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Article

Impact on Soil Physical Properties Related to a High Mechanization Level in the Row Thinning of a Korean Pine Stand

by
Kigwang Baek
1,
Eunjai Lee
1,*,
Hyungtae Choi
2,
Minjae Cho
1,
Yunsung Choi
1 and
Sangkyun Han
3
1
Forest Technology and Management Research Center, National Institute of Forest Science, Pocheon 11187, Korea
2
Forest Environment and Conservation Department, National Institute of Forest Science, Seoul 02455, Korea
3
Division of Forest Sciences, College of Forest and Environmental Sciences, Kangwon National University, Chuncheon 24341, Korea
*
Author to whom correspondence should be addressed.
Land 2022, 11(3), 329; https://doi.org/10.3390/land11030329
Submission received: 22 January 2022 / Revised: 22 February 2022 / Accepted: 22 February 2022 / Published: 24 February 2022
(This article belongs to the Special Issue Influence on Soil Quality of Agriculture and Forest Management: Assessment, Mitigation and Best Management Practices)
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Abstract

:
In ground-based harvesting, machine traffic can cause soil physical disturbances including excessive compaction, the displacement of the soil surface and topsoil, and rutting. These impacts can indirectly hamper seedling survival and tree growth because of reduced soil permeability and root growth. However, the extent of soil disturbance in mechanized row thinning by harvester and forwarder systems in South Korea is unclear. Therefore, our objectives were to determine the impacts of two types of harvesters, soil textures, and extraction methods on soil compaction and rutting in a Korean Pine stand. The results showed that the machine passes affected soil disturbances. The soil bulk density inside the tracks (at 0–10 and 10–20 cm soil depths) after harvester passes (wheeled vs. tracked) increased by 17 and 27% and 30 and 20%, respectively. The largest impact was recorded for the forwarding track and significant differences were observed between the track and reference locations. Furthermore, the rutting depth in the forwarding trails was significantly higher than in the harvester trails. Thus, the application of a brush mat on harvester and forwarder trails may reduce machine-induced soil compaction. These results provide useful information to help forest engineers and field managers design environmentally sound ground-based harvesting operations.

