UTILIZATION OF THE MHT-182HVT MOUNTAIN HARVESTER AND ITS EFFECT ON THE FOREST SOIL AND STAND

Łukasz Duszyński, Józef Walczyk
Department of Forest Works Mechanization, Agricultural University of Cracow, Poland

ABSTRACT

The results of a study on damage of forest soil and trees during timber harvesting works using the MHT-182HVT harvester are presented. Synthetic indexes of forest tree and soil damages were determined. A synthetic damage index for trees remaining in the forest after the harvesting operation reached the value of 8.14%. A special attention was paid to deep wounds damaging the wood tissue. However, trees with this type of injuries constituted only 2.26% of the total number of trees remaining in the harvested area. A synthetic forest soil damage index was 2.85%. Also the change of the soil compaction index in the harvester working area was determined. The compaction was determined in two variants. In the first variant the machine was moving along a skidding road covered with tree debranching residuals (branches and tree tops), and in the second variant no such a cover was present. In both cases the results were compared with soil compaction measured in the control plot.

Key words: harvester, soil compaction, tree damage, timber harvesting technology.

INTRODUCTION

Forests cover 47.2% of the total area of the Republic of Austria, and this index is among the highest in Europe. The total forested area in this country is 3.96 million ha with Norway spruce (Picea abies) as the main forest tree species covering 53.7% of this area (1 810 thousand ha). Other important forest tree species include common beech (Fagus sylvatica) covering 9.6% of the forested area (323 thousand ha) and Scots pine (Pinus sylvestris) covering 4.9% of the forested area (166 thousand ha). In Austria, similarly as in southern Poland, coniferous monocultures constitute the majority of its forested area (62.2%). These stands grow at high altitudes and belong to protected semi-natural forests. The annual wood increment is about 31 million m³, and is harvested in about 60%. Therefore, the growing stock of Austrian forests is constantly increasing, and at the present moment it reached 1 094 730 thousand m³. Saw-mill, pulp and paper, and other wood processing industries are of a great importance to Austrian economy. Almost 70% of saw timber, particle boards, and cardboard are exported to other countries of the European Union. Small private forests, up to 200 ha in area, constitute 53.8% of the forested area, while 14.9% is owned by the Austrian Federal Forests SA. The remaining forests belong to larger private owners or to political communities (31.3% in total) [1].

In Poland we have no experience in utilization of harvesters in mountain areas. However, due to frequent natural calamities, difficult work conditions, and labor force shortage this technology must be used. The utilization of a harvester not only permits to increase the efficiency of harvesting operations, shortens the period of time necessary for tidying the calamity area, makes work easier and safer, but also permits to give up a manual wood registration by foresters [3] which makes this process quicker. In Austria harvesters are adapted to work in mountain regions, and there is a considerable experience in Austrian forestry in this respect [15].

STUDY AIM AND OBJECT

The objective of studies conducted by the Department of Forest Works Mechanization, Agricultural University of Cracow was to determine technical and technological parameters of a Neuson-Ecotec MHT-182HVT type harvester and its influence on forest environment [2,3,12,17,18,19]. The present study was carried out in the Austrian mountain forest thanks to courtesy of Mr. Gerhard Bartl, a representative of the Neuson-Ecotec GmbH firm. A harvester of a MHT-182HVT type was the object of this study. It was equipped with a caterpillar driving system [8].

Harvester's technical data:

Thanks to a high torque it is possible to reach a high efficiency at low noise and small fuel consumption. This harvester is equipped with two independent hydraulic systems. One of them is responsible for machine movement constituting its driving system. It also permits to level the cabin and to fully turn it together with the crane. This system is provided with a double hydraulic pump system of a variable delivery which may reach maximum of 2x144 l min^-1 at working pressure of 300 bar. The second independent hydraulic system is responsible for supply of a proper amount of energy for work of the harvester's head. The delivery of the harvester's hydraulic system pump is 280 l min^-1, working pressure is 330 bar, and the hydraulic system capacity is 220 liters. In this system a pump of variable capacity with regulation of pressure and delivery (P/Q control) is used. The machine was equipped with a parallel rotational crane of a CH 175 type.

