Timber Harvesting Operations Research Articles

A case study of the subjective workload of forest equipment operators in South Carolina

ABSTRACT Logging operations in the Southern United States have become more mechanized over time. However, extensive use of complex and heavy forest machineries for long durations increases operator workload, especially the cognitive demand. Working under demanding conditions can decrease the health of forest equipment operators over time, reducing productivity and increasing the risk of accidents. This study provides an initial assessment of the workload of logging equipment operators during timber harvesting operations using conventional wheeled feller-buncher, grapple skidder, and knuckle-boom loader harvesting systems by assessing the subjective workload of the logging equipment operators in South Carolina. In addition, we observed the heart rate of equipment operators to study the activities causing excessive physical and mental workload. Logging equipment operators self-evaluated their workload using the NASA Task Load Index, a subjective measure of workload. Results show no significant difference in the overall workload of equipment operators working at clearcut and thinning sites. The workload dimensions of Effort and Frustration contributed the most to the overall workload, while Performance had the least contribution. Sudden heart rate spikes occurred when operators conducted physical activities such as clearing debris from a felling head but were otherwise unobserved.

Assessing the Extent and Severity of the Impact on Forest Soils of Two Different Fully Mechanized Timber Harvesting Operations

Recently, the use of powerful and heavy vehicles for timber harvesting on flat or slightly sloping terrains has been widely expanded to provide safe working conditions and high productivity. However, soil disturbances during ground-based mechanized operations in South Korea are not fully investigated and difficult to avoid. Therefore, we compared the soil displacement and compaction (bulk density and hydraulic conductivity) between two different operations: cut-to-length (CTL) logging with a harvester and forwarder, and whole-tree (WTH) logging with a harvester and skidder. After clear-cutting, severe visual disturbances and rut depths were more prevalent in the forwarding trails than in the skidding trails. The CTL harvesting method created larger amounts of slash (6.9 kg/m2) along the trails than the WTH harvesting did (1.8 kg/m2). We found a significant difference in the compaction between the reference and the track and a negative correlation between the slash quantity values and the percentage increase in compaction. Our results showed that using skidding extraction can cause more severe impacts than forwarding extraction. Thus, these results may be helpful in understanding the influence of ground-based CTL and WTH harvesting operations and achieving best practices to minimize the environmental impacts on soil.

Evaluation of Productivity and Cost Analysis on a Combined Logging System

The efficient planning and control of timber harvesting operations is crucial to growth productivity and reducing costs, and different systems or methods are applied to obtain elevated performance. In particular, cable yarding is a highly appreciated and very efficient wood extraction method in areas that are difficult to access with ground-based extraction machines. Combined logging systems are not diffuse and not often implemented. For this reason, the use and the application of innovative methods are limited. However, some combinations have recently been observed in forest operations. This study, conducted in a deciduous stand in Bulgaria, paid attention to the combination of a tractor-mounted tower yarder (Valentini V400) with a clambunk skidder (Timberjack 1010D), aiming to examine the viability and develop the operational efficiency of the two-stage extraction system and to define the time, log volume extracted per unit by the yarder and the clambunk, and the yarding and skidding costs. The researchers carried out a time-motion study and performed a regression analysis to identify those variables that are most likely to affect the duration of work elements and productivity. For cost analysis, the COST model was used. The mean productivity of the tower yarder was 10.34 m3/PMH and 8.11 m3/SMH, while for the clambunk skidder, the productivity was 6.23 m3/PMH and 4.93 m3/SMH. The net costs for the combined logging system were calculated as 120.87 €/PMH and 14.93 €/m3. This study adds new data about the correct use of both machines, supporting their application in beech forests.

Maximizing the economic benefit for cable yarding timber harvesting operations by spatially optimizing tree selection

Maximizing the economic benefit for cable yarding timber harvesting operations by spatially optimizing tree selection

Camping in clearcuts: The impacts of timber harvesting on USFS campground utilization