1. Introduction

Korean Pine (Pinus koraiensis Sieb. et Zucc.) forests, extended in the northern region of South Korea (hereafter Korea), cover approximately 70% of the total Korean Pine forest area (170 thousand hectares (ha); [1]). This species produces high-value wood products and nuts; 38% of the total Korean Pine forest area is in a 40 year age class stand, causing an increase in thinning operations [1,2,3]. Particularly in Russia, Korean Pine forests perform an essential role for tiger conservation [4]. However, a dramatic decrease of the Korean Pine forests can be attributed to insect pests and forest fires in Korea and Japan [5]. In Northeast China and Russia, Korean Pine forests have dangerously decreased due to extensive and excessive timber harvesting [4,6]. As a result, the management of Korean Pine forests is an urgent issue.
Thinning helps improve the resistance of a stand to enhance the quality of the remaining trees and reduce the risk of stand damage [7,8]. It is a labor-intensive technique that combines motor–manual felling and extraction with manpower or winches. In Korea, this technique is commonly used in selection thinning because of its cost efficiency and ease of use [9]. In addition, new ground-based harvesting systems such as harvester felling, forwarding, and row thinning (recently introduced and commonly called geometric thinning) are being applied to improve productivity and safety. The cost of marking trees to be felled is eliminated by using a mechanized system for row thinning and the open rows serve as convenient trails for extraction [10]. Fujimori [11] reported that although row thinning provides benefits for extracting fallen trees, it has negative consequences for the soil ecosystem. In Korea, however, we found no evidence that heavy machinery operations caused an increased soil disturbance and environmental impact.
Several studies have reported that the operations of mechanized ground-based harvesting have negative impacts on soil disturbance including soil compaction, displacement, and rutting or puddling [12,13,14]. Soil disturbance induced by forest harvesting depends on several factors such as timber harvesting techniques and equipment [15,16,17], machine passes [18], initial bulk density [19], soil moisture [20], and soil texture [21]. Soil compaction occurs when mechanical pressure is applied to a soil, increasing the bulk density and decreasing the porosity and infiltration [14,22]. Displacement is defined as the shift of topsoil from one location to another laterally by machine traffic, which increases the soil erosion potential [12,14]. Rutting and puddling are induced by both soil compaction and displacement [23]. Thus, excessive traffic from forest machines (e.g., harvesters, forwarders, and skidders) may induce soil disturbance in the forest stand.
During normal harvester operations, brush mats from logging residues (e.g., tree tops, branches, and unmerchantable timber) are purposely left on operating trails to prevent trafficability and mitigate soil disturbances [14,18,24]. The role of brush mats is to reduce soil displacement and ruts [14,25]. For example, several studies have recommended the use of brush mats weighing between 20.0 and 32.1 kg/m2 for soil protection. However, in brush mates weighing between 0 and 10 kg/m2, soil compaction due to machinery is difficult to prevent [24,26,27]. Therefore, logging residues may potentially decrease off-road forest machinery traffic and its impacts.
Soil compaction and displacement can be easily measured through the soil core sampling method and a visual assessment but it is laborious, time-consuming, and costly [12,28]. In addition, proper and efficient sampling has challenged and hindered both foresters and soil scientists because of the high spatial variability in the physical, hydrological, and chemical properties of forest soil [28,29]. In order to evaluate the soil physical properties at a 90–95% confidence level, researchers suggest sample sizes ranging from 3–62 in a 1 ha forest site [19,28]. As a result, a spatial variability in the soil properties may be contemplated before measuring soil disturbance.
Korea is likely to see an increase in the use of mechanized row thinning to improve young-growth forests. Therefore, to maintain soil resilience and forest productivity, it is crucial to understand the effect of the harvester-forwarder system on the soil ecosystem. The main objective of the present study was to determine the impacts of row or strip thinning on soil disturbance in two harvester-forwarder systems. The study aimed to: (1) determine the extent of soil compaction after a mechanized row thinning operation; and (2) evaluate the rut depth along the machine operating trails after traffic on a no-brush mat cover of soil.

2. Materials and Methods

2.1. Description of the Study Area

The row thinning operations were performed in the experimental forests of the National Institute of Forest Science, Namyangju-si, Gyeonggi-do, Korea, in September 2021 (Figure 1). From September to October 2021, unit A (127°10′42.36″ E, 37°44′18.84″ N: WGS84 coordinate system) and unit B (127°10′39.96″ E, 37°44′19.90″ N: WGS84 coordinate system) were harvested at the same time. The total precipitation was 197.1 mm and the rainfall intensity was 0.3 mm/h from 1 September to 31 October [30]. Both stands were 60 years old and even-aged plantations of Pinus koraiensis Sieb. et Zucc. The thinning was applied with 2 rows of cutting and 3 rows of retaining. Table 1 represents the detailed information of the stand characteristics. The 2.6 ha study site had a steep topography ranging from 29.4% ± 14.3 (unit A) to 32.0% ± 14.9 (unit B) in slope degrees. The average values of tree diameters at breast height as well as height in the area were 29.9 cm and 19.0 m, respectively, with an average stand volume of 506.4 m3/ha. The soil type was Cambisol, according to the World Reference Base for Soil Resources. The soil at unit A was classified as clay loam (42% sand, 26% silt, and 32% clay) whereas the soil at unit B was classified as sandy clay loam (53% sand, 23% silt, and 24% clay).
On each unit, an integrated harvesting system was used with the cut being performed by a wheel. The logs and residues were separately transported by the forwarder from the felling site to a main landing. The Korean Pine forests were harvested using a Konrad Highlander 6 × 6-wheel harvester (weight 26,200 kg; Konrad Forsttechnik Gmbh, Preitenegg, Austria) and a Neuson 132HVT tracked harvester (mass 14,400 kg; Neuson Forest Gmbh, Linz, Austria) to fell the trees and extract whole trees for the forwarding trails. The 6-wheel machine dimensions were 2.9 m (W) × 3.8 m (H) × 11.9 m (L) and the tracked machine was 2.6 m (W) × 3.4 m (H) × 7.5 m (L). Whole trees were finally processed and sorted to utilize the logging residues. Each machine had a different equipment operator with the operator of the tracked harvester having more than three years of experience and the highlander having one year of experience. During the felling operations, the logging slash was intentionally left uncovered on the operating trails to use renewable energy and resources. The forwarding operation was performed by the same machine (Forwarder LVS720; Novotný r.o., Hrabová, Czech Republic) with the same driver at both units. The machine dimensions were 2.2 m (W) × 3.3 m (H) × 8.3 m (L). The 8 × 8 forwarder separately carried the logs and residues by more than 10 passes to a landing and was not trafficked on the harvester operating trails. The forwarder used in this study for the extraction cycles weighed 8500 kg when empty and 16,500 kg when loaded.

