discrepancy may stem from species-specific sensitivities to reduced soil moisture, physical disturbance or compaction, and competitive exclusion by fast-growing dominant species, which outcompete slower-growing plants for light and moisture.
Statistical analyses of the post-harvest period and its interaction with traffic intensity did not reveal any statistically significant effects on the measured outcomes. These findings are consistent with studies by Lee et al. [57] and Ghasemi Aghbash et al. [58] but contradict the findings reported by of Salehi et al. [59] and Zeng et al. [60]. This divergence may reflect ecological equilibrium dynamics, where species richness on skid trails stabilizes over extended post-logging periods, diminishing detectable differences between disturbed and undisturbed areas. Analysis of species diversity indices (Shannon, Simpson, Dominance, and Equitability) revealed no statistically significant effects from skidding operations when comparing control plots to skid trails across varying traffic intensity levels and post-harvest periods (p > 0.05 at the 95% confidence level). These results suggest that skidding activities, under the studied conditions, did not induce measurable shifts in species diversity metrics within the examined forest compartments. While comparisons of biodiversity and evenness indices between skid trails and control plots showed no statistically significant differences, a notable trend emerged: species diversity on skid trails frequently exhibited non-significant directional shifts relative to the control plots within the same study area, with few exceptions. Through treatment-specific analyses, it became evident that traffic intensity and post-harvest period can drive subtle yet observable alterations in species diversity patterns, even in the absence of statistical significance. Vennin et al. [9] concluded that forest management and mechanization in forests in Amance impact understory vegetation through multiple pathways, including physical disruption (e.g., plant destruction), soil degradation (hydrology, compaction, and nutrient shifts), altered light regimes, microclimate shifts, and species introductions (e.g., the arrival of invasive or vehicle-dispersed species) [9,61,62,63]. These factors collectively alter habitat conditions, favoring disturbance-adapted taxa while threatening forest specialists.
The inverse Simpson index serves as a measure of species evenness, with values approaching 0 indicating low evenness (dominance by a few species) and values near 1 reflecting high evenness (a balanced species distribution) [64]. Detailed analysis of post-harvest periods revealed nuanced trends:
  • In the 5-year post-harvest period: The Simpson index indicated greater evenness on six skid trail plots in comparison to that for the control plots.
  • In the 10-year post-harvest period: No significant differences in evenness were observed between skid trails and controls.
  • In the 15-year post-harvest period: Skid trail plots exhibited higher evenness than the control plots, suggesting gradual recovery toward pre-disturbance conditions.
The Shannon index, a measure of ecological community stability and diversity, theoretically ranges from 0 (low diversity) to 4.5, with values rarely exceeding 5 in practice [64]. Margalef [65] further contextualized its application, noting typical values between 1.5 and 3.5 for natural communities. This index quantifies diversity using principles from information entropy theory, where higher values reflect greater species richness and evenness. The Shannon index equals zero in two scenarios: (1) when only a single species is present in the sampled community or (2) when the community has undergone severe ecological degradation. Conversely, the index reaches its maximum value when all species exhibit equal abundance—a state reflecting minimal environmental stress and optimal ecological balance. Thus, lower Shannon index values directly correlate with higher levels of ecological degradation in the studied community.
The results of this study demonstrate that the control plots consistently exhibited higher Shannon index values compared to the skid trail plots. This disparity underscores the negative impact of ground-based skidding operations on species diversity, with herbaceous communities in skid trails showing reduced species richness post-disturbance. These patterns suggest a shift toward fast-growing, opportunistic species at the expense of native flora, a trend corroborated by Zeng et al. [60], Litschert and MacDonald [29], and Vennin et al. [9]. The Equitability index, which reflects the evenness of the studied community, shows the distribution of individuals among species. A higher value indicates that species have more equal numbers, while a lower value suggests an imbalance. In this study, in contrast with the findings of Makineci et al. [17], there was no significant difference between the skid trails and control plots.