This research applies a temporally and spatially explicit model to analyze timber harvesting's impact on campground utilization on United States Forest Service (USFS) land across the Western U.S. Timber harvesting and camping can occur near one another due to multiple-use management strategies used by the USFS. However, intensive forest management can change the degree of perceived naturalness of a forest and may therefore negatively impact recreation. We investigate several facets of harvesting activity, such as proximity to camping, type of harvesting, regional differences, and persisting lagged impacts of timber harvesting. We find that harvesting activity significantly decreases campground reservations during the year of harvest, and this loss in campground utilization can be expected to have negative impacts on nearby tourism-dependent economies. Management implications•Intensive forest management generally negatively impacts campground utilization during the years of operations•Public land managers, such as the USFS, may seek to locate timber harvesting operations further from campgrounds if they wish to not negatively impact campground usage•Alternative, less-intensive, forms of forest management decrease nearby campground utilization less than timber harvesting, so do not necessarily need to be located further from campgrounds to avoid losses in their utilization•Decreased campground visitation due to timber harvesting may imply lower visitation to nearby gateway communities, and therefore less economic stimulation and spending in their economies, which may create an incentive for gateway communities to be involved in the harvest planning process

A Prototype for Automated Delimitation of Work Cycles from Machine Sensor Data in Cable Yarding Operations

The demand for increased efficiency in timber harvesting has traditionally been met by continuous technical improvements in machines and an increase in mechanisation. The use of active and passive sensors on machines enables improvements in aspects such as operational efficiency, fuel consumption and worker safety. Timber harvesting machine manufacturers have used these technologies to improve the maintenance and control of their machines, to select and optimise harvesting techniques and fuel consumption. To a more limited extent, it has also been used to evaluate the time taken to complete tasks. The systematic use of machine sensor data, in a central database or cloud solution is a more recent trend.Machine data is recorded over long periods of time and at high resolution. This data therefore has considerable potential for scientific investigations. For mechanised timber harvesting operations, this could include a better understanding of the interaction between productivity and operational parameters, which first of all requires an efficient determination of cycle time.This study was the first to automatically delimitate tower yarder cycle times from machine sensor data. In addition to machine sensor data, cycle times were collected through a traditional manual time and motion study, and cycle times from both studies were compared to a reference cycle time determined from video footage of the yarder in operation.Based on three days of detailed time study, the total cycle time in the classic manual time (–1.3%) and in the machine sensor data (–1.2%) was only slightly shorter than in the reference study, and the average cycle time did not differ significantly (classic manual time study: –0.08±0.94 min, p=0.997; machine sensor data study: –0.08±0.26 min, p=0.997). However, the accuracy of the machine sensor approach (RMSE=0.92) was more than three times higher than that of the classic manual time study (RMSE=0.27).With the integration of sensors on forestry machines now being commonplace, this study shows that machine sensor data can be reliably interpreted for time study purposes such as machine or system optimisation. This eliminates the need for manual time study, which can be both cumbersome and dependent on the experience of the observer, and allows long term data sets to be obtained and analysed with comparatively little effort. However, a truly automated time study needs to be supplemented with automated determination of and linkage to other operational parameters, such as yarding and lateral yarding distance or load volume.

Integrated economic and environmental modeling of forest biomass for renewable energy in California: Part I - Model development

Forests are a major natural resource of the state of California, where over a third of the land is forested, and provide a wide range of environmental, economic, and social benefits. Over the past decade, unprecedented drought, insect outbreaks and wildfires have resulted in large-scale tree mortality that greatly affects the forest ecosystem and poses significant threat to human health and welfare and to the environment. Forest thinning and management is considered imperative to improve forest health and resilience. Forest resources including dead and dying trees as well as the residues produced from forest thinning and timber harvesting operations could potentially be used to a greater degree than at present to generate electricity and other renewable energy to meet the increasing demand for more sustainable supplies and mitigate the risk of wildfires. However, efforts to construct new electricity generation capacity in the state at any scale over the last several decades have faced both economic and environmental challenges. As needs for alternative management approaches have become clear, opportunities have emerged for new bioenergy projects. These projects need to be effectively planned and potential economic and environmental performance carefully evaluated. Toward this purpose, an integrated framework model for lifecycle and technoeconomic assessment was developed to quantify environmental and economic impacts, initially for generating electricity using forest resources and with associated web services developed for an online application (forestdss.ucdavis.edu) that allows potential users to quickly estimate the economic and environmental performance of a potential facility at specified locations.