2.2. Data Collection

After the completion of the thinning, the soil samples were collected using the core sampling method from three trial locations: in one of the tracks, at the centerline, and 2 m outside the track (Figure 2). A 98 cm3 (5 cm inner diameter, 5 cm length) soil corer (Eijkelkamp Soil & Water, Giesbeek, Netherlands) was used to collect the soil samples from two depths: 0–10 and 10–20 cm. The samples were collected on the harvester tracks and forwarder trails at 2 m intervals. Ampoorter et al. [31] and Allman et al. [32] reported that the increase in the soil bulk density caused by forest machinery was confined to a depth of 0–20 cm of soil. A total of 3 transects with 90 samples were collected in the tracked harvester and 4 transects with 96 samples were collected in the wheeled harvester. One line per forwarder trail was selected with 60 samples in order to evaluate soil compaction. We also measured the duff thickness (cm) and volume (g/cm3) at 30 measurement locations. The soil moisture, soil bulk density, and porosity were calculated after oven-drying at 105 °C to a constant weight. A similar method of soil compaction for analysis was used by Naghdi et al. [21] and Hwang et al. [24].
In addition to the soil parameters, soil displacement was measured by a ruler using a cross-sectional measurement method. The bulge and indented areas of the rut were observed every 10 cm after the harvester or forwarder passes. A comparable method of soil displacement was reported by Poltorak et al. [14] and Cambi et al. [33]. All measurements were completed one week post-thinning.

2.3. Statistical Analyses

Statistical analyses were performed using the R statistical package (version 4.1.2). All data were confirmed for normality (Shapiro–Wilk test) and homogeneity of variance (Levene’s test). Analysis of variance (ANOVA) and post-hoc tests (Turkey HSD and Games–Howell tests) were applied to evaluate the statistical differences between the areas. In addition, the non-parametric Kruskal–Wallis test was used to evaluate the rut depth data because of its heteroscedasticity.