The Dominance index, which quantifies the degree to which one or a few species dominate a community, was analyzed to assess competitive dynamics among plants. This index ranges from 0 (no dominance or competition) to 1 (complete dominance by a single species). A value near zero implies balanced coexistence with no species exerting competitive superiority, while higher values reflect stronger dominance. In this study, traffic intensity and post-harvest period exhibited no statistically significant influence on species dominance or competitive interactions, as measured by the Dominance index. This suggests that neither skidding operations nor time since logging altered the proportional abundance of dominant vs. subordinate species in the examined communities. Notably, the low Dominance index values observed across plots indicate minimal interspecific and intraspecific competition, implying a community structure where resources are not monopolized by dominant species. The relationship between logging intensity and understory plant diversity in forest ecosystems is shaped by a complex interplay of factors, including functional trait composition, phylogenetic relatedness, resource availability, and habitat heterogeneity. While logging can alter the functional diversity and phylogenetic structure of understory communities, its long-term impacts on vegetation resilience and biodiversity remain context-dependent, influenced by the following factors:
  • Soil recovery dynamics: Post-logging soil compaction and nutrient cycling shifts.
  • Light-regime changes: Altered canopy cover affecting shade-tolerant vs. pioneer species.
  • Species interactions: Competitive exclusion, facilitation, or recruitment limitations.
These dynamics underscore the need for further research to unravel the following:
  • The temporal scales of recovery: How decades-long successional processes mediate diversity trajectories.
  • Scale-dependent responses: Variations in species richness and community assembly across spatial gradients (e.g., microsites vs. landscape-level impacts).
  • Mechanistic drivers: Genetic, functional, and environmental filters shaping post-logging recolonization.
Individual species reactions reflected their ecological strategies and functional traits. Shade-tolerant herbs with clonal propagation (e.g., Mercurialis perennis) demonstrated resilience to moderate disturbance, likely due to their vegetative regrowth capabilities. In contrast, slow-growing species reliant on seed dispersal (e.g., Viola spp.) declined sharply under high traffic, suggesting limited adaptability to soil compaction and physical disruption. Factors such as root depth, dispersal mode, and stress tolerance likely mediated these divergent recovery pathways.
Traffic intensity alone had a significant impact on plant abundance. High traffic intensity induced a pronounced decline in herbaceous cover. Accordingly, Vennin et al. [9] highlighted the need to prioritize minimizing mechanization impacts on plant communities in forestry planning as harvester use increases in temperate deciduous forests.
To address knowledge gaps and refine sustainable forest management practices, the following research directions should be prioritized based on the findings of this study: investigate how traits like resprouting capacity or shade tolerance mediate species’ resilience to skidding, assess how warming temperatures or altered rainfall patterns may exacerbate or mitigate skidding impacts, and quantify the long-term costs of biodiversity loss against short-term logging efficiency gains.
While pre- and post-harvest soil compaction data were not systematically collected in this study, prior research (e.g., Jourgholami et al. [66,67]) has demonstrated that repeated skid trail use significantly increases soil compaction and penetration resistance, which correlate with reduced root elongation and delayed regeneration of understory vegetation. Future studies should prioritize longitudinal soil monitoring to disentangle the direct effects of compaction from other biotic and abiotic factors influencing vegetation recovery.
A key limitation of this study is the restricted number of replicates (n = 3 per treatment), which reflects the logistical challenges of conducting field experiments on the remote, steep terrain of the Hyrcanian forests. While this sample size is consistent with the sizes used in similar skid trail recovery studies, it may constrain the statistical power for detecting subtle ecological interactions, particularly between traffic intensity and time since harvest. To mitigate this, we employed systematic sampling across multiple compartments (5-, 10-, and 15-year intervals) and rigorous statistical transformations to enhance data robustness. Notably, our results still revealed significant effects of traffic intensity on herbaceous cover, a finding that aligns with the broader literature on soil compaction and vegetation recovery. However, the non-significance of time-since-harvest effects could partly stem from limited replication or the relatively short recovery window (≤15 years) in these slowly regenerating beech stands. Future studies should prioritize the use of larger-scale, longitudinal designs to disentangle these temporal dynamics. Despite these constraints, our work provides actionable insights for forest managers: high traffic intensities consistently degraded herbaceous diversity, underscoring the need for region-specific mitigation strategies, such as limiting skidder passes or adopting alternative extraction methods in sensitive zones.