VISIBILITY AND POSTURE OF OPERATORS IN HARVESTERS WITH LATERAL AND FRONT COUPLING CRANES

In mechanized timber harvesting operations, it is possible to verify ergonomic inadequacies, such as poor visibility and inappropriate postures, which can cause risks to the safety and health of workers, with effects on the operational performance of the machines. In this context, the objective of this work was to evaluate the effects of the positioning of the coupling crane in harvesters concerning the visibility and postures of forestry operators. For this, the study was carried out in clear-cutting operations in eucalyptus stands, evaluating a harvester with a frontal coupling crane and another with lateral coupling, as well as operators per machine. To determine effective times and typical postures, filming and freezing of images were performed. Then, the Skogforsk and Rapid Upper-Limb Assessment (RULA) methods were used to assess visibility and posture, respectively. Angulation and posture data were compared between machines by the Student's t test. Front and side visibility remained within acceptable limits, but the side crane harvester required operators to have an average head tilt angle of 15º, 50% higher than with the front crane. Consequently, in the postural evaluation, the one with the lateral crane presented score 3 and action level 2 86% of the time, suggesting further investigations, while the other presented score 2 and action level 1 81% of the time, being acceptable if not maintained or repeated for long periods. Therefore, the positioning of the crane coupling on the machine requires a reorganization of the workstation, mainly the machine's display.

Classification of Tree Species in the Process of Timber-Harvesting Operations Using Machine-Learning Methods

This article presents the constraining factors that limit the increase in the efficiency of logging production by modern multi-operation machines operating on the Scandinavian cut-to-length technology in the felling phase, namely the selection and registration of wood species. The factors for creating a complete architecture of a fully connected neural network (NN) are given. The dependence of the prediction accuracy of a fully connected NN on a test sample on the size of the training dataset, and an image of the dependence of the prediction accuracy on the number of trees in the random forest method for image classification is shown. For a fully connected NN, a sufficient number of images and a test sample size were established for training, using tree-trunk breed-class labels as target values. A selected list of trees was given, with the size of the training sample of images presenting a problem for the classification of tree trunks using the random forest method. The aim was the discovery of the optimal number of trees necessary to achieve prediction accuracy.

Assessing productivity and cost of timber harvesting during longleaf pine ecosystem restoration

ABSTRACT Timber harvesting operations are increasingly used to restore sensitive habitats such as longleaf pine (Pinus palustris Mill.) ecosystems. However, logging companies are often functionally limited by operational costs and site-specific productivity potential. By employing a time study, this project quantified the cost and productivity of a two-person logging crew using conventional equipment in a South Carolina southern pine timber harvest used to restore a longleaf pine savanna ecosystem. Our study found that the feller-buncher, grapple skidder, and knuckle-boom loader produced, on average, 60.7, 23.6, and 45.2 tonnes per Productive Machine Hour (PMH), respectively. When the knuckle-boom loader was exclusively loading log trucks, productivity increased to 48.4 tonnes per PMH. Additionally, a machine rate analysis found that the total cost for each machine was 108.83 USD, 122.92 USD, and 121.25 USD per PMH, respectively, with a total per tonne cost of cutting, skidding, and loading amounting to 9.68 USD. Our findings indicate that restoration harvesting conducted in this manner under similar environmental conditions and price points may remain profitable for both landowners and logging companies. Moreover, the limitations of operating with a two-person crew resulted in minimal negative effects for both profitability and productivity, making it a viable option for similar restoration operations.

Nth-plant scenario for forest resources and short rotation woody crops: Biorefineries and depots in the contiguous US

• Nationwide depots & biorefineries to meet target costs, quality & quantity from woody resources. • Forest residues: trees, tops & limbs. Short rotation crops: poplar, willow, pine, & eucalyptus. • Maximum accessible forest residues at $79.07/dt & $85.51/dt was 103 and 106 M dt at any ash target. • Short rotation woody crops increased total to 153 & 195 M dt at 1% & 1.75% ash & $85.51/dt cost targets. • Woody resources could address 55% of EPA’s goals, 195 M dt/year at $85.51/dt cost & 1.75% ash target. Estimating the US potential of woody material is of vital importance to ensure cost-effective supply logistics and develop a sustainable bioenergy and bioproducts industry. We analyzed a mature conversion technology for woody resources for the contiguous US that takes advantage of economies of scale: the nth-plant. We developed a database to quantify the total accessible woody biomass within a distributed network of preprocessing depots and biorefineries considering both quality specifications for conversion and a target cost to compete with fossil fuels. We considered two categories of woody biomass: 1) forest residues from trees, tops and limbs produced from conventional thinning and timber harvesting operations as well as non-timber tree removal; and 2) short rotation woody crops such as poplar, willow, pine, and eucalyptus. A mixed integer linear programming model was developed to analyze scenarios with woody feedstock blends at variable biomass ash contents and cost targets at the biorefinery. When considering a target cost of $85.51/dry ton (2016$) at the biorefinery, the maximum accessible biomass from forest residues in 2040 remained constant at 106 million dry tons regardless of ash targets. Including short rotation woody crops as part of the blend increased the total accessible biomass to 153 and 195 million dry tons at ash targets of 1% and 1.75%, respectively. We concluded from our analysis that woody resources could address about 55% of EPA’s (Environmental Protection Agency) target of 16 billion gallons of cellulosic biofuel.