3. Results

3.1. Effects of Harvester Traffic on Soil Compaction

The pre-thinning mean litter and duff layer at unit A was 3.7 ± 0.33 cm thick and 9.6 ± 0.97 kg/m3 in volume; at unit B, it was 4.8 ± 0.28 cm thick and 7.6 ± 0.88 kg/m3 in volume. There were no significant differences between the two units (p-value > 0.05). In addition, the average soil moisture was 34% in unit A and 27% in unit B throughout the whole field work period.
The bulk density and porosity showed significant differences between the tracks and reference and the tracks and center at 0–10 and 10–20 cm depths. However, no significant differences were observed between the bulk density and porosity at the reference and the center at the same depth (Table 2). In unit A, the post-felling mean bulk density in the track locations at 0–10 and 10–20 cm soil depths were 1.23 and 1.41 g/cm3, respectively. In unit B, the bulk density in the tracked locations at 0–10 and 10–20 cm soil depths were 1.39 g/cm3 and 1.42 g/cm3, respectively. The porosity in the felling track in both units was statistically lower compared with that in the reference and center. In both units, the track location had significantly different changes in the bulk density and porosity than both the reference and center locations due to the tire contact pressure on the soil surface.
At the track location in unit A, the levels of soil compaction increased with an increasing soil depth but a different pattern was observed in unit B (Figure 3). The mean initial bulk density at the 10–20 cm soil depth in unit A and unit B was 1.11 and 1.20 g/cm3, respectively, with no significant differences (p-value = 0.1826). In addition, there was a significant negative correlation between the initial bulk density and the increase (percent) in the bulk density (Figure 4; p-value = −0.7133 in unit A and -0.8365 in unit B). In unit A, the change in the bulk density increased by 17%; the porosity decreased by 11% at a 0–10 cm depth. In unit B, the change in the bulk density increased by 30%; the porosity decreased by 21% at a 0–10 cm depth. The increase in the bulk density in unit B was significantly higher than in unit A (p-value = 0.0075) although the mean initial bulk density was statistically the same. However, in unit A, the alteration rates of the bulk density (increased by 27%) and porosity (decreased by 20%) were statistically higher compared with those in unit B at a 10–20 cm soil depth.
We also observed differences in the rutting between the wheeled and tracked harvesters. During the harvester traffic cycles, a return pass created 10.5 ± 0.54 and 9.0 ± 0.56 cm rut depths in unit A and B, respectively (Table 3). The rut depths in the wheeled harvester track were significantly higher than those of the tracked harvester tracks (p-value = 0.1726). This section, divided by subheadings, should provide a concise and precise description of the experimental results and their interpretation as well as the experimental conclusions that could be drawn.

3.2. Effects of Forwarder Traffic on Soil Compaction

Significant differences were observed in the post-forwarding mean bulk density for the reference, track, and center locations at 0–10 cm and 10–20 cm depths (p-value < 0.001). After forwarding, the mean bulk densities for the reference, track, and center locations at a 0–10 cm depth were 1.06, 1.50, and 1.24 g/m3, respectively (Table 4). The porosity in the forwarding track was significantly lower than in the reference and center locations at depths of 0–10 and 10–20 cm (p-value < 0.001). In addition, the bulk density and porosity were statistically different between the reference and center at the 0–10 cm and 10–20 cm soil depths (p-value < 0.001).
To assess the observed soil compaction-induced changes, the changes in the bulk density in the track locations at 0–10 cm (increased by 41%) and 10–20 cm (increased by 33%) were compared with those at the reference (Figure 5 andFigure 6). At the center location, the bulk density increased by 17% and 11% at soil depths of 0–10 and 10–20 cm, respectively. The porosity at a 0–10 cm soil depth decreased by 28% in the track and by 11% in the center. In addition, the porosity in the track was significantly lower than in the reference and center locations. As a result, the highest changes were recorded in the track locations compared with the reference and center.
In our study, the post-forwarding rut depth ranged from 4–38 cm with no logging residues. The average rut depth was 14.5 cm with a small variation range of 0.454 for 16 transects. Furthermore, the rut depth in the forwarding trails was significantly deeper with the number of machine passes than in the harvester trails (p-value < 0.001).

