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 paper presents the method of calculating planned prices of timber harvesting operations, which are the subject of public tenders in the forest management company Hercegbosanske šume Ltd. Kupres and the analysis of deviations of the planned from the contracted (realised) prices for timber harvesting operations in 97 groups of compartments, which were the subject of public tenders in 2019 and 2020. Descriptive and correlation statistical analysis also included stand and terrain indicators in groups of compartments in public tenders: area, net volume of marked trees, harvesting density, number of marked trees per hectare, volume of medium marked tree, slope, average timber extraction distance, terrain stoniness and parameter of uphill timber extraction. The test of dependent data pairs indicated that there is a statistically significant difference between planned and contracted prices of timber harvesting operations (
t
= 7,78,
p
< 0.001), and the results of correlation analysis confirmed the connection of influential factors of forest operations with the contracted and planned timber harvesting prices. Due to the statistically significant (
p
< 0.05) and very strong correlation with the contracted and the planned price of the timber harvesting operations calculated by the presented method, the dependence was equalized by a linear regression model with a coefficient of determination of 0.667. In conclusion, the method of calculating the planned price of timber harvesting operations is a good predictor of what can be contracted prices in public tenders thus showing its suitability in future calculations. Weak and negative correlation (
p
< 0.05,
r
= -0.22) of the difference between the contracted and planned price of the timber harvesting operations on the volume of the medium marked tree, indicated future monitoring to determine its causes, which could be: 1) mutual competition between timber harvesting operations providers with a larger volume of medium marked tree or 2) overestimation of the volume of medium marked tree in the presented model. Guidelines for increasing the accuracy of determining input parameters (average timber extraction distance, slope, terrain stoniness, and parameter of uphill timber extraction) are also presented. Given that the calculation is related to the average planned price at the level of forest management, which is determined by the management of the company, it is necessary to constantly monitor the market in order to react in time if major oscillations occur.
Background and Purpose: Terrain trafficability and vehicle mobility during timber extraction are highly influenced by terrain characteristics, as well as by soil bearing capacity. Insufficient ...planning, too heavy vehicles, excessive traffic, poor soil knowledge, together with bad weather conditions, cause severe disturbance to forest soil. Damage to the forest ecosystem arises due to felling and timber extraction operations, regardless of the technical means used in this process. Traffic intensity plays an essential role in soil compaction because deformations can increase with the number of passes, which may lead to excessive soil disturbance.
Materials and Methods: The research was conducted in Zalesina, a hilly and pre-mountainous part of Gorski kotar, Croatia, in two management units (MUs) comprising of 569.64 ha of selective beech and fir forests. Physical and mechanical properties of forest soil, essential for vehicle mobility and terrain trafficability during timber extraction are based on measuring the following soil parameters: 1) soil penetration resistance, 2) soil shear strength, and 3) current soil moisture. Measurements were made during one calendar year, on five sampling plots (three in MU "Belevine" and two in MU "Kupjački vrh") chosen on the prevailing soil types in both MUs.
Results: The highest values of cone index and shear strength were recorded in July which was the warmest and driest month with only 7 rainy days. Current soil moisture was the lowest in July at φ=15.26% vol, while the lowest values of cone index were from October to January with precipitation at its climax from September to January with cumulative 1232 mm of rain and 846 cm of snow. Lower values of penetration resistance were in MU "Kupjački vrh" at 0.96 MPa, which is related to overall terrain structure of high karst and surface roughness, making the sampling of plots difficult. By comparing cone index values (CI15) and the mean values between 5 and 25 cm of depth (CI5-25), the variation coefficient indicates a lower variability of CI5-25 values on four out of five sampling plots. However, t-test showed no statistically significant difference between these soil parameters.
Conclusions: Data regarding soil bearing capacity in a map form as an additional layer to other maps of stand characteristics would ensure better opportunities for planners or operators to reduce and avoid rutting and soil compaction. Measured data on penetration resistance, soil shear strength and current soil moisture have not only given in a simple and a fast manner the in situ stand conditions, but they have also shown their dependence on climatic conditions.
