In timber trade in Croatian forestry, roundwood is usually dispatched by volume in accordance with the standard (EN 1309-2: 2006) and there is a loss of volume due to the prescribed ways of measurement: 1) length, 2) mean diameter, 3) deduction of bark and 4) the expression for estimating the volume of roundwood. Impact analysis of transported load (actual timber volume, timber mass, reduced volume due to the prescribed measuring) for Valmet 840.2 forwarder productivity in relation to the transportation distance was determined using a multi-criteria productivity forwarder model (Stankić et al. 2012).

The study was based on five different loads of oak (Quercus robur L.) in a forwarder, which differed with respect to: 1) the type of loaded assortments (roundwood, firewood, mixed load), 2) amount of loaded timber (full height of loading area, <2/3 height of loading area, <1/3 height of loading area of the vehicle). In addition to weighing (aimed at determining the load mass), measurement of timber in the load was also performed including as follows: 1) measurement of length to centimeter accuracy, and 2) measurement of diameters on the thicker and thinner end and in the middle of logs. The actual (gross) volume of each log was calculated using Reicke-Newton’s formula, and the net volume of timber was calculated in accordance with the standard (EN 1309-2: 2006).

Differences in forwarder productivity, expressed in terms of timber gross volume and load mass are negligible (<1%) due to the effects of wood density 995.8 ± 2,5 kg/m³.

Forwarder productivity expressed in terms of timber net volume ranged from 3.5% to 24.3% when compared to the actual timber volume. The obtained results depend on the type and size of loaded assortments and quantity of loaded timber.

Obviously, the transport of timber and trade of timber are two different concepts from the standpoint of timber volume or load volume, with a different impact on the participants in the timber supply chain.

Keywords: prescribed measurement of roundwood, mass, volume, forwarder

This article presents the results of a research dealing with operating efficiency of articulated and tractor assemblies in the plots of poplar plantations in which different means of work were used for felling and cross-cutting. The aim was to study the effects of the arrangement of wood assortments on the driving speed of the vehicle, the time needed to load and manipulate the vehicle and the overall working efficiency of forwarders. The research was carried out in Vojvodina, in the area of PE »Vojvodina šume«. Altogether 170 transport cycles were recorded and 2166.73 m3 transported. The research results show that the forwarder moved faster on the felling site where the felling and cross-cutting operations were carried out by a harvester. The speed was 10% higher and it took 5% less time to load the forwarder. The differences were considerably greater concerning the manipulation time (maneuvering and positioning the vehicle during the loading). The driving speed decreased with an increase in the load volume. Fuel consumption was lower in the felling site where a harvester was used for felling. Under the same working conditions, the tractor assembly achieved better productivity because it drove at considerably higher speeds. The differences in the average load volume were not so great, which significantly affected the productivity of the tractor assembly. The initial hypothesis that a forwarder achieves better working efficiency in the felling site, where a harvester has been used in the operations of felling and cross-cutting, was confirmed.

Keywords: John Deere 1210E forwarder, tractor assembly, first phase of transport, poplar technical roundwood, efficiency, costs

Soil disturbance, as a result of the movement of forest vehicles, has a negative effect on the growth and increment of forest trees and hence should be kept at a minimum. Some of the measures for reducing soil disturbance are: selecting a suitable harvesting system, setting a skid trail network (with traffic surveillance) and oriented felling as a must. This paper presents the soil disturbance in timber forwarding on two adjacent felling sites after the final felling of common oak. The investigated forwarder was equipped with Fleet Management System (FMS connection) that enables remote control of its work or its position while moving in the researched felling sites. The results indicate that the site disturbance of the researched felling sites is too high (>30 % of cut block areas) and that by better work organization, soil disturbance can be reduced to an acceptable level.

Keywords: soil disturbance, forwarder, lowland forests, work organization, secondary opening

This paper presents the research results of the efficiency of timber (broadleaves) extraction by skidder, using a modified half-tree length method with crown parts in thinning beech stands in the Republic of Serbia. The effectiveness of this method is assessed by quantitative and qualitative indicators. The modified method has been developed with the goal of using forest residues (unprocessed wood) in hilly and mountainous areas of the Republic of Serbia. This modified half-tree length method of broadleaves with crown parts resulted in an increase of 8% of the volume of timber extracted to the road landing when compared to the assortment method. Stand damages caused to the remaining standing trees after felling were not much higher than damages caused by using the assortment (CTL) method. With this proposed modified method, the extraction of one-meter fire-wood can be carried out without using horses (derrick method).

Keywords: method of wood processing, hilly-mountainous conditions, beech, forest residues, tree damage.