5. Conclusions

In this study, we assessed the recovery and restoration of herbaceous vegetation on the forest floor by examining two key aspects: plant abundance and species diversity. Our analysis compared skid trails affected by logging and skidding operations with undisturbed control areas. We investigated the influence of traffic intensity, time since harvest, and their interaction on vegetation recovery. Our findings revealed that only traffic intensity had a clear significant impact on plant abundance. In detail, areas subjected to high levels of traffic exhibited a notable decline in herbaceous cover. However, for time since harvest and the interaction between traffic intensity and time since harvest, the results were not statistically significant in terms of vegetation recovery on skid trails. Despite this lack of significance at the 95% confidence level, both time since harvest and the interaction between this factor and traffic intensity influenced the recovery of herbaceous vegetation at lower confidence levels in 5-, 10-, and 15-year time-since-harvest intervals.
In terms of species counts, the impact of skidding operations was found to be significant across all traffic levels, showing that skidding operations influenced vegetation recovery. However, the majority of the results concerning species counts were not significantly affected by different traffic levels or time since harvest. The Shannon, Simpson, Dominance, and Equitability indices indicated that species diversity and evenness in species recovery varied across skid trails with different times since harvest and traffic intensities. These factors influenced species diversity and evenness, but the Dominance index suggested there was no significant interspecific or intraspecific competition. Although the differences in the Shannon, Simpson, and Equitability indices were not statistically significant, a closer analysis of the results indicates that logging operations caused varying degrees of damage and degradation to species diversity and evenness. This disturbance led to a reduction in the quantities of certain species on skid trails compared to the control plots or even their disappearance.
To mitigate these impacts, management strategies should prioritize traffic intensity as a key variable:
  • Low-traffic areas: Limit machinery use to designated paths, and enforce seasonal restrictions (e.g., avoiding wet periods) to minimize soil compaction. Promote natural recovery by protecting resilient species (e.g., clonal herbs).
  • Medium-high-traffic areas: Prioritize the planting of species with high stress tolerance (e.g., deep-rooted perennials). Use brush mats or slash layers on skid trails to reduce direct soil impact.
  • High traffic zones: Consider permanent trail closure after repeated use, coupled with active restoration (e.g., reseeding with native, disturbance-adapted species).
Adaptive harvesting methods, such as spatially restricting machinery to fixed corridors, employing cable logging in sensitive areas, or adopting lighter equipment, could further reduce ecological damage. Future research should evaluate species-specific trait responses (e.g., root architecture, dispersal mechanisms, etc.) to tailor restoration efforts and refine harvesting protocols based on disturbance thresholds. Based on the findings of this study, we recommend adopting the following management strategies to mitigate logging impacts and enhance ecosystem recovery in temperate forests like those in the Hyrcanian region:
  • Long-term monitoring: Track post-logging recovery beyond 15 years to assess resilience thresholds.
  • Scale-dependent planning: Address microsite variability (e.g., light, soil compaction, etc.) to aid species recolonization.

Author Contributions

Conceptualization, A.B.-A., M.J., A.L.M. and R.P.; methodology, A.B.-A. and M.J.; software, A.B.-A.; validation, M.J., A.L.M., R.V. and R.P.; formal analysis, M.J., A.L.M. and R.V.; investigation, A.B.-A. and M.J.; writing—original draft preparation, A.B.-A., M.J., A.L.M., R.V. and R.P.; writing—review and editing, M.J., A.L.M., R.V. and R.P.; visualization, A.B.-A. and M.J.; supervision, A.L.M. and M.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are available from the corresponding author upon reasonable request.