This paper presents the research of possibilities of forwarding timber in an efficient and environmentally friendly way, under conditions of limited bearing capacity of gley soils of Croatian lowland ...forests due to their increased moisture all the year round. Reduced soil bearing capacity causes restricted mobility and decreases the forwarder productivity, and also increases the level of damage caused to forest soil, reflected in its compaction and rutting (Fig. 1).In lowland even-aged forests of Croatia, main felling is mostly carried out based on wood cutting and processing by chain saws and forwarding of timber, processed by cut-to-length method, by six-wheel forwarders, usually not equipped with semitracks on rear wheels of bogie axle (Fig. 1).The analysis was carried out on the example of a medium-weight six-wheel forwarder Valmet 840.2 (nominal load capacity of 12 t, whose dimensions and load distribution of empty vehicle are shown in Fig. 4), and this analysis involved as follows: 1) the effect of load reduction on forwarder efficiency, 2) forwarder environmental soundness under conditions of limited soil strength based on nominal ground pressure (Mellgren 1980) of front and rear wheels of the vehicle depending on the mass of loaded timber, vehicle with narrower (600 mm) and wider (710 mm) tires, or with tracks on wheels of the rear (bogie) axle. The limit value of environmental soundness would be the allowed ground pressure of limited bearing capacity <60 kPa (Owende et al. 2002).The effect of load reduction (4 t, 8 t with respect to 12 t of the vehicle nominal load capacity) on forwarder efficiency with respect to the distance of timber forwarding, is expressed according to the multicriteria calculation model of productivity of these vehicles (Stankić 2010), which takes into account: 1) forwarder class 2) soil strength, 3) use of tracks, 4) felling density, 5) volume of the average felling tree and 6) distance of timber forwarding. The unit cost of timber forwarding was calculated according to machine rate made by the company »Hrvatske šume» d.o.o Zagreb for the forwarder Valmet 840.2 (433.19 kn/h).For calculating the nominal ground pressure (Fig. 3), a theoretical model of axle load distribution was used, the case of vehicle at standstill on level ground, depending on mass and length of loaded logs in the bunk area of the forwarder (Poršinsky and Horvat 2005). The analysis of axle load distribution was based on an average length of logs (4 m) made by cut-to-length method in the area of the Croatian lowland forests, and the mass of 1800 kg of a pair of semitracks. The wheel load assumed even load distribution of axle load by pertaining wheels. The contact area between wheels (tracks) and soil was calculated according to Mellgren (1980), for narrower (front – 600/65-34, rear – 600/55-26.5) and wider (front – 710/55-34, rear – 710/45-26.5) tires recommended by the manufacturer of forwarder.The analysis of the forwarder environmental soundness was based on: 1) values of nominal ground pressure of front and rear wheels of the vehicle depending on the mass of loaded timber, and use of narrower and wider tires, i.e. or use of tracks, and 2) the upper limit value of the allowed ground pressure (<60 kPa) of limited bearing capacity (class 3 – Fig. 2), which prevails at the time of main felling in the Croatian lowland forests.The results of efficiency analysis of timber forwarding (Fig. 5) showed that the reduction of load under conditions of limited bearing capacity of gley soils, as a measure for providing vehicle mobility as well as for diminishing the level of damage caused to forest soil, is highly unacceptable due to the decrease of productivity and increase of unit costs.The analysis of nominal ground pressure (Fig. 7) under wheels of the front axle and wheels (tracks) of the rear axle, showed that under conditions of limited soil bearing capacity: 1) the forwarder nominal load capacity may be used and that efficient timber forwarding may be performed, 2) the environmental soundness can be provided by the application of four-axle (eight-wheel) forwarders equipped with wider tires and half-tracks on wheels of front and rear bogie axle of the vehicle.These results should be used as guidelines for purchasing forwarders, and such approach would provide in future ecoefficient timber forwarding under conditions of limited bearing capacity of gley soils in main felling sites of lowland forests.