4. Discussion

Mechanized harvesting operations can adversely impact on the soil environment causing soil compaction, displacement, and rutting. In Korea, such technologies, particularly harvester-forwarder systems and row thinning, are being applied to improve productivity and safety. However, research on soil disturbances associated with thinning operations by harvesters and forwarders in a Korean Pine (Pinus koraiensis Sieb. Et Zucc.) stand is missing. Therefore, the objective of the present study was to determine soil disturbances caused by row thinning using a harvester and forwarder system. Field tests such as soil core sampling and cross-sectional measurements were performed to evaluate soil compaction in three different locations: the reference, track, and center. The results showed that the largest changes in the bulk density and porosity were observed in the track locations of the harvester and forwarder trails. In particular, during forwarding operations, both the track and center had significantly higher soil compaction risks than the reference location. In addition, a deeper rut depth was noted in the forwarding trails than in the harvester trails. This information may be used to identify potential alterations in soil disturbance and provide a decision support to minimize the adverse impacts on the soil environment and improve future stand production.
Mechanized harvesting has the potential to change the physical properties of soil (e.g., the bulk density and porosity) and to create ruts. After forest operations, it was noted that the extent of compaction increased by 70% [33,34]. The change rates in the bulk density in unit A and unit B were greater than 15% and these rates had a detrimental effect on soil compaction [35]. The soil surface is affected by soil compaction and rutting, depending on logging conditions such as the machine type (wheeled harvester or tracked harvester). For example, Allman et al. [15], Cambi et al. [33], and Sheridan [36] found that a tracked harvester compacted the soil less than a wheeled harvester. In contrast, our results showed that the tracked harvesters showed a higher increase in the bulk density and porosity at a 0–10 cm soil depth. These results were similar to several previous studies, which reported that although a tracked harvester is lighter than a wheeled harvester, it causes significantly higher soil compaction [37,38]. This can be explained by the aggressive locomotion and more vibrational drive systems [33,38]. Thus, tracked harvester activity may cause excessive soil compaction compared with a wheeled harvester. Further, these operations could induce adverse effects on the hydrological dynamic as well as soil erosion and sediment runoff by rainfall [39].
Soil compaction may be greatly influenced by the soil texture and particle size. Researchers have reported that fine- to medium-textured soil was more vulnerable to compaction and rut depth by machine traffic than coarse-textured soil [40,41]. However, if fine-textured soil (e.g., clay loam) had a considerable amount of shrink-swell clay, the degree of soil compaction was lower than sand [21,42]. The results of this study showed that the bulk density and porosity at a 0–10 cm soil depth in the tracked harvester tracks on sandy clay loam showed a significantly higher degree of soil compaction than on clay loam. An increased pore size and continuity adversely affect soil compaction in the upper layer of coarse-textured soil [31]. Ampoorter et al. [31] also reported that due to a low cohesion in high-sand soils, both soil compaction and rutting occurred after traffic. However, we observed that the rut depth due to the wheeled harvester track on the clay loam was considerably deeper than that due to the tracked harvester. This result was consistent with a previous study by Naghdi et al. [21] who observed the effect of the soil texture (clay loam vs. sandy loam) on the extent of rutting and reported that a minimal cohesion between the soil particles in high-clay soils under moist conditions led to rut formations. As a result, the ratio of soil compaction, rutting, and plastic deformation depended on the soil texture.
Forwarders are more frequently driven with heavier loads than harvesters, thus explaining the higher extent and degree of soil damage in forwarder trails. Damage increase commonly depends on the number of passes [43]. Although most of the potential compaction impact occurs after the first pass, it has been demonstrated that the maximum compaction of soil followed within 10 equipment passes [12]. Our findings could be described by the behavior of the forwarding activities. The number of forwarder passes was greater than harvester passes and the soil in the track and center locations became more sensitive to compaction with an increasing rut depth than in the reference. During forwarding operations, the logs are moved to the landings and soil disturbance is caused by exerted tire pressure and wheel slippage [43,44,45,46,47]. The level of compaction increases with the increase in the machine mass and the contact area between the tire and soil surface [48]. Therefore, during forwarding, the logs are loaded and transported on a forwarding trailer along the forwarding trail, thus affecting soil compaction and displacement.
During ground-based mechanized harvesting, this technology has led to compact soil associated with adverse hydrological conditions, which consecutively increase soil erosion and sediment loss [13,33,49]. In addition, soil displacement can negatively affect soil erosion and sediment transport because of the removal of the ground cover and topsoil by equipment traffic [12]. If not adequately operated, mechanized harvesting could lead to soil compaction and erosion, particularly along the trails [13]. Although soil erosion is impossible to eliminate, it has to be minimized to reduce the impact on human health and aquatic ecosystems in a forested watershed [39,50]. Operational planning tools for mechanized harvesting are used to predict trafficability and minimize soil disturbance [49]. Brush mats on operating trails can avoid severe soil disturbances as they provide beneficial load-distributing capabilities [26,49]. An alternative technology to reduce soil disturbance is to modify the machinery such as wider tires, additional wheels and axles, and flexible steel tracks [49]. To control and minimize the adverse effects of mechanized harvesting, mechanized harvesting operations may be properly designed and completed.