Acknowledgments

This work was supported by the Italian Ministry for Education, University, and Research (MIUR) for financial support (Law 232/2016, Italian University Departments of Excellence 2023\u20132027) project\u201C Digitali, Intelligenti, Verdi e Sostenibili (D.I.Ver.So)\u2014UNITUSDAFNE WP3\u201D). Also, the authors would like to acknowledge the constructive and valuable comments provided by the editor and four anonymous reviewers, which greatly helped us to improve the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Land 14 01387 g001
Figure 1. Study area and plot design for vegetation sampling in a quadrat.
Figure 1. Study area and plot design for vegetation sampling in a quadrat.
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Figure 2. Average values with standard deviations of the quantities of plants for plots categorized for every time since harvest and traffic intensity on skid trails with respect to herbaceous species.
Figure 2. Average values with standard deviations of the quantities of plants for plots categorized for every time since harvest and traffic intensity on skid trails with respect to herbaceous species.
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Table 1. Descriptions of study areas.
Table 1. Descriptions of study areas.
Compartment No.213315319
DistrictNamkhanehGorazbonGorazbon
Time since harvest (years)15510
Forest typeBeech–hornbeamBeech–hornbeamBeech–hornbeam
Elevation (meters above sea level)98011951230
Average annual rainfall (mm)108113801380
Soil typeAlfisol, classified as washed-brown forest soil with a loam–clay loam texture and a depth of 100 cmAlfisolInceptisol with a depth of 145 cm
Main herbaceous plant speciesBlackberry, holly, Asperula, spurge, violet, grasses, and clematisBlackberry, holly, Asperula, Sanicula, male fern, mercury grass, spurge, and grassesBlackberry and spurge, holly, Asperula, Sanicula, violet, and male ferns
General aspectWest to southwestSouth to southwestNorth and south
Slope (%)282522
Area (ha)34.720.0342.74
Table 2. Floristic list, chorology, and growth forms of herbaceous plants in Compartments 213, 315, and 319 of Kheyrud Forest.
Table 2. Floristic list, chorology, and growth forms of herbaceous plants in Compartments 213, 315, and 319 of Kheyrud Forest.
Scientific NameFamilyBiological FormChorotypeGrowth FormNumber
Asperula odorata L.RubiaceaeGeoPLBroadleaf herbaceous196
Brachypodium sylvaticum (Huds)GramineaeHemPLGrass17
Carex pendula L.CyperaceaeGeoESGrass102
Circaea lutetiana L.OnagraceaeGeoES, IT, MBroadleaf herbaceous4
Drypotris affines L.AspidiaceaeGeoESFern39
Epimedium pinnatum L.PodophyllaceaeGeoHyrBroadleaf herbaceous2
Epipactis helleborine (L) CrantzOrchidaceaeGeoPLBroadleaf herbaceous2
Euphorbia amygdaloides L.EuphorbiaceaeGeoESBroadleaf herbaceous269
Geranium sp.GeraniaceaeHemESBroadleaf herbaceous1
Hypericum androsaemum L.HypericaceaeChaESBroadleaf herbaceous41
Lamium album L.Lamiaceae/labiataeHemE, ITBroadleaf herbaceous23
Lapsana communis L.Asteraceae-CompositaeThE, ITBroadleaf herbaceous2
Luzula pilosa (Smith) DC.JuncaceaeGeoES, MGrass5
Menta aquatic L.Lamiaceae/labiataeHemITBroadleaf herbaceous1
Mentha sp.Lamiaceae/labiataeHemITBroadleaf herbaceous24
Mercurialis perennis L.EuphorbiaceaeGeoES, MBroadleaf herbaceous96
Oplismenus undulatifolius (Ard)GramineaeHemES, MGrass20
Poa sp.GramineaeThES, ITGrass7
Potentilla reptans L.RosaceaeHemES, ITBroadleaf herbaceous52
Rubus hyrcanus Juz.RosaceaePhESBroadleaf herbaceous33
Sanicula europaea L.UmbelliferaeHemPLBroadleaf herbaceous5
Scutellaria tournefortii Beneth.Lamiaceae/labiataeThITBroadleaf herbaceous4
Solanum kieseritzkii C.A. Mey.SolanaceaeChaESBroadleaf herbaceous30
Viola alba Bess.ViolaceaeHemESBroadleaf herbaceous366
Viola odorata L.ViolaceaeHemES-MBroadleaf herbaceous64
Growth forms: Cha = chamaephyte, Geo = geophyte, Hem = hemicryptophyte, Ph = phanerophyte, Th = therophyte. Chorotypes: ES = Euro-Siberian; Hyr = Hyrcanian; IT = Irano-Turanian; M = Mediterranean; PL = pluriregional, E = endemic.
Table 3. Quantities and percentages of herbaceous species classified according to skid trail and control (n = 54, α = 0.05).
Table 3. Quantities and percentages of herbaceous species classified according to skid trail and control (n = 54, α = 0.05).
SpeciesSkid TrailSkid Trail PercentageControlControl Percentage
Asperula odorata L.13468.376231.63
Brachypodium sylvaticum (Huds)0017100
Carex pendula L.6866.673433.33
Circaea lutetiana L.410000
Drypotris affines L.1230.772769.23
Epimedium pinnatum L.002100
Epipactis helleborine (L) Crantz210000
Euphorbia amygdaloides L.8631.9718368.03
Geranium sp.210000
Hypericum androsaemum L.717.073482.93
Lamium album L.626.091773.91