The harvester used in this study may move with the maximum speed of 3.1 km h^-1. Its driving system consists of two steel caterpillars 600 mm broad and 4045 mm long. The caterpillars have cleats 50 mm high and 10 mm broad, 190 mm apart. The machine pressure per unit area is 0.42 kg cm^-2. The harvester may work on slopes up to 25⁰ to the front and up to 15⁰ to each side. According to catalogue data the harvester may overcome upgrades up to 30⁰ (58%).

The harvester's cabin large lexan windows secure a very good view of the working area. The cabin is equipped with the TCM (Total Machine Control) systems securing easy operation. It also has air conditioning. The arrangement of indicators and controls is clear and systematized.

The harvester was provided with the Woody 6000 head of the following parameters:

MATERIAL AND METHODS

A study was conducted in a private forest located in Mönischkirchen (Styria, Austria). It was almost a pure Norway spruce stand of the following species composition: Norway spruce (Picea abies) 92%, Scots pine (Pinus sylvestris) 3%, silver fir (Abies alba) 2%, European larch (Larix decidua) 2%, and common beech (Fagus sylvatica) about 1%. There were also sporadically occurring individuals of other broadleaf tree species. The study area of 4.80 ha was situated on a slope up to 18⁰ in some places. The investigations were conducted in September when air temperature was about 10⁰C, wind velocity did not exceed 2 m s^-1, and soil moisture was about 21%.

In this 60-year-old stand the operation carried out during this study was the first treatment in its history. There had been no felling cycle followed in this forest. Initially there were about 1300 trees per hectare on the average, and after the treatment about 750 trees per hectare remained in the stand. The forest site type was determined on the basis of indicator plant species, and the site index class on the basis of the diameter breast high (D.B.H.) of individual tree species.

The study area was situated at about 850 m above the sea level on a slope of southeastern exposure descending to the valley bottom (water-course). This 60-year-old stand represented site index class II as determined on the basis of Norway spruce D.B.H. The site index class was also determined for silver fir and Scots pine (it was class II in both cases). In the forest floor vegetation the following species typical for the Fresh mixed mountain forest site type [10] were found: Luzula luzuloides (L. nemorosa), Rubus plicatus, Rubus idaeus, Carex sylvatica, Athyrium filix-femina, Mycelis muralis, Oxalis acetosella, and Senecio fuchsii.

The study area was located between two contour line forest roads but there were no skidding roads prior to the study. The skidding roads constructed during the operation were 3 m wide and 20 m apart. Their total length was about 400 m. The spacing of skidding roads was adjusted to the crane’s reach. These roads were cut out as the logging operation proceeded. The removal of trees from each skidding road was initiated at the lower contour line road and this process proceeded up the slope.

Branches left after the tree debranching process as well as cut off tree tops were deposited on newly created skidding roads. Thanks to this branch cover (45–65 cm thick on the average) the harvester's caterpillars were not in a direct contact with forest soil which was not damaged during the work. Placing logging residuals on skidding roads also prevented soil erosion. Driving over the branches accelerated the process of their mineralization.

a)

b)

The following three kinds of assortments were harvested:

a. Construction poles (thinner end diameter: 0.11–0.18 m) of four different lengths:

3.10 – 3.16 m ± 2 cm,
4.10 – 4.16 m ± 2 cm,
5.10 – 5.16 m ± 2 cm,
6.10 – 6.16 m ± 2 cm.

b.  Logs (thinner end diameter: ≥ o.19 m) of two different lengths:

5.10 – 5.16 m ± 2 cm,
6.10 – 6.16 m ± 2 cm.

c. Pulpwood (thinner end diameter: 0.06–0.11 m).

The other wood material was cut and thrown under harvester's caterpillars on a skidding road.