5. Conclusions

In conclusion, this study was the first attempt to understand the effects of harvester and forwarder harvesting systems on soil during a row thinning activity. Soil disturbances including soil compaction and rut formation are concentrated along the machine trails because they are related to the contact of tires on the ground. After the harvester passed, we found a significant difference between the track and reference locations in terms of the bulk density and porosity. In addition, different rates of soil compaction between the wheeled harvester and tracked harvester were observed, with higher impacts from the tracked harvester trails. In the forwarding trails, significant differences in the impacts between the track and center were observed; the center and reference locations had the highest impact in the track. Furthermore, we found a significant difference associated with the rut depth between the forwarder trail and the harvester trail. These results may be well-supported to ameliorate soil disturbances for mechanized harvesting operations. Future research is needed to monitor soil compaction, rutting, and displacement in field studies and to develop a soil trafficability model under different conditions including the slope, soil texture (i.e., loam, sandy loam, and clay), moisture content, and brush mats of different amounts.

Author Contributions

Conceptualization, E.L., K.B. and H.C.; methodology, K.B., M.C., Y.C. and S.H.; formal analysis, K.B., E.L., M.C. and Y.C.; investigation, K.B., E.L., M.C., Y.C. and S.H.; resources, K.B., E.L., M.C. and Y.C.; data curation, K.B., M.C., Y.C. and S.H.; writing—original draft preparation, K.B. and E.L.; writing—review and editing, E.L., H.C. and S.H.; visualization, K.B. and E.L.; supervision, E.L. and H.C.; project administration, E.L. and H.C.; funding acquisition, E.L. and H.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Land 11 00329 g001 550
Figure 1. Map of the study site and images of the harvesters ((a): Konrad Highlander wheeled harvester; (b): Neuson 132HVT tracked harvester) and forwarder ((c): Novotný LVS720) used in row thinning operations.
Figure 1. Map of the study site and images of the harvesters ((a): Konrad Highlander wheeled harvester; (b): Neuson 132HVT tracked harvester) and forwarder ((c): Novotný LVS720) used in row thinning operations.
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Figure 2. Sample points (control, track, and center) along the harvester and forwarder trails.
Figure 2. Sample points (control, track, and center) along the harvester and forwarder trails.
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Figure 3. Percentage increase in bulk density and decrease in porosity on the track after harvester passing at 0–10 cm and 10–20 cm soil depths at unit A and unit B.
Figure 3. Percentage increase in bulk density and decrease in porosity on the track after harvester passing at 0–10 cm and 10–20 cm soil depths at unit A and unit B.
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Figure 4. The correlation between initial soil bulk density and percent increase in bulk density.
Figure 4. The correlation between initial soil bulk density and percent increase in bulk density.
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Figure 5. Percentage increase in bulk density and decrease in porosity on the track and center locations after forwarder passing at 0–10 cm and 10–20 cm soil depths.