Geostatistical Analysis of Mangrove Ecosystem Health: Mapping and Modelling of Sampling Uncertainty Using Kriging

This study assessed the health of the mangrove ecosystem and mapped the spatial variation in selected variables sampled across the Matang Mangrove Forest Reserve (MMFR) by using a geostatistical technique. A total of 556 samples were collected from 56 sampling points representing mangrove biotic and abiotic variables. All variables were used to generate the semivariogram model. The predicted variables over the entire MMFR have an overall prediction accuracy of 85.16% (AGB), 90.78% (crab abundance), 97.3% (soil C), 99.91% (soil N), 89.23% (number of phytoplankton species), 95.62% (number of diatom species), 99.36% (DO), and 87.33% (turbidity). Via linear weight combination, the prediction map shows that mangrove ecosystem health in Kuala Trong throughout the Sungai Kerang is excellent (5: MQI > 1.5). Some landward areas of Kuala Trong were predicted to have moderate health (3: −0.5 ≤ MQI ≤ 0.5), while Kuala Sepetang was predicted to have the bad ecosystem health (2: −1.5 ≤ MQI ≤ −0.5), with active timber harvesting operations and anthropogenic activities in the landward areas. The results of this method can be utilised to carry out the preferred restoration, through appropriate management and facilities distribution, for improving the ecosystem health of mangroves.

Mapping wheel-ruts from timber harvesting operations using deep learning techniques in drone imagery

AbstractWheel ruts, i.e. soil deformations caused by harvesting machines, are considered a negative environmental impact of forest operations and should be avoided or ameliorated. However, the mapping of wheel ruts that would be required to monitor harvesting operations and to plan amelioration measures is a tedious and time-consuming task. Here, we examined whether a combination of drone imagery and algorithms from the field of artificial intelligence can automate the mapping of wheel ruts. We used a deep-learning image-segmentation method (ResNet50 + UNet architecture) that was trained on drone imagery acquired shortly after harvests in Norway, where more than 160 km of wheel ruts were manually digitized. The cross-validation of the model based on 20 harvested sites resulted in F1 scores of 0.69–0.84 with an average of 0.77, and in total, 79 per cent of wheel ruts were correctly detected. The highest accuracy was obtained for severe wheel ruts (average user’s accuracy (UA) = 76 per cent), and the lowest accuracy was obtained for light wheel ruts (average UA = 67 per cent). Considering the nowadays ubiquitous availability of drones, the approach presented in our study has the potential to greatly increase the ability to effectively map and monitor the environmental impact of final felling operations with respect to wheel ruts. The automated mapping of wheel ruts may serve as an important input to soil impact analyses and thereby support measures to restore soil damages.

Damage to Residual Trees in Thinning of Broadleaf Stand by Mechanised Harvesting System