The soil compaction was measured using a cone penetrometer with a strain gauge. Each time 100 measurement replications were made with the penetration determination error up to 1 mm. The photo-optical measurement of the penetration value was registered in the counter channel of the APEK AL 154 interface [11]. The soil compaction was measured in a track created during harvester’s passage along a skidding road with and without branch cover as well as in the control area.

When the relationships between the harvester's driving system and the soil were investigated a special attention was paid to values of unit pressures exerted upon the forest soil. Hitherto, no allowable unit pressures exerted by machines upon the forest soil have been standardized. According to German publications [4] the allowable unit pressure of skidders should range from 89 to 275 kPa, while that of forwarders and working machines from 45 to 78 kPa, depending on soil properties. Russian scientists concluded that the allowable unit pressures for caterpillar vehicles may reach as much as 70 kPa, and for wheeled vehicles 150 kPa [5]. Wästerlund [7] as well as Matthies and Kremer [7] are of the opinion that the limit of the allowable pressure upon soil is 50 kPa. While Rónay [9] concluded that at pressures 50–120 kPa important changes take place in the soil structure.

While estimating the effect of machines on the stand a special attention was paid not only to the proportion of injured trees remaining in the stand after the treatment but also to the nature of wounds. Low situated wounds, susceptible to infection by rot fungi, are especially dangerous. Also the wound area is a very significant factor affecting the depreciation of the wood material. Usually wounds above 100 cm² in area covering 1/8 of the stem's circumference are considered to be the large ones.

Suwała [14] proposed to take the index of synthetic estimation of tree damage into consideration while estimating the effect of technological processes on the damage magnitude:

(1)

D₀ – total percentage of damaged trees,
D_0.1 – percentage of trees with at least one low wound (occurring at height ≤ 0.1 m),
D₁₀₀ – percentage of trees with the total wound area > 100 cm²,
D_0.125 – percentage of trees with at least one wound covering > 0.125 (1/8) of a circumference in the place of injury,
D_d – percentage of trees with a wood tissue wound.

All partial indexes in this formula represent the percentages of trees with respective damage characteristics in relation to the total number of trees remaining in the stand after the treatment. It is possible that a given tree with one or more wounds was used in calculation of the mean more than once.

The damages consisted of stem injuries, broken living branches, and root injuries noticeable within the root collar. The formula presented above shows that the lower is the value of the U_D index the smaller is the tree damage.

Considering the height above the ground the wounds were divided into three groups:

a.       low wounds (≤ 0.1 m),
b.       wounds at medium height (0.1–4.1 m) – the quality of this part of the stem greatly determines the quality class of a log,
c.       high wounds (> 4.1 m).

The group of trees with low wounds, situated at height up to 10 cm, also included trees with wounds not causing a direct danger of blue stain or fungal infection, e.g. bark abrasions without damage of the wood tissue.

Considering the wound area wounds were divided into two groups:

a.       wounds with area ≤ 100 cm²,
b.       wounds with area > 100 cm².

The wound depth is an important parameter determining the degree of tree damage (bark abrasion versus wood injury).

A stress state in the soil caused by vehicles in motion has been discussed by scientists since a long time. The description of soil vertical and horizontal strains is an important problem. It has been proved that there is a relationship between the soil vertical strain and the normal drive wheel load as well as its drive system. Also the effect of the torque is a source of horizontal and vertical strains. In order to fully describe traction characteristics of the transmission, besides description of the drive wheel – ground relationship, the description of drive forces and slips, as well as the determination of the area of the tire – ground contact and of the resistance forces, are necessary. The knowledge of the traction characteristics on a given soil makes the optimal utilization of the forest vehicle towing power possible. While the knowledge of limiting loads for a given soil permits to limit the excessive strain of the medium which is the cause of deep ruts and soil erosion [2,11].

However, it should be remembered that the movement of a vehicle over a strain susceptible ground is always accompanied by horizontal and vertical strains. The forces tangential (parallel) to the drive wheel are a source of the horizontal strain (in a horizontal plain), while the forces perpendicular (in a vertical plane) affect the vertical strain.

