ANALYSIS OF FOREST STANDS DAMAGES CAUSED BY THE USAGE OF HARVESTER TECHNOLOGIES IN MOUNTAIN AREAS

Jiří Dvořák
Department of Forest Harvesting, Czech University of Agriculture in Prague, Czech Republic

ABSTRACT

Mainly due to ecological and economical reasons more and more advanced technologies for logging and hauling are constantly in use. These technologies can also operate in regions with environmentally sensitive forest management. The area of the Ore Mts. is an example, because during its history it was exposed to severe stress caused by pollution by the regional industry. Impacts of the up-to-date logging systems on the forests during pre-commercial thinning were analyzed in this region (Harvester Timberjack 1070 and Forwarder Timberjack 810B). The results of the research showed, that the new harvester technologies must be the technologies of choice. The percentage of injured trees in individual age classes ranged from 1.50 to 2.38 %.

Key words: harvester technology, stand damages.

INTRODUCTION

The production costs of logging and hauling activities are constantly growing. To lower these costs, which is a top priority, new technologies are demanded or the ones in use are modified. Cost decreasing is considered by most foresters to be the main task. But most of them do not realise that the injuries of trees caused by logging and hauling operations mean a much more expensive problem in future than the present decrease of costs. Due to these injuries trees are threatened by fungous infections. The extent of this threat depends on the size and position of the injuries as well as on the tree species. The injuries also negatively affect the increment of certain trees.

Injuries create the risk of infection by wood-destroying fungi. Putrefaction of living, standing trees are concomitant circumstances of logging and hauling in forest stands [4] - the wood quality of such trees declines. Mainly trees with damaged roots and buttresses are infected by these fungi [2]. Through the roots the fungous infection spreads slower than through the buttresses, probably due to differences in the wood anatomy [4]. Differences can also be found between buttresses and the trunk. Whereas the infection of the lower parts of the tree spreads only in one direction, the infection originating from the trunk spreads into two directions. In the latter case the damage of the valuable trunk section is nearly twice as high during the same time interval.

The injuries of trees should be minimised, because measures such as sanitation are not very effective due to a very similar tissue structure and physiological functions of the fungous parasite and the wood. Chemical substances therefore destroy not only the fungus but also the treated tree [1]. The biggest and most dangerous tree injuries occur in the butt section, up to 60 cm in height, of tree species with thin bark (spruce) during skidding [8]. Additionally the anatomy of roots increases the danger of infection with Stereum sanguinolentum.

The increment of such infected trees declines and therefore they become removed out of the production process. Thereby not only the wood production function of the forest declines but also its other roles suffer [2]. Mainly spruce stands suffer from decay and damaging [4] - the biggest danger appears in homogenous, extensive forests with bad access. This is true for the region of the Ore Mountains, where this research was realised.

GOAL

The main objective was to analyse the damages caused by use of the harvester technology, Timberjack 1070 and Timberjack 810B forwarder (see parameters in Table 1) in the Kraslice forest management unit. This study was carried out within the research project "Renewal of the ecosystem of the Ore Mountains". The results of the analysis show the extent of the tree damages in stands where this technology is used. During collecting the data the age class of the trees, the injured tree section, and the reasons of the injuries, such as felling, handling the felled trees, storing the timber assortments onto skidding lines, their loading, and last but not least, the influence of other forestry mechanisation which is used in the area of logging and hauling activities, were taken into consideration. Important, and also taken into consideration, was the number of injuries of different sizes.

It was intended to show that the damage rate caused by harvester technologies is not too high. The use of these technologies in logging is increasing along with the tendency to reduce production costs, especially the costs of wages. The long developing trend of harvester technologies, as it was shown by independent researches, could, when properly used, decrease the impact on the forest ecosystem; it means no exposure to wood-destroying fungi and therefore no destabilisation of growths due to these fungi. Thus the damages are kept at minimum, the number of trees affected by decay is kept at minimum, and the quality of wood is not lowered.

METHODS

A mathematical-statistical analysis was used to assess the damages in the whole area investigated. It can be assumed that the highest rate of damages can be found directly on the skidding lines where the machines (harvester and forwarder) move. Therefore the damages were recorded and measured alongside the whole lengths of the skidding lines. But also all other damages in the operating area were recorded at the same time. All tree injuries were divided by tree sections (roots, buttress, stem), as well as by size intervals: 0 - 10 cm², 11 - 50 cm², 51 - 200 cm², 201 - 500 cm², and 501 - 1000 cm². A registration of other natural, technical and technological conditions and factors for detailed analyses based on the number code elaborated in the co-operation with the MZLU in Brno was an integral part of the realised experimental examination [3].

RESULTS AND DISCUSSION

The results presented in this paper can be divided into two groups:

1. The number of injuries according to the affected tree sections (root, buttress, trunk), and according to size intervals (in cm²).

2. The number of injured trees (Tables 2, 3, and 4).

A survey of injuries after harvester´s work was carried out for the age classes 3, 4 and 5. Even though it was not possible to verify a zero hypothesis for a single age class (Table 5), due to an insufficient number of measurements (44 stands), some differences were found. Harvester technologies using Timberjack 1070 and Timberjack 810B injured in a single age class from 1.50% to 2.38% of the trees left in the stands (Fig. 1). In age class 3 1.50% of the trees left in the stand were damaged, i.e. 19.3 trees/ha. In age class 4 the percentage of injured trees increased by 0.83 % up to 2.38% (23.7 trees/ha) and in age class 5 to 2.25% (13.0 trees/ha). The lowest percentage of injured trees in age class 3 was due to not too well developed buttresses. The buttresses of trees in age class 4 were more often injured by machines travelling along the skidding lines, by ground skidding, or by wrong piling of logs against or between trees on skidding lines. Trees were injured by a hydraulic jib of a forwarder. In the case of age class 3 trunks of trees were less often injured thanks to protection provided by branches situated lower on the trunk. The extent of injuries in age class 5 decreased as compared with that of age class 4 due to a greater spacing of trees and a thicker bark.