In the area of Croatian lowland forests, forwarders are usually used for extraction of timber assortments. Within the project »Systematization of norms for the production of timber assortments«, ...which was financed by the state company »Hrvatske šume« d.o.o. (»Croatian Forests« LLC), the process of development and implementation of new productivity norms for forwarders was carried out. Initially, for the execution of the research, it was necessary to gather data about technical characteristics of forwarders most frequently used in Croatia, but also around the world. The morphological analysis was performed and it was the basis for the classification of forwarders into classes. Three classes of forwarders were obtained after cluster analysis and load capacity appeared to be the most important factor. Machine performance was evaluated on 30 research sites. The standard method of time study (snap-back chronometric technique) was used. During the recording process, data of factors influencing forwarding (stand and terrain conditions) were collected. After analyzing the collected data, it was determined that the forwarding productivity depends on the forwarder class, average extraction distance, load characteristics, terrain and stand conditions. Regression analysis was used for identifying the time consumption of individual work components, and the productivity model for forwarding was developed. The obtained model was implemented into the application HsPPI. This is a part of the information system developed by IT Department of the state enterprise »Hrvatske šume« d.o.o. and is used for production planning in timber harvesting. The system is based on dBase IV databases and two main program modules. The main parts of the system are: tree marking data, assortment structure plan, production plan (felling, processing and extraction) and sales plan. Within a part of the production plan there is a module for calculating productivity norms for timber forwarding.
Soil Characteristics in Oak Lowland Stand Đuka, Andreja; Popović, Maja; Poršinsky, Tomislav ...
Croatian Journal of Forest Engineering,
01/2024, Volume:
45, Issue:
1
Journal Article, Paper
Peer reviewed
Open access
The behavior of the vehicle-soil interaction and reduction of the possible soil damage to an acceptable level is one of the goals of forest engineering. This study aimed to analyze the impact of a ...6-wheeled forwarder on water-physical soil characteristics on lowland soil – pseudogley. The research was conducted using a 17-ton Timberjack 1710B forwarder, which forwarded 694.1 m3 volume of oak (Quercus robur L.) assortments. Soil characteristics were measured after each of the eight passes of the loaded forwarder. Bulk density measured on the surface layer ranged from 1.01–1.23 (Me=1.10) g/cm3 (undisturbed soil); 1.14–1.70 g/cm3 (multiple passes of the loaded forwarder). The highest soil density increase was observed after the first pass of the loaded forwarder (16%). Soil solid phase ranged from 2.49 to 2.73 g/cm3 with no statistically significant difference between undisturbed soil and soil after multiple passes of the vehicle. The highest porosity decrease was observed after the first pass of the loaded forwarder (10%). The highest soil water retention capacity decrease was observed after the first pass of the loaded forwarder (3%). The highest soil air capacity decrease was observed after the first pass of the loaded forwarder (30%) compared to the undisturbed soil of the forest stand.
The aim of the research was to determine the productivity of the cable skidder Timberjack 240C equipped with double-drum winch Konrad Adler HY 16 during skidding of fir roundwood from the Croatian ...mountainous selective forests of fir and beech. The research took place in the area of Delnice Forest Management, at two workplaces with different degrees of stone obstacles provided with strip road network. Skidder productivity was determined by the method of time and work study. The paper shows the results of some working characteristics of the researched skidder, such as: travelling speed of unloaded and loaded skidder, time consumptions of felling site work (loading) and roadside landing work (unloading), allowance time, realized load volume, fuel consumption, dependence of possible productivity and costs per unit on timber skidding distance.
This paper presents the history and tradition of forestry academic education in Europe. In the last few decades a lot of changes have occurred and forestry academic education has lost a high-level ...position in European society and economy. In many European countries, higher education forestry programs are just a part of the educational system of universities of applied sciences, life sciences, agricultural or technical sciences. Important changes of higher education systems have been made with the establishment of new educational programs according to the Bologna principles. Some problems and disadvantages will be discussed on the Croatian example, where the reform of teaching programs according to the Bologna process was made 7 years ago. The most important problems are related to the employment of bachelors of forestry, decreasing number of students, and evaluation of forestry educational programs in forestry practice. Also the field of forest engineering, which still has a quite strong position in forestry practice, is not adequately present in teaching programs in many countries. In order to provide the place that belongs to higher forestry education in the Republic of Croatia and Europe, the existing study programs should be revised and updated with the development of new teaching methods, promotion of new and updated teaching materials and handbooks, encouragement of students for scientific and individual work. With the aim to preserve and recognize the importance of education in the field of forest engineering, some existing principles of Bologna process could be accepted. First, the need should be stressed for the development of joint master studies in the framework of Erasmus Mundus program, which would strengthen the existing cooperation and serve as the basis for a more fruitful scientific-research and educational work. It needs to be pointed out that the establishment of new graduate studies in the field of forest engineering would contribute to the development of higher education in the European environment, with an aim of providing student and academic staff mobility.
