Comparison of damage to residual stand due to applying two different harvesting methods in the Hyrcanian forest of Iran: cut-to-length vs. tree length

[Research]

Comparison of damage to residual stand due to applying two different harvesting methods in the Hyrcanian forest of Iran: cut-to-length vs. tree length

R. MousaviMirkala

Department of Forestry, Faculty of Natural Resources, Urmia University, Urmia, Iran.

E-mail: rostammousavi@yahoo.com

(Received: June. 26. 2016 Accepted: Dec. 18. 2016)

INTRODUCTION

Nowadays, damage to residual stand is getting important due to increasing losing forest in many part of the world, therefore sustainable forest management become important. Defining and implementing sustainable forest management with aiming at low impact logging is one of the most critical challenges facing countries now. Forest managers are always under increasing pressure to meet the growing demands for all types of forest products and services, while need to consider environmental impact of their activities. The demands on the natural forests in Iran are numerous and increasing with demographic changes and changing land-use requirements. As a consequence of the increase in demand for forest products and services and the reduction of the forest resource base, concern has risen over whether the demands for forest products can be met in a sustainable manner.

Forest harvesting is always with damage to residual stand which can be direct to trees and indirect to future stand. Direct damage includes damage which is happened during harvesting and includes damage to the stem (scarring or removal of bark), crown (breaking), and root (exposed) (Mousavi Mirkala 2009). Damage to residual stand decreases potential of forest production. Indirect damage caused nutrition loses due to wood and branches removal, soil compaction, site condition changes, and other impacts which decreases potential of forest stand to present good and services to people (Nikooy 2007). In this research, direct damage is studied under comparing condition of the cut-to-length and tree length methods.

 In the cut-to-length method, trees are felled, delimbed and bucked to assortments in the stump area. In this method, roadside landings are minimal since all processing is done in the cutting area and high roadside piles can be made. The method also allows for better sorting and storage of various wood assortments. This method is the most common method in many countries (Mousavi Mirkala 2009). In the tree length method, trees are felled, delimbed and topped in the cutting area. Delimbing and topping may occur in the stump area or at a point before roadside. Trees are mainly skidded to roadside with cable or grapple skidders. The tree-length method is most applicable to clear cutting, and can be used in row thinning (Pulkki 1997). In the Caspian forest, logging operation is generally performed using selective cutting methods including single and group selection systems.

 In many developing countries, the main issues in harvesting were providing wood and material for wood industry without paying attention to the residual stand. In the last decades with increasing concern about losing forest due to overharvesting, scientists looking for a way to decrease negative effect of harvesting, therefore, FAO implemented code of practice in several developing countries such as South Africa, Malaysia and Indonesia (FAO 1998 a, b, c; FAO 2002 a, b, c) The extent of damage is highly related to the methods used. Ground-based skidding with skidder, which is used in primary transportation because of the low cost and high efficiency, highly influences the residual stand and forest soil (Najafi et al. 2004). For the post - harvesting assessment of a logging operation, getting an accurate measure of residual stand damage is important (Stephen & Craig 1997). An application for the residual stand damage study occurs when different harvesting systems are being compared for their ability to decrease damage to the residual stand (Stephen & Craig 1997). Damage to the residual stand is reduced significantly through the introduction of low impact logging in developing countries (FAO 1998 a, b, c; FAO 2002 a, b, c). Using techniques, such as pre-harvest inventory, pre-harvest planning of roads, skid trails and landings, as well as appropriate felling and processing techniques (directional felling) has led to a reduction in the level of damage to the residual stand (Hendrison 1990). Rotation lengths, cutting period, type of equipment used, operational plan, and operator skills influence the residual stand damage and also stand quality (Ostrofsky 2001).

Different studies about the damage to the residual stand have been conducted in Iran. For example, Rashidi (1995) studied mechanical damage to the residual stand in a Fagus orientalis stand in Emamzadeh Ebrahim, Guilan Province, Iran. Hosseini et al. (2000) analyzed the impact of two different timber extraction systems (cable and ground-based skidding systems) on the natural regeneration in two compartments of Hyrcanian forests in Northern Iran. The amount of damage to all stages of the regeneration was significantly higher in the skidding operation than in the cable system. Nikooy (2007) revealed that damage to the residual stand in conventional logging was 23.5 % higher than that of low impact logging. Mousavi Mirkala (2009), studied damage to residual stand due to applying two short-log and long-log methods under comparable condition in Hyrcanian forests. The results showed that damage to the residual stand in the long-log method was higher and heavier than in the short-log method. Also depth and severity of injuries were more considerable in the long-log method than those in the short-log method.

Globally there is a long history of research regarding damage to the residual stand which shows the importance of the issue. Westveld (1926) initially pointed out the significance of injury to coniferous reproduction due to logging operations. He studied the post - logging damage in all trees and seedlings with a diameter higher than 2.5 cm. Wales (1929) studied damage to residual stand due to skidding by tractor in the pine forests of Arizona, USA. He introduced guidelines, including 12 suggestions for driver and choker setter, in order to reduce damage caused by tractor skidder. Vasiliauskas (2001) compiled a comprehensive literature review of studies on damage to residual stand. Nikooy et al. (2010) considered the levels of the residual tree damage in selection-managed stands and observed that 25-35 % of the residual trees had been injured at some extent due to logging. Study about damage to residual stand continued by Badraghi (2013), Ezzati & Najafi (2010), Tavankar & Bonyad (2014) who reported various issues about it.