Lapsana communis L.210000
Luzula pilosa (Smith) DC005100
Menta aquatica L.210000
Mentha sp.1562.5937.5
Mercurialis perennis L.24257275
Oplismenus undulatifolius (Ard)0020100
Poa sp.710000
Potentilla reptans L.3363.461936.54
Rubus hyrcanus Juz.515.152884.85
Sanicula europaea L.120480
Scutellaria tournefortii Beneth.410000
Solanum kieseritzkii C.A. Mey.15501550
Viola alba Bess.16545.0820154.92
Viola odorata L.6410000
Total65646.6974953.31
Note: The species found only on skid trails or in control plots are in bold.
Table 4. Results of an independent t-test on the interaction effect of traffic intensity and time since harvest between skid trail (S-T) and control (C) areas in the presence of herbaceous species (n = 54, α = 0.05; average ± standard deviation). * indicates significance; n.s indicates no significance.
Table 4. Results of an independent t-test on the interaction effect of traffic intensity and time since harvest between skid trail (S-T) and control (C) areas in the presence of herbaceous species (n = 54, α = 0.05; average ± standard deviation). * indicates significance; n.s indicates no significance.
Herbaceous Speciesn° S-Tn° Cp ValueResult
Asperula odorata L.14.9 ± 13.06.9 ± 9.50.08n.s
Carex pendula L.7.8 ± 6.33.6 ± 4.50.09n.s
Euphorbia amygdaloides L.9.6 ± 20.320.3 ± 13.10.94n.s
Mercurialis perennis L.2.7 ± 4.88.0 ± 17.80.12n.s
Potentilla reptans L.3.7 ± 5.42.1 ± 4.20.56n.s
Sanicula europaea L.0.1 ± 0.30.4 ± 1.00.07n.s
Solanum kieseritzkii C.A. Mey.1.7 ± 4.01.7 ± 2.30.59n.s
Viola alba Bess.7.1 ± 8.70.0 ± 0.00.99n.s
Brachypodium sylvaticum (Huds).0.0 ± 0.01.9 ± 5.70.04*
Circaea lutetiana L.0.4 ± 0.90.0 ± 0.00*
Drypotris affines L.1.3 ± 1.03.0 ± 3.50.05*
Epimedium pinnatum L.0.0 ± 0.00.2 ± 0.70.04*
Epipactis helleborine (L) Crantz.0.2 ± 0.70.0 ± 0.00.04*
Geranium sp.0.1 ± 0.30.0 ± 0.00.04*
Hypericum androsaemum L.0.8 ± 1.73.8 ± 5.50*
Lamium album L.0.7 ± 1.41.9 ± 3.00*
Lapsana communis L.0.2 ± 0.40.0 ± 0.00*
Luzula pilosa (Smith) DC.0.0 ± 0.00.2 ± 0.70.04*
Menta aquatica L.0.1 ± 0.30.0 ± 0.00.04*
Mentha sp.1.7 ± 2.81.0 ± 2.10.02*
Oplismenus undulatifolius (Ard).0.0 ± 0.02.2 ± 6.70.02*
Poa sp.0.8 ± 2.30.0 ± 0.00.04*
Rubus hyrcanus Juz.0.6 ± 1.13.1 ± 4.10*
Scutellaria tournefortii Beneth.0.1 ± 0.30.0 ± 0.00*
Viola odorata L.7.1 ± 8.70.0 ± 0.00*
Table 5. Results of independent t-test on the effect of time since harvest and traffic intensity in skid trails on herbaceous species. * indicates significance (n = 54, α = 0.05).
Table 5. Results of independent t-test on the effect of time since harvest and traffic intensity in skid trails on herbaceous species. * indicates significance (n = 54, α = 0.05).
Time15 Years Since Harvest
(Compartment no. 213)		10 Years Since Harvest
(Compartment no. 319)		5 Years Since Harvest
(Compartment no. 315)
Traffic/SpeciesLowMediumHighLowMediumHighLowMediumHigh
Asperula odorata0.02 *0.03 *0.02 *0.880.080.02 *0.530.05 *1
Carex pendula-0.02 *0.090.130.070.02 *0.120.150.07
Euphorbia amygdaloides0.230.05*0.02 *0.290.090.02 *0.040.180.05 *
Mercurialis perennis--0.02 *0.05 *0.890.02 *--0.02 *
Viola alba0.02 *0.290.120.02 *0.070.05 *0.040.560.02 *
Table 6. Effect of logging operations on the number of herbaceous plants. * indicates statistical significance (n = 54, α = 0.05; average ± standard deviation). Skid trail (S-T) and control (C).
Table 6. Effect of logging operations on the number of herbaceous plants. * indicates statistical significance (n = 54, α = 0.05; average ± standard deviation). Skid trail (S-T) and control (C).
Comparison of Statistical Results for the Traffic Intensity Factor for all Herbaceous Plants with Those for the Control
1Low traffic intensity (average n° S-T 30.6 ± 21.5; average n° C 30.9 ± 19.3) 0.62
2Medium traffic intensity (average n° S-T 17.6 ± 9.7; average n° C 24.7 ± 14.2)0.40
3High traffic intensity (average n° S-T 19.3 ± 9.7; average n° C 33.1 ± 18.9)0.02 *
Comparison of statistical results between traffic intensity levels
1Low traffic intensity (average n° S-T 30.6 ± 21.5) vs. medium traffic intensity (average n° S-T 17.6 ± 9.7)0.93
2Low traffic intensity (average n° S-T 30.6 ± 21.5) vs. high traffic intensity (average n° S-T 19.3 ± 9.7)0.00 *
3Medium traffic intensity (average n° S-T 17.6 ± 9.7) vs. high traffic intensity (average n° S-T 19.3 ± 9.7)0.00 *
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Babaei-Ahmadabad, A.; Jourgholami, M.; Lo Monaco, A.; Venanzi, R.; Picchio, R. Mid-Term Evaluation of Herbaceous Cover Restoration on Skid Trails Following Ground-Based Logging in Pure Oriental Beech (Fagus orientalis Lipsky) Stands of the Hyrcanian Forests, Northern Iran. Land 2025, 14, 1387. https://doi.org/10.3390/land14071387