DTM models to enhance planning of timber harvesting Djuka, Andreja; Porsinsky, Tomislav; Vusic, Dinko
Glasnik Sumarskog fakulteta - Univerzitet u Beogradu (1987),
2015, Volume:
2015, Issue:
suppl.
Journal Article
Peer reviewed
Open access
This paper studies the applicability of DTM with the resolution of 4 ? 4 m
for the analysis of macro-topographic factors (terrain slope, aspect, terrain
ruggedness index) and one part of ...micro-topographic factors (occasional and
constant streams) as features important for vehicle mobility during timber
skidding. The analysis of directions of timber extraction in relation to the
spatial position of primary forest traffic infrastructure of the study area
was conducted in order to determine from which forest areas timber will be
extracted up or down the slope (moving of loaded vehicle). Determination of
water bodies (streams) and the surrounding sensitive areas was carried out
using GIS tool TauDEM. Unevenness of the terrain was determined based on the
Terrain Ruggedness Index (TRI) which showed moderately to very rugged terrain
on 60.1% of the research area where vehicle mobility could be difficult (if
not impossible) i.e. the necessity of a secondary forest road network is
clear. DTM analysis of study area regarding vehicle (skidder) mobility and
possible planning of timber extraction indicated different availability and
quality of data. Digital terrain models present a good basis for the analysis
of key constraints for forestry vehicles mobility or terrain trafficability
(slope and direction of timber extraction). Using DTM of higher resolution
(e.g. LiDAR images), will increase the accuracy of the results and the
quality of the analysis.
nema
Izvoženje drva forvarderima, obilježava kotrljanje drva na kotačima, prihvat i sakupljanje sortimentnom metodom izrađenoga drva hidrauličnom dizalicom, iz čega proizlazi i zahtjev za paralelnom ...mrežom sekundarnih šumskih prometnica međusobnoga razmaka dvostrukoga dosega dizalice.
Rad se bavi prikazom: 1) dimenzijskih i masenih značajki forvardera u svijetlu norme ISO 13860 (2016) te 2) plana raspodjele tereta forvardera kojega je razvio njemački Kuratorij za šumski rad i šumsku tehniku (KWF), s ciljem pomoći šumarskim stručnjacima pri nabavci, odnosno korištenju ovih šumskih vozila.
Za primjerni forvarder odabran je teški osmokotačni forvarder Komatsu 875, za koji su na osnovi mjerenja prikazane njegove dimenzijske i masene značajke, kao i plan raspodjele tereta s ciljem njegove ocjene.
Kritički osvrt je dan i na normu ISO 13860 (2016) s obzirom na neobuhvaćanje nekih dimenzijskih (duljina i visina prednjeg te stražnjeg prepusta forvardera, kutovi i polumjeri prohodnosti vozila) i masenih (položaj točke težišta) pokazatelja forvardera, a koje opisuju i/ili služe modeliranju njegove kretnosti pri izvoženju drva s obzirom na smjer i uzdužni nagib terena. Isto tako, norma izrijekom ne spominje niti jedan pokazatelj okolišne pogodnosti (npr. nominalni tlak na podlogu).
Timber forwarding is characterised by carrying timber clear of the ground and loading timber assortments by a hydraulic crane, which results in the requirement for a parallel network of secondary forest infrastructure network where the distance between trails equals to double span of the hydraulic crane.
The paper presents 1) dimensional and mass characteristics of forwarders considering ISO 13860 (2016) standard and 2) forwarder load distribution plan developed by the German Kuratorium für Wadarbeit und Forsttechnik (KWF) to assist forestry experts in the purchase and use of these forest vehicles.
The heavy eight-wheel forwarder Komatsu 875 was selected as an example. Its dimensional and mass characteristics are shown based on measurements and the load distribution plan, aiming to evaluate the vehicle.
A critical comment is also given regarding the ISO 13860 (2016) standard due to the lack of some dimensional (length and height of the front and rear overhangs of forwarders, approach and departure angles and clearance radii) and mass (position of the centre of gravity point) of forwarders. These characteristics describe and serve to model its mobility during timber forwarding concerning the direction and longitudinal slope of the terrain. In addition, the ISO 13860 (2016) standard does not explicitly mention any indicator of environmental suitability (e.g. nominal ground pressure).