Suwała [14] proposed, similarly as in the case of tree damage, the calculation of the soil damage index including all disturbances and changes in the soil surface layer, and indirectly also injuries and damages of tree roots. The synthetic index of the soil surface layer damages is expressed by the following formula:

(2)

where:

G_ko – percentage of volume of ruts (or its increase during successive passages) in the soil layer 0.1 m thick,
G_kp – percentage of volume of hoof-prints in the soil layer 0.1 m thick,
G_bp – percentage of volume of shallow furrows (mainly soil packing) of the mean depth up to 0.05 m in the soil layer 0.1 m thick,
G_bg – percentage of volume of deep furrows (largely made by skidded logs) of the mean depth above 0.05 m in the soil layer 0.1 m thick.

Taking into account the technological process during which the harvester moves only along skidding roads covered with residuals the above formula assumes the following form:

(3)

The volume of the soil surface layer 0.1 m thick was assumed to be the soil damage reference level because in coniferous stands 70–90% of the main tree roots are located there. The percentage of deep wounds was given a double rank. The lower is the index the smaller is the percentage of volume of the soil surface layer structure disturbance, and at the same time the smaller is the extent of the forest floor vegetation damage.

To determine the synthetic index of tree and soil damage the following relationship was used:

(4)

RESULTS AND THEIR ANALYSIS

The change of the soil compaction caused by the harvester's movement on a skidding road is graphically shown in Fig. 4.

Unit pressures generated by the harvester were low amounting to 44.4 kPa. The greatest increase of soil compaction was found for the 0.035 – 0.105 m depth range in the case of the harvester's passage over a skidding road without a branch cover (Fig. 4).Thanks to branches placed on a skidding road the increase of soil compaction was limited over twice. The difference in soil compaction between the control plot and a skidding road covered with branches varied from 0.89 to about 1.00 MPa for the depth of 0.07 m reaching here the greatest value. However, the increment of compaction was only 11% in this case. At a 0.09 m depth this increment decreased to 8.37% (from 1.11 to 1.21 MPa). At depth greater than 0.105 m a decline of the influence of the harvester's passages on soil compaction was observed.

In the case of the harvester's movement on the uncovered skidding road the soil compaction increment reached the maximum value of 26%, from 0.89 to 1.12 MPa for a 0.09 m depth. At a 0.14 m depth the compaction increment was only 6%. Beginning with a 0.2 m depth changes in soil compaction were small varying from 0.39% to 5.25% in relation to the control plot. These changes could have been caused by the soil structure variation and not by the harvester's passage.

In Fig. 5, besides the synthetic tree damage index (U_D), wood tissue damage index (D_d), and the index for trees with low wounds (D₀₁), also the index of wood damages irrespective of their type and character is presented. This was due to the fact that this latter index is commonly used, and therefore its interpretation in the discussion is possible.

A very low value of the wood tissue damage index is particularly worth to be noticed. This is a satisfactory result because the wood tissue wounds make trees susceptible to fungal infection which in turn lowers the productive value of wood (blue stain).

It should be emphasized that no trees with the total damage area of over 100 cm², nor trees with damages above 1/8 of the stem's circumference, were found.

The synthetic tree damage index obtained by Suwała [13] in his study conducted in lowland Scots pine stands where late thinning was carried out using a harvester technology amounted to U_D = 7.8%. The index obtained during the study presented in this paper was U_D = 8.14% (Fig. 5), and it was only by 0.34% higher than that of Suwała. However, it should be taken into consideration that investigations of Suwała [14] were conducted in the forest where the felling cycle was followed from early clearings to early thinning. Moreover, his investigations were conducted in a lowland area where difficulties associated with slopes were absent. While our study was conducted in a mountain area with slopes of 18⁰, and the late thinning carried out during this study was the first treatment in history of the investigated stand.

