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SEVER Stanislav & HORVAT Dubravko


Croatia's Forest Act, the basic set of regulations covering almost all aspects of Croatian forestry, stipulates that all legal forestry bodies must earmark 0.7% of income for the so-called ‘general forest benefit fund’. About 2.5% of this fund is distributed through the public Croatian Forestry Company for scientific and research projects, and for publishing activities. The remaining funds are mostly used for reforestation of karst terrain and other activities related to biological regeneration. According to 1996 cash flow indicators, the financing of scientific activities compared to the total income from wood sales is as follows:

Figure 1

Figure 1: Financing of scientific and research programmes (1996)

Research programmes for scientific research bodies are financed for a five-year period if approved by the Croatian Forestry Company's Scientific Committee. In the period 1990–95, there were no scientific programmes with specific emphasis on the ecological component, and ecological issues were dealt with by research projects concerned with other issues. Since 1996, two scientific research projects have been launched, each divided into 4 sub-projects. This paper looks at one of these sub-projects on technical aspects of forestry activities with the emphasis on environmental, ergonomic and energy factors: the ‘Development and Use of Environmentally Acceptable Operating Techniques and Technologies’ sub-project. The sub-project was approved by the Croatian Forestry Company's Scientific Committee on the basis of the following considerations:

The use of machinery in all mechanized forest activities and processes carries the risk of causing damage to forest ecosystems, particularly soil compaction, transfer, treading and erosion, in addition to damage to trees and their root systems. Soil is heavily affected in cases of continuous and inevitable contact with vehicles. These negative effects are partly due to technical specifications of machinery that are inappropriate for actual forest land conditions, and partly to inadequate use of machinery. The level of environmental protection can be improved through selection of appropriate machinery and better implementation of adequate technology and organization of working methods.

Various types of machines owned by the Croatian Forestry Company are currently in use in the country's forests: more than 200 crane trucks, approximately the same number of trailers and skidders, almost 500 farm tractors, more than 3,500 motor saws, more than 100 road engineering machines, over 40 motor cultivators, more than 400 different tractor-couplings (including more than 80 mulchers and sprayers), and a variety of other machinery and tools. Knowledge of their properties is essential for their correct use, regardless of their condition — they can be new, adapted, re-modeled or reconstructed. This knowledge must be acquired at the very beginning of the process. Due to the specific requirements of Croatian forestry, some machinery has to be developed independently, and others together with Croatian engineering firms. It is of particular interest to investigate the properties of machine aggregates formed by connecting two machines/couplings; for example, a farm tractor together with a mulcher.

The physical stress of a forest worker performing almost any kind of activity is so high that forest work is rated among the most demanding of activities. The importance of ergonomics in the forest working environment is related to study of the many professional diseases caused by noise and vibration. The impact of noise on the environment is also a significant factor in assessing machinery, and measurement of machinery noise levels is part of almost all international regulations regarding the standard testing of vehicles

Environmental protection related to energy production aims to reduce levels of noxious gases produced by combustion. Increased use of wood to obtain heating energy is a prospect since wood is a regenerative energy source and involves reduced production of noxious gases. Since the basic source of energy for almost all machines is the internal combustion engine, study of its power and efficiency is important. Oil pollution of the soil is also an important factor to be analysed in terms of environmental protection and is a significant indicator for the assessment of machine systems. In addition to environmental, production and aesthetic considerations, it is also vitally important to reduce the extent of forest fires particularly along the Croatian coastline.

Four full-time and three part-time researchers have been working on this sub-project, in cooperation with experts from the Croatian Forestry Company, whose number depends on the scope and location of the research activities being carried out. After deducting the overhead costs of the Faculty of Forestry at the University of Zagreb, DEM 45,000 remains to cover researchers' costs.


  1. The cone penetrometer is the simplest device for measuring soil compaction, but is the least safe due to its sensitivity in measuring soil wetness and a high dispersal rate of measurement results means that multiple repetition of measurement is necessary. Furthermore, deep penetration into forest soil can damage tree root systems, in which the root unit length can range from 200–500 m/m3. The results of soil penetration resistance measurements during the application of mulchers (used for the preparation of stands before acorn falling) are shown in Figure 2, where it is clear that the application of the chosen mulcher-tractor assembly causes compaction of stand soil within the set limits.

    Figure 2

    Figure 2: Penetration during mulcher stand preparation

    Development of a rotational plate penetrometer has begun at the Faculty of Forestry in view of the above-mentioned defects of the cone penetrometer. The first prototype of such a penetrometer is very simple and is shown in Figure 3, along with calibration results and a graph. Shear soil hardness can be measured by the rotational plate penetrometer prototype and the first research results show that it achieves the same results as the cone penetrometer without the disadvantages, indicating that further development in this direction should be encouraged.