This research was conducted to determine the cause, intensity and location of damage (stem, butt end, root collar, root) and the extent of damage to standing trees during felling and processing by an harvester and timber extraction by a forwarder (cut-to-length system). The research was conducted in the central part of the Republic of Croatia in the Management Unit (MU) “Bjelovarska Bilogora” during the thinning of Subcompartment 14b, area of 18.28 ha, in the stand of hornbeam (Carpino betuli—Quercetum roboris fagetosum Rauš 1975), age 70, and of Subcompartment 14c, area of 9.07 ha, in a stand of common beech (Carici pilosae—Fagetum Oberdorfer 1957) aged 79 years. The thinning intensity was 12.13% in Subcompartment 14b and 13.72% in Subcompartment 14c. Field measurements were carried out on sample plots—the first time in 2017 to determine the intensity and characteristics of the damage to standing trees with regard to the cause of the damage (harvester or forwarder), and the second time in 2018 to determine the overall intensity and features of the damage to standing trees after finishing harvesting operations. For all trees remaining in the stand after the harvesting operations, the following were determined: tree species, diameter at breast height (DBH), the position of the tree in the stand depending on the forest traffic infrastructure, and—if damaged—cause of damage, type of damage, the position of damage on the tree, and dimensions of damage. The intensity of the damage was expressed by the ratio of damaged and undamaged trees, with a detailed analysis of bark damage (squeezed-bark damage and peeled-bark injuries). The results of the research indicate the highest prevalence of peeled-bark injuries. In relation to the total number of standing trees, trees with peeled-bark injuries were more represented in Subcompartment 14c (39%) than in Subcompartment 14b (33%). In Subcompartment 14b, the harvester and the forwarder damaged an equal number of trees, while in Subcompartment 14c, the harvester damaged 59% of the damaged trees. In both subcompartments, an average of 83% of (peeled bark) injuries were up to 1.3 m above the ground. In both subcompartments, the most common (67%) were injuries up to 100 cm2 in size, for which many authors claim the tree can heal by itself. Given the increasing use of harvester-forwarder systems in deciduous stands and research results that indicate possible damage to standing trees, it is necessary to pay attention to all phases of planning and execution of timber harvesting operations, thus minimising negative effects.

Evaluation of the method of calculating the planned price of timber harvesting operations

Rad se bavi prikazom metode izračuna planskih cijena pridobivanja drva, koje su predmet javnih nadmetanja u Šumsko gospodarskom društvu »Hercegbosanske šume« d.o.o. Kupres te analizom odstupanja planskih od ugovorenih/ostvarenih cijena usluga pridobivanja drva za 97 grupa odjela, koji su bili predmet javnih natječaja u 2019. i 2020. godini. Deskriptivnom i korelacijskom statističkom analizom obuhvaćeni su i pokazatelji grupa odjela na javnim natječajima: površina, neto obujam doznačenog drva, sječna gustoća, broj doznačenih stabala po ha, obujam srednjeg doznačenog stabla, nagib terena, srednja udaljenost privlačenja drva, stjenovitost terena i privlačenje drva uz nagib terena. Test zavisnih parova podataka je ukazao da postoji statistički značajna razlika između planskih i ugovorenih cijena usluga pridobivanja drva (t = 7,78, p < 0,001), a rezultati korelacijske analize potvrdili povezanost utjecajnih čimbenika izvođenja šumskih radova s ugovorenom i planskom cijenom pridobivanja drva. Uslijed statistički značajne (p < 0,05) i vrlo jake korelacije natječajima ostvarene i prikazanom metodom izračunate planske cijene usluge pridobivanja drva, ovisnost je izjednačena linearnim regresijskim modelom uz koeficijent determinacije od 0,667. Navedenim, prikazana je metoda izračuna planske cijene usluge pridobivanja drva dobar prediktor ostvarenih cijena pridobivanja drva na javnim natječajima, što govori i o samoj dobroti prikazane metode izračuna. Slaba i negativna korelacija (p < 0,05, r = -0,22) razlike ugovorene i planske cijene usluge pridobivanja drva o obujmu srednjeg doznačenog stabla, ukazala je da bi ovu pojavu u budućnosti trebalo pratiti s ciljem utvrđivanja uzroka, koji mogu biti: 1) međusobna konkurencija između izvoditelja usluga pridobivanja drva za grupe odjela sa većim srednjim obujmom doznačenoga stabla ili 2) precjenjivanje obujma srednjeg doznačenog stabla u prikazanome modelu izračuna planske cijene pridobivanja drva. Predložene su i smjernice povećanja točnosti određivanja ulaznih parametara (srednja udaljenost privlačenja drva, nagib i stjenovitost terena te privlačenje drva uz nagib terena) prikazane metode izračuna planskih cijena pridobivanja drva u cilju njenog usavršavanja. S obzirom da je izračun vezan za srednju plansku cijenu na razini šumskog gospodarstva, a koju utvrđuje uprava trgovačkog društva, neophodno je stalno praćenje tržišta, kako bi se na vrijeme moglo reagirati ukoliko bi došlo do većih oscilacija.