The synthetic tree damage index in respective diameter classes is presented in Fig. 6. The following four diameter classes were distinguished: D.B.H. ≥ 0.25 m, 0.19–0.24 m, 0.11–0.18 m, and ≤ 0.10 m. The index values varied from 3.93% for trees in class 0.19–0.24 m to 13.19% for trees in class ≤ 0.10 m.

The synthetic soil damage index.

In the graph presented above the synthetic soil damage index and its components are shown. The synthetic soil damage index itself is small. This resulted from the type of timber harvesting technology used. The harvester traveled only along the skidding road, and therefore, trees in the process of their felling and debranching constituted the factor which caused these small damages. These trees only for a short period of time could have been in contact with the soil.

The synthetic soil surface layer damage index calculated by Suwała [13] in his study on timber harvesting during late thinning in lowland Scots pine stands using a harvester technology was U_G = 3.8%. Moreover, he concluded that in respect of the soil damage index (U_G) value, the distance of 20 m between newly constructed skidding roads was the optimal one. The increase of this distance to 40 m caused the increase of  the soil surface layer damage index to 4.7% (increase by about 24%), while at 60 m distance the value of this index was 5.5% (increase by about 45%).

The synthetic tree and soil damage indexes are presented in Fig. 8.

On the basis of the analysis of damages in the stand caused by timber harvesting operation it may be concluded that for the assortment method (short wood) at a distance between skidding roads of 20 m the influence of the technological process in form of the soil damage was small (2.85%), and in form of stand damage it was higher (8.14%). It should be remembered that in determination of the stand damage index all trees, also those with a single damage characteristic (e.g. broken living branches) were taken into consideration. During the treatment (the first one in history of the investigated stand) at high stocking and crown closure (about 1300 trees per hectare prior to the treatment) the synthetic tree and soil damage index was 5.49%. The available results of other authors [13,14] showed that the tree and soil damage index in stands with a full felling cycle varied from 2.8% (assortment method) to 6.9% (full-tree method).

CONCLUSIONS

1. The harvester moving along the skidding road covered with residuals of the debranching process affects the soil compaction to a 0.105 m depth, while in the case of an uncovered skidding road to a 0.14 m depth.

2. The spreading of debranching residuals over a skidding road along which the harvester is traveling decreases the influence of a machine upon the soil by nearly 70%.

3. The greatest soil compaction increment on an uncovered skidding road was small amounting 26%, while on a skidding road with a branch cover the compaction increased by only 11% at the most.

4. The technological timber harvesting process investigated during this study did not cause any significant damage of wood tissue of the trees remaining in the stand after the treatment. It was only 2.26%.

5. The synthetic tree damage index reached the lowest value in the case of trees 0.19–0.24 m in D.B.H. It was 3.93%.

6. The synthetic soil damage index reached a very low value of 2.85% in the case when the harvester was traveling along skidding roads covered with branches.

7. The synthetic tree and soil damage index was 5.49% which, considering the fact that this was the first treatment in history of the investigated stand, it was a very good result.

8. Unit pressures during this technological process of timber harvesting reached the value of only 44.4 kPa, and according to many cited authors this was an admissible value.

REFERENCES

1. Bernadzki E., 2006. Lasy i leśnictwo Unii Europejskiej [Forests and Forestry European Union]. Dyrekcja Generalna Lasów Państwowych. Warszawa [in Polish].

2. Dvořák J., Karnet P., Pavla Rusnáková P., 2008. Comparision between electronic acceptances recorded by harvester and measuring frame kesat in the conversion depot. EJPAU 11(4), #08, http://www.ejpau.media.pl/volume11/issue4/art-08.html.

3. Eisele E.L., 1987. Umweltfreundliche Forstmaschinen [Environment-friendly machines]. Allgemeine Forst Zeitschrift, 4 [in German].

4. Jermaliew W.P., Winogorow G.K., 1995. Mechanika wozdjejstwija maszin na lesnyje poczwy [Mechanics of the machines effect on forest soil]. Lesnoja Promyszlennost, nr 3 [in Ukrainian].