Investigation of different skidding methods was done in the northwestern part of the Republic of Srpska, in the area of municipality of Ribnik. Two skidding methods were compared, assortment (short-log) method and half-tree length method. Investigation was conducted in four sample plots, in two compartments of beech forests. The difference between sample plots was based on working methods and mean DBH of felled trees. The aim of this research was to compare the productivity and costs of assortment method, which is currently dominant in the forestry of the Republic of Srpska, and half-tree method as a modification of tree length method. Skidding was done with forest skidder LKT 81T in winter conditions with almost no snow. Time and work study was performed. Different statistical methods were used for investigating the influence of different variables on the work process. Multiple linear regression analysis showed that work operations mainly depend on distance and load volume in both methods. Loaded drive depends on distance and load volume. Strength of correlation relationship is similar in both methods. These findings are in compliance with other investigations that can be found in literature. The results showed higher productivity and lower costs in half-tree-length method than in the assortment method. For the skidding distance of 250 m and similar stand conditions, the productivity is 42.29 m³/day for assortment method (A1) and 50.50 m³/day for half-tree length (A2) method, and 62.93 m³/day (B1) and 83.64 m³/day (B2), respectively. Costs are 17% (A2 against A1) and 40% (B2 against B1) lower for half-tree length method when all other conditions are the same. The difference in cost increases with the increase of the difference of the average piece volume of the two skidding methods.

Keywords: tractor skidding, harvesting methods, work study, cost calculation, B&H

The optimal forest road network must be established through the following work phases: planning, designing, construction with supervision and maintenance/repair (Pentek et al. 2004). In addition to these obligatory phases of forest traffic infrastructure optimization, another two work phases are included occasionally: reconstruction phase and phase of road removing/restoring.

Good planning is necessary in forestry as well as in timber harvesting and forest opening, considering the diversity of Croatian forestry in terms of terrain orography (lowland, hilly, mountainous and karst region), site and stand characteristics and forest management practices (regular, selective), different patterns of forest road network (road network layout) and different levels of road density. Responsible planning of forest roads is a guarantee of rationalization (a set of procedures to achieve cost reduction) in a part of forestry production.

Due to the level of planning, its complexity, planning period and operation area, planning of forest roads can be divided into three levels:

• Planning of forest road network at state level or relief area level (lowland, hilly, mountainous and karst relief region). This is the highest and initial level of planning (global planning – strategic planning),
• Planning of forest road network at management unit level – represents an intermediate level of planning (general planning – tactical planning),
• Planning of a specific forest road – result of tactical planning leads to planning at the lowest level (local planning – operational planning), followed by design phase.

Planning of forest roads on strategic level (the highest level) must define as follows: relief areas considering measurable terrain and stand characteristics together with forest openness, and its analyses; develop guidelines for appropriate models of primary and secondary forest opening in different relief areas (road layout/pattern); develop guidelines for appropriate and achievable harvesting systems in different relief areas (considering stand characteris¬tics and existing (present) road density).

The objectives of this study are:

• classification of Management Units (MU) and Forest Administrations (FA) into relief categories,
• identification of existing primary openness by MU, FA and relief categories,
• calculation of length of the planned forest road network per FAs and relief regions, for achieving planned (targeted) primary road density,
• cost calculation of the planned forest road network, per FAs and relief regions, for achieving planned (targeted) primary road density,
• proposing guidelines for further opening of Croatian forests.

The study was done in 16 Forest Administrations within the company »Croatian Forests« Ltd. Zagreb.
Planned primary values of openness at the level of relief categories are guidelines to be followed, but in the final design of primary forest road network they should not and must not be rigidly observed. It is recommended to review and, where necessary, redefine values of the planned primary classical openness by relief areas, taking into consideration all the factors that influence the calculation of the planned density of primary forest transportation system.
At the level of tactical planning, possible deviations from the strategic level are possible, in both positive and negative values, but within reasonable intervals.
Based on the analysis of the existing primary road density in the study area (by FAs and by different relief areas) as of December 31, 2011, it is concluded that the planned primary road density has not been achieved in most of the state forests. Moreover, in a majority of state forests not even minimal necessary primary road density has been achieved, which has a negative impact on the quality, efficiency and rationality of managing these insufficiently opened forests.
The time period for achieving the intended values of primary road density should be extended, while simultaneously the construction of forest roads on an annual basis should be intensified. The financial, technical and infrastructural capacities of the company »Croatian Forests« Ltd. Zagreb should also be taken into account. In addition to the existing sources of funding, funding from current operations and funds from non-market forest values, as well as other possible sources of funding (for example EU funds) in all phases (obligatory or not) should be provided in order to create an optimal primary forest road network.

Keywords: truck forest roads, secondary forest roads, road network planning, designing of forest roads, construction of forest roads, road network maintenance

Forest roads should be in a condition to bear traffic load at every moment. They can endure traffic load only if their dimensions are within the limits prescribed. The dimensions of forest roads depend on: the soil type, category of forest road, and vehicles that use them. In this paper, forest roads constructed on two types of substrates (terrain category 3 and 4; Protić 1970) were observed, and dimensions of horizontal and vertical alignments of forest roads were determined. According to the results of this research, it was concluded that the state of forest roads is satisfactory in terms of traffic. However, it is necessary to pay attention to longitudinal slope of forest road carriageway and cross slope of carriageway in the curves that depend on the longitudinal slope of carriageway and radius of horizontal curve.