The Impact of Weather and Slope Conditions on the Productivity, Cost, and GHG Emissions of a Ground-Based Harvesting Operation in Mountain Hardwoods

Mountainous hardwood mixed stands offer challenges to timber harvesting operations in practice, including a harsh climate, variable topography, steep terrain, and large-sized timbers. This paper aims to develop productivity and cost models for a mountain-ground-based harvesting operation across the terrain (e.g., slope conditions), stand (e.g., tree volume) environmental (e.g., weather), and yard (e.g., winching distance) variables and to assess GHG emissions related to the equipment in use. This development was implemented in a timber harvesting practice under single-tree selection in mountainous forests of Iran where a motor-manual chainsaw is used for felling and a rubber-tired cable skidder is used for log extraction. The average delay-free productivity was 4.55 m3 for felling and 14.73 m3 h−1 for skidding. Lower production costs and higher productivity rates were observed over the gentle slopes and in sunny conditions. The average production costs ranged between USD 4.27 m−3 for felling and USD 5.35 m−3 for skidding. The average emissions ranged between 0.96 kg m−3 for felling and 7.06 kg m−3 for skidding in snowy conditions over steep slopes. The study’s results confirm avoiding harvesting operations on steep slopes (greater than 35%) and in extreme weather conditions to obtain higher work efficiency and to minimize adverse effects of machinery on forest ecosystems. The results should be of use to harvest managers and forest planners considering the application of ground-based harvesting operations using a semi-mechanized system on a range of operating conditions in mountain hardwood stands.

Productivity curve models in eucalypt timber forwarding

Extraction is the most costly and complicated stage of timber harvest operations. The forwarder’s productive capacity in timber harvesting, from planted forests, is influenced by several operational variables, especially by extraction distance and tree volume. Prior knowledge about the effect of these variables on the operation is required for efficient planning. The goal of this research was to model and simulate a forwarder productivity curve for timber extraction in scenarios with different tree average volumes (TAV) and average extraction distances (AED). The research was carried out in a forestry company in the state of Mato Grosso do Sul, Brazil, in clonal eucalyptus stands with TAV varying from 0.186 to 0.310 m3 tree−1 and AED from 0 to 280 m. We performed a time and motion study of the forwarder, following the operation with a DJI-Phantom 4 Advanced drone. Productivity simulations were carried out in different operational scenarios. The models were evaluated using the adjusted determination coefficients (R 2 adj.), standard error of absolute estimate and F-value. Results have shown that as the TAV increased, productivity also increased 14% while the AED presented a relationship inversely proportional to productivity. The highest productivity of the machine occurred in the forest condition with a TAV of 0.31 to 0.36 m3 tree−1 and in the shortest extraction distances. The best-adjusted model explained 46.3% of the machine’s productivity variation. We concluded that TAV and AED variables had a significant impact on the forwarder’s productivity and that it is important to obtain the machine’s productivity curves for efficient forest operations planning.

An Evaluation of Woody Biomass and Pulpwood Market Competition within a Range of Procurement Distances

Abstract In the Southern United States, a rising number of biomass facilities have created new market opportunities for forest landowners, consulting foresters, and loggers, which could increase the competition between the biomass market and pulpwood market for forest biomass. Thus, comparing the profits from conventional roundwood harvesting and biomass harvesting within a range of procurement distances could be crucial to make a harvest decision. In this study, we considered two harvesting systems: conventional and biomass. We developed a decision support tool to predict and compare the final stumpage value from both harvesting systems based on the stand and site conditions, market conditions, and distance to the nearest market. We grew (simulated) loblolly pine (Pinus taeda) plantations to six different thinning ages (12, 14, 16, 18, 20, and 22 yr) at five different site indices (17, 20, 23, 26, and 29 m at a base age of 25 yr) using the PTAEDA4.0 software. Different models were fitted and evaluated for certain training and validating criteria. In both harvesting systems, we select the cube root-transformed model as the best model. Using the models, we predict that the utilization of logging residues and pulpwood as wood chips may yield a higher return to the landowner when the delivered price of the wood chips is comparable to the delivered price of the pulpwood and within the same procurement distance. The selected models thus serve as a decision support tool to inform stakeholders to further maximize their economic return from timber harvesting operations by selecting the most profitable option.