    Figure 3Figure 3

    Figure 3: First prototype of the plate penetrometer

    Research into the effect of the tractor trail slope on erosion has been continued in one forest unit and the results over a four-year period (1992–96) indicate that erosion is much greater on steeper slopes. Higher erosion levels are registered where water lies on the trail for prolonged periods of time, when the trail is subject to continuous or occasional water flows, and when trail use is intense. Erosion was slower and more gradual on lesser-sloped trails (1.6% and 14.6%). The volume of eroded soil was 0.07 m3/metre of trail per year, half of which was due to the reduced circumference of pores as a result of soil compaction and shear stress after the passage of loaded vehicles (see Figure 4)

    Figure 4Figure 4

    Figure 4: Erosion measurements on 1.6% and 14.6% sloped trails

    The average loss of soil on a higher sloped trail section (26.1%) was approximately 0.15 m3/metre on a wet trail section and about 0.11 m3/metre on a dry trail section. The most significant erosion occurred during the first year of use, when it stood at 0.36% on a wet trail section and 0.3% on a dry trail section. Analysis of erosion in the last 30 months has shown that it has fallen on the dry trail section, averaging 0.4 m3/metre on a 4-metre wide trail, while on the wet trail section it was still relatively high at 0.07% m3/metre in the last period of testing.

  2. In 1996, a comparison was made of four vehicles use to transport wood in forest stand thinnings: two adapted farm tractors — a Steyr 9078 with a Tigar AD 60E winch and a Torpedo TD75A with an LIV GV 2H 50 winch — and two medium-sized skidders — an LPKT 40 with a ZTS 4t winch and an ECOTRAC with an Igland 3502 winch. Weight and size data for the vehicles were confronted with the morphological characteristics of the skidder family, obtained from data for 92 skidders (see Figure 5).

    Figure 5Figure 5

    Figure 5: Morphological analysis of four thinning tractors/skidders

    Based on the morphological analysis, it can be concluded that from the environmental point of view, the vehicle which had environmental considerations incorporated into the project design stage demonstrated better than expected properties, such as the medium-sized ECOTRAC skidder which could represent a model for an environmentally-oriented and ‘wood-friendly’ tractor.

    The mulcher-tractor assembly was tested in various conditions of low-lying oak forest during the preparation of thinning paths and stands and skid trail restoration. The graph representing the results is shown in Figure 6. These results facilitated definition of the most favourable work regimes, taking stand, energy, economic and environmental criteria into account.

    Figure 6

    Figure 6: Graph representing mulcher-tractor assembly research

  3. Latest data from the Health Protection Department of the Croatian Public Health Institute show that noise and vibration are the most common causes of professional diseases in the country. (see Figure 7). It should be noted that Croatian forestry ranks second in terms of numbers of registered industrial invalids.

    Figure 7

    Figure 7: Breakdown of professional diseases

    Ergonomic testing of the performance of the medium-sized ECOTRAC skidder has been completed, with regard to the relationship between the operator and environmental noise pollution. The results of one test and a graph representing measurement for surrounding noise are shown in Figure 8.

    Figure 8

    Figure 8: Results and graph of surrounding noise measurements

    In 1977, thanks to the efforts of the research team on this sub-project, the Laboratory for Noise and Vibration Measurement at the Faculty of Forestry became the first body to be certified in the field of forestry measurement in Croatia, after the Ministry of Labour and Welfare had approved the standards of the laboratory's technical equipment and the competence of its staff in compliance with Safety at Work Act. This certification is the most direct acknowledgement of the efforts of the staff of the Croatian Forest Company and the Faculty of Forestry to equip the laboratory, train its operators and convert acquired knowledge into procedures and regulations.

    The continuous electrocardiography (24-hour ECG) method was used to test the physical stress of tractor drivers while pulling wood with 45 KW Zetor 7245 and 60 KW Zetor Crystal 8045 types of tractor. During the tests, drivers remained in their normal settings carrying out their daily routines. Recording was effected by a portable electrocardiorecorder, the Avionics model 445 (for results, see Figure 9). The results of the ECG analyses show that the highest pulse rate was recorded at different time intervals, most frequently during the work shift, but also outside work. The highest pulse rate values recorded during work account for 69–98% of all high pulse rates recorded, and the period in which the highest pulse rates were found was typically during the second phase of the work shift, between 10 a.m. and 3 p.m.

    Figure 9

    Figure 9: Worker with electrocardiorecorder and graph of pulse rates

    Based on the first results, the 24-hour ECG method has proved to be a valuable supplement to traditional methods for testing the physical stress of forest workers and it opens up new possibilities for organising and assessing forestry work.

  1. Interest in the energy aspects of forest production were focused on increasing the share of biomass produced for industrial needs and for consumption by the people. Analysis of energy content, consumption, sources and problems, etc. were common features of research work in 1996. For example, in a modern 1 MW biopower plant in a forest unit in the district of Gorski Kotar, data on wood trash consumption were gathered, the temperature was measured every day at 1 p.m., the wetness of wood chips was determined, chipper performance was monitored and the chemical composition of the most frequently used wood analysed. Findings showed that the energy consumption required for the production of firewood is much less than the energy that can be obtained from these wood products (see Figure 10). These results reinforce the need to develop regenerative energy sources.

    Figure 10

    Figure 10: Energy consumed for obtaining wood and the energy wood can provide

  2. Research into fire road construction is particularly significant, since this year alone, in the coastal area of the country, more than 1% of the forest stand was lost to fire (see Figure 11).

    Figure 11

    Figure 11: Area burnt and number of fires in Croatia (1992–97)

    Between 1991 and 1998, 2,143 km of forest fire lines (1,813 km of forest fire roads and 230 km of forest fire lanes) were built. Taking into account fire brigade requirements and carefully modifying them in line with the maximum allowed density of forest fire roads in an ecosystem, as well as consulting domestic and overseas reference material related to the question, limits were set for the openness of karst forest necessary. This density between 15 and 34 m/hectare, although precise values are determined by investigating all related factors in a given area.



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