5. Kormanek M., Walczyk J., 2000. Oddziaływania kół ciągników zrywkowych na glebę leśną [Influence of wheels of skidding tractors on forest soil]. Inżynieria Rolnicza, 7,  77–84 [in Polish].

6. Matthies D., Kremer J., 1999. Bodenmechanische und Bodenphysikalische Ergebnisse im Rahmen des "Informationssystems zum bodenverträglichen Forstmaschineneinsatz" [Mechanics and physics of the forest soil within the framework of machines application information system]. FTI 5+6, 35–38 [in German].

7. Folders of firms Neuson-Ecotec  GmbH.

8. Rónay E., 2004. Svetové trendy motivujú k novému mysleniu [The word trends motivate to new thoughts]. Les 2004,  11–12 [in Slovak].

9. Sikorska E., 2006. Siedliska leśne cz. II Siedliska obszarów wyżynnych i górskich [Forest side part II Forest side upland and mountainous]. Zeszyty Naukowe Akademii Rolniczej w Krakowie [in Polish].

10. Słowiński K., 2007. Badania zwięzłości w szkółce leśnej na grzędach różnych gatunków drzew [The investigation of conciseness at forest school on perches of different the trees' species]. Prace Komisji Nauk Rolniczych. PAU, 9, 149–156 [in Polish].

11. Smulczk Ł., Tracz K., 2008. Metabolizm oddechowy gleb w różnych wariantach sposobu przygotowania gleby oraz udziału domieszek na zalesionych gruntach porolnych [The respiratory metabolism of soils in different variants of way of preparation soil as well as part admixtures on afforested soils the down-agricultural]. Sylwan  11, 63–71 [in Polish].

12. Suwała M., 2003. Uszkodzenia drzew i gleby przy pozyskaniu drewna w wybranych rębniach złożonych na terenach nizinnych [Folded trees and soil's damages near gain over in chosen wood forest cutting on lowland terrains]. Prace IBL 949 [in Polish].

13. Suwała M., 1999. Uszkodzenia drzew i gleby przy pozyskiwaniu drewna w późnych trzebieżach drzewostanów sosnowych [The trees and soil's damage near logging in late thinning of pine stands the wood]. Prace IBL nr 873 [in Polish].

14. Uhl E., Ohrner G., Matthies D., Kremer H., Wokf B., 2003. Einsatzempfehlungen fűr Rad- und Raupenfahrwerke [Indications concerning use of wheeled and tracked running gears]. LWF aktuell, Nr. 39, 11–14 [in German].

15. Walczyk J., Duszyński Ł., 2007. Uszkodzenia drzew i gleby przy prowadzeniu prac pozyskaniowych. Metodologia badań [The trees and soil's damage near leadership of logging works. Methodology of research]. SGGW Warszawa [in Polish].

16. Walczyk J., Kormanek M., Walczyk M., Koreň J., 2000. Oddziaływanie małego kołowego transportera MKT 6x6 na stan gleby podczas zrywki drewna [The influence the small circular transporter MKT 6x6 on state soil during skidding of wood]. Inżynieria Rolnicza, 6, 305–312 [in Polish].

17. Walczyk J., Kormanek M., Walczyková M., 2001. Oddziaływanie ciągnika Timberjack 240B na glebę podczas zrywki na zrębie [Influence tractor Timberjack 240B on soil during skidding on framework]. PAU, Prace Komisji Nauk Rolniczych, 3, 169–178 [in Polish].

18. Walczyková M., Walczyk J., Kormanek M., 2002. Determination of forest soil traction parameters. EJPAU 5(2), #6, http://www.ejpau.media.pl/volume5/issue2/forestry/art-06.html.

19. Wästerlund I., 1986. Effects of Damage on the Newly Thinned Stand due to Mechanized Forest Operations Manuskript. Univerzita požnohospodárskych vied, Upsala, Svédsko, 1–4.

Accepted for print: 18.05.2009

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