Figure 5. Percentage increase in bulk density and decrease in porosity on the track and center locations after forwarder passing at 0–10 cm and 10–20 cm soil depths.
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Figure 6. The correlation between initial soil bulk density and percent increase in bulk density in forwarding trail.
Figure 6. The correlation between initial soil bulk density and percent increase in bulk density in forwarding trail.
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Table
Table 1. Stand characteristics of the study site.
Table 1. Stand characteristics of the study site.
Thinning Unit
Unit AUnit BCombined
Area (ha)1.41.22.6
Mean DBH a (cm)31.828.530.2
Mean height (m)18.819.119.0
Basal area (m2/ha)51.861.456.5
Trees per hectare 624902760
Stand volume (m3/ha)445.1569.9506.4
Soil textureClay loamSandy clay loam-
a Diameter at breast height.
Table
Table 2. Mean bulk density and porosity calculated at reference, track, and center locations in the harvester trails.
Table 2. Mean bulk density and porosity calculated at reference, track, and center locations in the harvester trails.
UnitSoil Depth (cm)nReferenceTrackCenterp-Value
Bulk density (g/cm3)
A0–10161.05 ± 0.04 a1.23 ± 0.03 b1.02 ± 0.04 a0.0002
10–20161.11 ± 0.05 a1.41 ± 0.03 b1.11 ± 0.05 a<0.001
B0–10151.07 ± 0.05 a1.39 ± 0.04 b1.18 ± 0.03 a0.0002
10–20151.20 ± 0.03 a1.42 ± 0.02 b1.22 ± 0.03 a<0.001
Porosity (%)
A0–101659 ± 0.02 a53 ± 0.01 b61 ± 0.01 a<0.001
10–201657 ± 0.02 a43 ± 0.01 b57 ± 0.02 a<0.001
B0–101559 ± 0.02 a47 ± 0.01 b55 ± 0.01 a<0.001
10–201554 ± 0.01 a46 ± 0.01 b53 ± 0.01 a<0.001
a, b Values with same letter are not statistically different (p > 0.05).
Table
Table 3. Mean rut depth between wheeled and tracked harvester tracks.
Table 3. Mean rut depth between wheeled and tracked harvester tracks.
UnitnRut Depth (cm)
A1610.5 ± 0.54
B159.0 ± 0.56
Table
Table 4. Mean bulk density and porosity calculated at reference, track, and center locations in the forwarding trails.
Table 4. Mean bulk density and porosity calculated at reference, track, and center locations in the forwarding trails.
Soil Depth (cm)nReferenceTrackCenterp-Value
Bulk density (g/cm3)
Trails0–10151.06 ± 0.03 a1.50 ± 0.04 b1.24 ± 0.04 c<0.001
10–20151.15 ± 0.03 a1.54 ± 0.02 b1.28 ± 0.10 c<0.001
Porosity (%)
Trails0–101559 ± 0.01 a42 ± 0.01 b52 ± 0.02 c<0.001
10–201556 ± 0.01 a41 ± 0.01 b51 ± 0.04 c<0.001
a, b, c Values with same letter are not statistically different (p > 0.05).
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MDPI and ACS Style

Baek, K.; Lee, E.; Choi, H.; Cho, M.; Choi, Y.; Han, S. Impact on Soil Physical Properties Related to a High Mechanization Level in the Row Thinning of a Korean Pine Stand. Land 2022, 11, 329. https://doi.org/10.3390/land11030329

AMA Style

Baek K, Lee E, Choi H, Cho M, Choi Y, Han S. Impact on Soil Physical Properties Related to a High Mechanization Level in the Row Thinning of a Korean Pine Stand. Land. 2022; 11(3):329. https://doi.org/10.3390/land11030329

Chicago/Turabian Style

Baek, Kigwang, Eunjai Lee, Hyungtae Choi, Minjae Cho, Yunsung Choi, and Sangkyun Han. 2022. "Impact on Soil Physical Properties Related to a High Mechanization Level in the Row Thinning of a Korean Pine Stand" Land 11, no. 3: 329. https://doi.org/10.3390/land11030329

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