The paper deals with the characteristics of three different types of power train hybridization of forest logging machines and with the benefits of reducing environmental impacts by comparing new technology with more conventional, older technology. New hybridization options that could be implemented in forestry machines are also discussed. The paper divides a hybrid solution into three classes based on the energy used in the system of hybridization. First is an electro-hybrid system that uses an electric motor and battery or different storage device. The second, a hydraulic hybrid system, is a solution with a hydraulic accumulator, hydraulic motor, and pump. The third system is a combination of the electro-hybrid and hydraulic-hybrid system. The current technical and technological development of hybrid drive systems, as well as their components, has led to significant improvements in drive performance and thus better performance of the new generation of forest vehicles. Improved energy efficiency using hybrid propulsion systems in forest vehicles would result in a significant reduction in greenhouse gas emissions and possibly lower maintenance costs.

For the needs of fuel consumption analysis, a database for a period of 2 years was created for three types of skidders operating in two different management methods—even-aged and selective forests. A total of 436 skidders were processed in the database, of which 255 skidders worked in even-aged forests and 181 skidders worked in selective forests. The average consumption of skidders in even-aged forests ranged from 1.38 to 1.65 L/m³ or from 7.81 to 9.34 L/PMH, while in selective forests, the average consumption ranged from 1.06 to 1.34 L/m³ or from 6.49 to 7.10 L/PMH. The obtained results indicate higher fuel consumption for all three types of skidders in regular forest management. There is no statistically significant difference in fuel consumption between the studied skidders. Comparing fuel consumption in L/PMH, we notice that there was an increase in fuel consumption in relation to the age of the skidder.

During forest harvesting operations, exhaust emissions from forest vehicles are released at different levels depending on several variables. This pollution released into the atmosphere is considered one of the main anthropogenic factors that negatively affect forest ecosystems. In this study, we analyzed exhaust emissions from a skidder diesel engine during various engine loads. Measurements were done on an ECOTRAC 140 V skidder with the water-cooling diesel engine and a built-in catalyst with an SCR system. The composition and amount of exhaust gases (CO, CO₂, O₂, NO_x,) at different loads of the diesel engine of the skidder and engine temperature were measured using a MAHA MET 6.3 measuring device. The amount of exhaust gases was analyzed in relation to the engine speeds, engine temperatures, and the European emission standards for engines used in nonroad mobile machinery (NRMM). Influences of catalyst systems and recommendations for more environmentally friendly forest harvesting practices are addressed. With the engine unloaded, the amount of CO₂ increased when engine speed was increased, while other amounts of exhaust gas decreased. During the cold start, the concentrations of hydrocarbons and nitrogen compounds were high. The composition of the exhaust gas was affected by the exhaust reduction system installed in the tractor and the amount of the exhaust gas was dependent on the engine load. The skidder engine met the requirements of the exhaust gas standards EPA/COM IIIB Tier 4 (I) under which it is declared. With a load engine during winch operation (2300 rpm), NO_x amounts mostly exceed the limit values of the standard. Exhaust emissions can be reduced at various operating levels by utilizing the most environmentally friendly technologies and following the correct procedures, such as warming the engine up to operating temperature prior to operation and operating in the most favorable mode with optimal speed. The regular reduction of exhaust limit values to newer stages of the standard therefore leads to the continuous development of engines and forest vehicles in general.

The increasing importance of utilizing new technologies, such as GNSS (Global navigation satellite system) devices, total stations, drones, scanners, etc., in forestry has become evident with the development of these tools. Combined with precise GNSS devices, UAVs represent an efficient tool that facilitates field measurements and reduces time spent in the field while also providing highly accurate data. To accurately determine the application of spatial data for calculating the longitudinal slope of forest/logging roads in a research project, measurements based on UAVs were conducted and compared with GNSS data. GNSS data were considered the reference values for the studied area, assuming that satellite positions and internet signals were good. An accurate longitudinal slope was necessary to define fuel consumption on forest/logging roads and slopes throughout the project and to verify the calculation method that could be applied for such or similar terrain conditions and overgrowth. The main goal of this research phase was not to study fuel consumption but to obtain an accurate longitudinal profile of forest/skid roads on rocky terrain that is not overgrown or poorly grown. The study put forth two hypotheses, one of which was ultimately confirmed, while the other was refuted. The results show no significant differences when comparing the absolute elevation of the points in the profiles for defining the longitudinal slope of the road using the program for designing forest/skid roads. While applying such a method of data collection to create the main projects for the (re)construction of forest/skid roads, there are significant deviations in earthwork masses. There was a difference of over 22.64% in one of the types of earthwork excavation on the designed forest road, so the method implemented in the research does not give sufficiently accurate results.

Growing demand for forest machines that cost less to operate than current compared to traditional hydraulic and mechanical ones, along with regulatory pressures for lower emissions, is increasing manufacturers’ interest in developing electric and hybrid drives. While purely electric drives of forest machines meet a lot of bottlenecks (costs of the electric components, battery durability, duration of charging, access to the electrical grid, size of batteries that can ensure enough energy for 8 h working time), electric hybrid drives offer a favorable solution for the propulsion of forestry machinery in terms of lower fuel consumption and improved efficiency. Among all forest vehicles, specialized forest tractors (skidders), so far, have not been considered for forest vehicles with hybrid drive capabilities. A skidder is a forest-articulated self-propelled vehicle for pulling trees or parts of trees. In most countries in southern Europe, the use of skidders equipped with forest winches is the most common technique for timber extraction. The first goal of the research is to develop methods for measuring the energy consumption of skidders at different operating tasks and under different field conditions. Research was performed on the skidder Ecotrac 140V (from Croatian producer Hittner Ltd.) during timber extraction in mountainous terrains in Lika–Senj County. The skidder was equipped with a measuring device WIGO-E (Telematic Data collector) gateway with an integrated GPS system, which ensured data were collected from sensors and motor and stored in a computer via CANBUS and data transfer with GSM to Web platforms. Additionally, a fuel-flow meter was installed on the skidder. Data on fuel consumption (mL), position (traveling route), detection of winch work, engine rpm (min⁻¹), engine torque (% of max), throttle position (%), and engine temperature were measured with a sampling frequency of 5 s. Furthermore, skidder load volumes per cycles and slopes of tractor paths were constantly measured. The paper shows the skidder’s energy consumption per day, work cycle, and individual work procedure with regard to the size of the load, the slope of the tractor path, and the direction of movement based on overlapping and merging all measurement data. Using mathematical and simulation models of the drive with defined operating cycles obtained by measurement, the possibilities of the hybrid drive and the dimensions of the elements of the hybrid drive (internal combustion engine, electric motor, batteries, control unit) were determined and are presented in this paper.