Comparison of Selected Terramechanical Test Procedures and Cartographic Indices to Predict Rutting Caused by Machine Traffic during a Cut-to-Length Thinning Operation

Timber harvesting operations using heavy forest machinery frequently results in severe soil compaction and displacement, threatening sustainable forest management. An accurate prediction of trafficability, considering actual operating conditions, minimizes these impacts and can be facilitated by various predictive tools. Within this study, we validated the accuracy of four terramechanical parameters, including Cone Index (MPa, Penetrologger), penetration depth (cm, Penetrologger), cone penetration (cm blow−1, dual-mass dynamic cone penetrometer) and shear strength (kPa, vane meter), and additionally two cartographic indices (topographic wetness index and depth-to-water). Measurements applying the four terramechanical approaches were performed at 47 transects along newly assigned machine operating trails in two broadleaved dominated mixed stands. After the CTL thinning operation was completed, measurement results and cartographic indices were correlated against rut depth. Under the rather dry soil conditions (29 ± 9 vol%), total rut depth ranged between 2.2 and 11.6 cm, and was clearly predicted by rut depth after a single pass of the harvester, which was used for further validations. The results indicated the easy-to-measure penetration depth as the most accurate approach to predict rut depth, considering coefficients of correlation (rP = 0.44). Moreover, cone penetration (rP = 0.34) provided reliable results. Surprisingly, no response between rut depth and Cone Index was observed, although it is commonly used to assess trafficability. The relatively low moisture conditions probably inhibited a correlation between rutting and moisture content. Consistently, cartographic indices could not be used to predict rutting. Rut depth after the harvester pass was a reliable predictor for total rut depth after 2–5 passes (rP = 0.50). Rarely used parameters, such as cone penetration or shear strength, outcompeted the highly reputed Cone Index, emphasizing further investigations of applied tools.

Effects of Slope Gradient on Runoff and Sediment Yield on Machine-Induced Compacted Soil in Temperate Forests

There has been a severely negative impact on soil water resources in temperate forests caused by the introduction of the type of heavy machinery in the forestry sector used for forest harvesting operations. These soil disturbances increase the raindrop impact on bare mineral soil, decrease infiltration rate, detach soil particles, and enhance surface flow. According to several studies, the role of slope gradient influence on runoff and soil loss continues to be an issue, and therefore more study is needed in both laboratory simulations and field experiments. It is important to define and understand what the impacts of slope gradient in harvesting practices are, so as to develop guidelines for forest managers. More knowledge on the key factors that cause surface runoff and soil loss is important in order to limit any negative results from timber harvesting operations performed on hilly terrains in mountainous forests. A field setting using a runoff plot 2 m2 in size was installed to individualize the effects of different levels of slope gradient (i.e., 5, 10, 15, 20, 25, 30, 35, and 40%) on the surface runoff, runoff coefficient, and sediment yield on the skid trails under natural rainfall conditions. Runoff and sediment yield were measured with 46 rainfall events which occurred during the first year after machine traffic from 17 July 2015 to 11 July 2016 under natural conditions. According to Pearson correlation, runoff (r = 0.51), runoff coefficient (r = 0.55), and sediment yield (r = 0.51) were significantly correlated with slope gradient. Results show that runoff increased from 2.45 to 6.43 mm as slope gradient increased from 5 to 25%, reaching to the critical point of 25% for slope. Also, further increasing the slope gradient from 25 to 40% led to a gradual decrease of the runoff from 6.43 to 4.62 mm. Runoff coefficient was significantly higher under the plot with a slope gradient of 25% by 0.265, whereas runoff coefficient was lowest under the plot with a slope gradient of 5%. Results show that sediment yield increased by increasing the slope gradient of plot ranging 5% to 30%, reaching to the critical point of 30%, and then decreased as the slope gradient increased from 35% to 40%. Runoff plot with a slope gradient of 30% (4.08 g m−2) ≈ plot length of 25% (3.91 g m−2) had a significantly higher sediment yield, whereas sediment yield was lowest under the plot with a slope gradient of 5% and 10%. A regression analysis of rainfall and runoff showed that runoff responses to rainfall for plots with different slope gradients were linearly and significantly increased. According to the current results, log skidding operations should be planned in the skid trails with a slope gradient lower than the 25 to 30% to suppress the negative effect of skidding operations on runoff and sediment yield.