Na osnovi poznavanja dimenzijskih i masenih značajki forvardera, razvijen je model raspodjele osovinskih opterećenja te procjene kretnosti forvardera pri izvoženju drva uz i niz nagib terena. Model ...je zasnovan na poznavanju položaja točke težišta forvardera, deklariranoj nosivosti forvardera i duljini utovarene oblovine, graničnom nagibu kretnosti forvardera temeljem vučne značajke vozila pri izvoženju drva uz nagib terena te graničnom nagibu terena pri izvoženju drva niz nagib, kod kojega obodna sila poprima vrijednost nula, uz poštivanje ograničenja proisteklih iz prethodnih istraživanja.Simulacijsko modeliranje procjene kretnosti pri izvoženju drva uz i niz nagib terena prikazano je na primjeru osmokotačnoga forvardera Komatsu 875, deklarirane nosivosti 16.000 kg, opremljenoga pneumaticima 710/45-26.5 za koji je metodom podizanja osovine određen položaj točke težišta. Rezultati raspodjele adhezijskog opterećenja prednje i stražnje osovine forvardera ukazali su da pri izvoženju drva tvrdih listača mase 16.000 kg te duljine 4,82 m, uz i niz nagib terena u granicama ±70 % ne dolazi do prekoračenja zbroja dopuštenih opterećenja guma kotača po osovinama te dopuštenog opterećenja prednje i stražnje bogi osovine. Pri izvoženju drva uz nagib terena, do rasterećenja prednje bogi osovine dolazi kod nagiba terena >68 %. Za navedeni raspon uzdužnih nagiba terena, najmanji konusni indeks od 950 kPa za primjerni forvarder predstavlja mjeru okolišne pogodnosti, a izračunat je na osnovi nominalnog tlaka na podlogu referentnih (opterećenijih) kotača stražnje bogi osovine vozila.Granični nagib kretnosti nominalno natovarenoga forvardera uz nagib terena značajno ovisi o nosivosti šumskog tla iskazanoga konusnim indeksom, ali i o klizanju kotača vozila. Za iste vrijednosti konusnoga indeksa tla, pri vrijednostima klizanja kotača (10 – 15 %) koje odgovaraju najvećoj vučnoj korisnosti, granični nagib kretnosti forvardera ima niže vrijednosti, u odnosu na klizanje kotača (20 – 25 %) koje odgovara okolišnom ograničenju, odnosno početku erozionih procesa na nagnutim terenima.Granični nagib terena pri izvoženju drva forvarderom niz nagib terena kod kojeg obodna sila poprima vrijednost nula, značajno ovisi samo o nosivosti šumskog tla te se nije pokazao kao dobar pokazatelj ograničenja izvoženja drva. Određivanje ograničenja kretnosti forvardera pri izvoženju drva niz nagib terena u budućnosti će predstavljati istraživački izazov.
In the example of an eight-wheeled forwarder, a simulation model is presented for assessing the mobility of the forwarder when transporting timber uphill and downhill. The presented model shows the changes in forces during timber forwarding by a nominally loaded forwarder due to a wide range of changes in influencing factors: 1) the slope of the terrain, 2) the direction of timber forwarding, and 3) the soil bearing capacity expressed by the cone index. By incorporating the criteria/limitations of timber forwarding derived from previous research, the forwarder mobility model gains practical meaning; that is, the theoretical approach brings the reality of timber forwarding closer. The mobility model shown is based on easily measurable or available data but also on the position of the centre of gravity, which is relatively easy to determine by the shown method of lifting the forwarders’ axle with the use of portable scales and is usually unavailable to read in the manufacturers’ catalogue. All known criteria/restrictions of mobility of forest vehicles are primarily related to their movement uphill. The limitation of the skidder’s mobility when skidding timber downhill has been firmly determined, while there are no limitations in the literature for forwarding timber downhill. Gradeability of a nominally loaded forwarder downhill, where the thrust force takes the value of zero, did not prove to be a good indicator or a limitation of timber forwarding. Determining the mobility limitations of the forwarder during timber forwarding downhill will be a research challenge in the future.
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