Keywords: forest roads, horizontal and vertical alignments, longitudinal slope, cross slope of carriageway

Timber haulage is the last phase of wood harvesting. Due to its characteristics, cycle operation, a lot of unloaded driving, high purchase price of truck units, transport of small amounts of cheap goods, high oil prices, high fuel consumption, timber haulage is most expensive phase of wood harvesting. Apart from high prices, timber haulage has a lot of negative impact on environment due to its high greenhouse gas emission.
The aim of this paper is to analyze the data of the total amount of transported timber, fuel consumption per tonkilometer, which is the finest indicator of energy consumption of transport, and to analyze greenhouse gas emission per production unit for all truck and trailer units owned by »Hrvatske šume« Ltd. (HŠ) in 2012. Furthermore, the obtained results have been compared with the results of fuel consumption given by Anić et al. (1996).
In 2012. »Hrvatske šume« Ltd. owned 101 truck and trailer units of different types (Fig. 1). In the analyzed year, their truck and trailer units transported 842,776 m³ or 17.47% of all produced wood assortments. The rest was transported by private companies (74.65%), and by local population (7.88%). For transportation of 17.47% of wood assortments, trucks owned by HŠ consumed 2.25×106 L of fuel and they traveled 3,499,901 km. Some research parameters are shown in Table 3. It is interesting to see that the range of backhauling was from 34.2% to 57.3%, with an average of 47.6%.
Fig. 2 shows the annual productivity of truck and trailer units owned by HŠ. Fig. 3 to 5 show fuel consumption of all analyzed truck and trailer units, distributed in 13 administration units. Fig. 3 shows fuel consumption per unit of transported wood. The average fuel consumption was 2.73 L/m³, the maximum fuel consumption was 3.9 L/m³, while the minimum was 1.26 L/m³. Fuel consumption per traveled kilometer was between 0.46 and 0.94 L/km with an average value of 0.66 L/km or 66 L/100km (Fig. 4). Figure 5 shows fuel consumption per ton-kilometer. Values were from 0.04 to 0.16 L/t km.
The calculated average unit fuel consumption of 2.73 L/m³ is higher by 0.4 L/m³ than the consumption given by Anić et al. (1996). The reason for this higher consumption probably lies in stricter control of maximum allowed axle loads and total mass of truck and trailer unit, which results in lower amount of timber transported in one cycle. Furthermore, difference stems from different engine power of trucks used in 1996 compared to trucks used in 2012.
Based on values of emission factors showed in Table 2 and unit fuel consumption, we calculated greenhouse gas emission of truck and trailer units owned by HŠ. The emission values are showed in Table 4. Total greenhouse gas emission emitted from timber haulage in Croatian forestry (TTU’s owned by HŠ and private contractors) is 31.88 Gg. This value is only an estimate, and the real value is to be determined. It is expected that emission will decline in the future, because in 2012 HŠ owned only 4 truck and trailer units, which meets the requirements of EURO V norm.
Due to its characteristics, timber haulage has a negative impact on the environment and very low energy efficiency. Fuel consumption has a great impact on total timber haulage costs and therefore also a great impact on wood harvesting costs.
To improve timber haulage and decrease fuel consumption and greenhouse gas emission, it is necessary to conduct a detailed survey of timber haulage using Fleet Management System, and to determine with direct measurements the exact fuel consumption, both total consumption and consumption by working procedures. It is also necessary to measure GHG emission, and utilization of truck and trailer units. Furthermore, it is needed to determine the effect of driver behavior on fuel consumption, as well as the effect of forest road conditions on fuel consumption. Besides the implementation of FMS system and new organization solutions, it is needed to find new technical solutions (e.g. install dismantling crane, electric propulsion of hydraulic pump for crane drive), with the aim to increase energy efficiency, decrease negative impact on the environment and increase utilization of timber haulage.

Keywords: timber haulage, truck and trailer unit, fuel emission, greenhouse gas emission

This paper presents the investigation of five (5) characteristic forestry species (Fagus ×moesiaca (K. Malý) Czeczott, Quercus petreaea (Matt.) Liebl., Quercus pubescens Willd., Carpinus orientalis Mill., Pinus nigra J. F. Arnold) that cover the major part of the total forest area, and account for around 70% of the total forest reserve in the Republic of Macedonia. These forestry species are also very common in other regional forests.

The purpose of this investigation is to establish the energy value of these species at different trunk height and different parts of the tree (wood, bark) in order to determine the differences due to different cell structure.

The material for this investigation was collected in different regions of the Republic of Macedonia, and for each investigated species the material was collected at two different locations with different ecological conditions. Wood density parameters of tree species were also established for local conditions, and combined with the available sources from other countries. The article presents a harmonized approach to estimate the potential for energy production by different species, eliminating different ecological growing conditions.

The results of the investigation show that the conifers have higher energy value than broadleaved species, and that this difference is significant. There were no significant differences in the energy potential between different parts of the tree (1.3 and 5.3 m, branches), except for the bark. The energy potential of the selected species is significant, and with certain technological changes in the phase of forest utilization and in the process of transformation of wood into other kinds of energy (heat, electric, etc.), it is a significant basis for the improvement of the energy balance of the Republic of Macedonia, along with the use of the alternative, renewable and environmentally friendly energy.

Keywords: biomass, calorific value, alternative energy