AMA Style

Babaei-Ahmadabad A, Jourgholami M, Lo Monaco A, Venanzi R, Picchio R. Mid-Term Evaluation of Herbaceous Cover Restoration on Skid Trails Following Ground-Based Logging in Pure Oriental Beech (Fagus orientalis Lipsky) Stands of the Hyrcanian Forests, Northern Iran. Land. 2025; 14(7):1387. https://doi.org/10.3390/land14071387

Chicago/Turabian Style

Babaei-Ahmadabad, Ali, Meghdad Jourgholami, Angela Lo Monaco, Rachele Venanzi, and Rodolfo Picchio. 2025. "Mid-Term Evaluation of Herbaceous Cover Restoration on Skid Trails Following Ground-Based Logging in Pure Oriental Beech (Fagus orientalis Lipsky) Stands of the Hyrcanian Forests, Northern Iran" Land 14, no. 7: 1387. https://doi.org/10.3390/land14071387

APA Style

Babaei-Ahmadabad, A., Jourgholami, M., Lo Monaco, A., Venanzi, R., & Picchio, R. (2025). Mid-Term Evaluation of Herbaceous Cover Restoration on Skid Trails Following Ground-Based Logging in Pure Oriental Beech (Fagus orientalis Lipsky) Stands of the Hyrcanian Forests, Northern Iran. Land, 14(7), 1387. https://doi.org/10.3390/land14071387

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