The total number of injuries was higher than the number of injured trees. The ratio between the number of injured trees and the total number of injuries amounted to 75.6%, 81.0% and 85.4% in age classes 3, 4 and 5 respectively. This was because there were two or more injuries per tree (Fig. 2). The number of injuries per tree increased with increase of stand density. The risk of decay rises with the number of injuries which leads to secondary commercial losses. The injuries were recorded in accordance to their distribution in respective tree sections:

• root up to a distance of 1 m from the tree,

• buttress,

• trunk, regardless of the injury position.

It is not possible to specify the tree sections with specific units because their metrical span is changing within age, natural conditions and the species. Therefore the damage was assessed specifically for each injured tree.

The injuries in tree sections can not be regarded from a quantitative point of view. There exist a different risk of fungous infection followed by spreading of decay throughout a tree, depending on the place of injury (root, buttress or stem).

Considerable differences between respective tree sections in respect of the number of injuries are evident in Fig. 3. These differences were approved by the scattering analysis - the hypothesis of mean value equality was generated with high reliability (Table 6). A detailed assessment of the differences between the sections was proved by Scheffe´s method for multiple comparing (Table 7). Differences between the roots and buttresses, and between the trunks and buttresses were statistically confident (at the confidence level 0.05). On the contrary, no significant difference was found between the roots and trunks.

Without taking the age classes into consideration, the root buttresses were damaged to the highest degree (18.9 injuries/ha). The damages of the root system amounted to 9.0 injuries/ha. The lowest number of injuries was found on the trunks - they amounted to 5.8 injuries/ha. The number of trunk injuries may be limited by the minimization of the interaction between a machine and a tree. This goal is reached when width of the skidding lines is between 3.5 and 4 m [7] and there are few obstacles on the skidding line. Obstacles increase the risk of skewing the machine and damaging the trunk by uprights, cabs or other components. Another danger for the trunk injury is a non-guided way of downfall in the case of lack of operator´s experiences or by cutting the overgrown trees, which can not be transferred by a logging head.

The last analysis concerned five intervals specifying the area of injury: 0 -10 cm², 11 - 50 cm², 51 - 200 cm², 201 - 500 cm², and 501 - 1000 cm². The hypothesis of equality of mean values of the number of injuries in individual intervals (Table 8) was verified. Then the differences between all interval pairs were assessed with the Scheffe´s method for multiple comparing (Table 9) at the significance level 0.05.

In the case of the root sections the smallest number of injuries occurred in the interval group 501 - 1000 cm², 0 - 10 cm², 201 - 500 cm², and 11 - 50 cm². The differences between these intervals were statistically indistinguishable (they formed a so called homogenous group). While the injury rate in the interval 51-200 cm² was significantly higher than in the remaining intervals.

In the case of the buttress sections the smallest number of injuries occurred in the interval group 0 - 10 cm² and 11 - 50 cm², and the greatest number in the interval group 201 - 500 cm² and 51 - 200 cm².

In the case of the trunk sections the smallest number of injuries occurred in the interval group 201 -500 cm², 501 - 1000 cm², 0 - 10 cm² and 11 - 50 cm², and the greatest in the interval 51 - 200 cm².

The injury ratio for respective tree sections is shown in Fig. 3. The smallest injuries (up to 10 cm²) were the least frequent ones. Their number amounted to 1.4 /ha. The injuries of this size occurring on trees with thicker bark did not affect the wood fibre and were not regarded as injuries. The number of injuries 11-50 cm² in size was 6.0/ha (regardless of age class). The highest number, i.e. 14.2 injuries/ha occurred in the case of injuries 51-200 cm² in size. In this case the number of injuries was significantly higher, and the probability of fungal infection and decay was very high. The numbers of injuries for the size intervals 201-500 cm² and 501-1000 cm² were 7.9/ha and 4.3/ha respectively. The injuries in these two intervals may have been caused by an intensive overdrive over the same buttress or root not protected by slash.

The injuries of these sizes are not exceptional neither at the exits from the analysed areas nor on the truck landing border. Injuries in these places are mainly due to a hydraulic jib or to handling with cut-outs.

CONCLUSIONS

There exists a series of logging and hauling technologies and their modifications for operational cutting. But none of them can be regarded as a perfect one that causes no damages in the forest stands. Not always we can choose technologies which cause the least amount of damage because they may not be used under concrete conditions because of very high production costs or a deficient technical background (vehicle fleet etc.) In spite of that there is a future perspective for the harvester technologies since this assortment method causes less damage than trunk methods, e.g. MP, horse, LKT injure 22 % of trees [8].

An analysis of possible technologies with goal-directed optimised logging and technological parameters or optimised technical parameters can be of remarkable significance in limiting the damages.

Reaching a minimum of damages in forest stands during the production process does not consist only in selection of the machinery and logging technologies but it is also necessary to follow the fundamentals related to engaging the TDS in the production process, i.e.:

• consistent structuring of stands,

• marking the trees for cutting

• observance of production techniques.

The economical production often does not match with the ecological point of view. But it must be realised that direct decontamination labour costs as well as future losses due to fungous infections decrease with increased use of new harvester technologies.

REFERENCES

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3. Dvořák, J., 2004: Rozsahy škod v lesních porostech způsobené nasazením těžebně dopravních strojů a návrh souvisejících těžebních opatření, [Extent of Damage in the Stands and Draft of Related Logging Measures], ČZU v Praze, 209 s., [in Czech].

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