The present study was conducted to complete the previous study about damage to residual stand due to practicing the short-log and long-log method (Mousavi Mirkala 2009) as well as damage to regeneration. The aim of the study was to determine intensity, occurrence and severity of damage due to applying the tree length and cut-to-length methods.

MATERIAL AND METHODS

Stand description

The study was conducted in Nav watershed, Hyrcanian forests, Northern Iran. The study area was located between 31°53’ and 31°56’ N, and between 41°72’ and 41°65’ E (Fig. 1). On the basis of the meteorological observations and according to Köppen's classification (Kimmel 2001), the climate of the area is temperate; the mean annual temperature is 12.6°C. In general, the relative humidity is high; with the annual rain fall varying between 1000-2000 mm per year.

Fig. 1. Location of the study area.

Study sites

They study area was located on Kilesara district belongs to Nav watershed in Northern Iran. Study on damage to winching strips was concentrated on parcels 1410 and 1412 and

sparsely in the other parcels. Study areas are highlighted in the Fig. 1.

Total surface area of district are 1397 ha which is  covered by several broad-leaved tree species such as Oriental beech, Fagus orientalis;  hornbeam, Carpinus betulus; Caucasian alder, Alnus subcordata; Norway maple, Acer platanoides; Common lime, Tilia rubra; and European pear, Pyrus communis.

Table 1. General description of the study area.

                   *4800 m of skid trail is studied.

Data collection

Damage to the residual stand and regeneration along the winching strip was studied in sites randomly located within the working area.

The transect method was used to determine the percentage of damage and type of damage at log extraction stage along skid trails. Species, DBH and the tree growth stages including sapling (height  less than 1.3 m), small thicket (DBH < 2-4 cm), thicket (DBH > 4-10 cm), and larger trees were recorded along the winching strips and skid trails and then, each tree was examined for any kind of damage. All injured saplings and trees were measured, recorded and then classified according to three main classes of damage: 1) one wound per tree; 2) 2-3 wounds per tree; 3) more than 3 wounds per tree. In addition, total number, diameter and tree species around the skid trails  as well as  winching strips, total damaged trees, location of wound(s) on each tree (on roots, up to 1 m, above 1 m), size of wounds (less than 100 cm², between 100-1000 cm² and more than 1000 cm²) and degree of injuries (deep and light) were recorded.

The length of the skid trail and winching strips differed, but the width of them was kept constant at 6 m (3 m distance from centerline of winching strips or borderline of skid trails).Because of the different surface area of the winching

strips, the calculation of percentage damages was weighted as follows (Zobeiry 1994):

where M_w = average percentage of damaged trees along winching strip;

g = percentage of damage along winching strip in the sample;

s = surface area of winching strip in the sample, ha;

i = sample number;

n = number of samples.

A 2 × 3 factorial design were applied to elucidate the effects of harvesting method and the tree's growth stages on damage rates. Two–Way ANOVA and Tukey's HSD tests were applied for data analysis such as of Analysis of variance of damage to trees and regeneration in different harvesting methods. All analyses were performed using SPSS 18 statistical software package at the significance level of P ≤ 0.05. All results were reported as Mean ± SE. The t-tests were used to measure whether there is a significant differences between the mean percentage of damaged trees in the two methods.

RESULTS

Damages along winching strips

According to the cut-to-length method, in 67 of the winching strips, 102 out of 369 trees were wounded as a result of the winching operation, while based on the tree length method, in 71 winching strips, 86 out of 342 trees were wounded as a result of this operation. The percentage of damage to the residual stand in the cut-to-length and tree length methods were 36% and 27%, respectively. Table 2 shows a summary of collected data in winching strips. 139 winching strips (in favor direction) are studied in both methods. All trees and regenerations were recorded in the predefined area.

Table 2. Summary of collected data in winching strips.

Totally, 3 or more wounds per stem were found to be the least common, for both methods. Percentage of two wounds and 2-3 wounds per stem in the cut-to-length method were 9.7 % and 9.1 % less than those in the tree length method, respectively. The percentage of one wound per stem in the cut-to-length method was higher than that in the tree length method by 18.1 % (Fig. 2).

Fig. 2. Percentage of number of wounds in the damaged tree along winching strips in the tree length and cut-to-length methods.

Overall, in both methods, 17 % of the damage was located on the roots, 71 % was located up to a height of 1 m on the bole, while 13 % was located above 1 m.

In the cut-to-length method, the percentage of damage on root and up to 1 m was higher than in the tree length method by 2%. Adversely, the percentage of damage observed above 1m in

the cut-to-length method was found to be 4 % less than that found in the tree length method (Table 3). Both in the cut-to-length and in the tree length methods, in 39 % of the cases the surface area of the wounds were less than 100 cm², in 46.5 %  between 100-1000 cm², while in 14.5 %  more than 1000 cm². In the cut-to-length method, the percentage of wounds with a surface area less than 100 cm² was higher than in the tree length method by 4%, while the percentage of wounds with surface between 100-1000 cm² and more than 1000 cm² was less than in the tree length method by 1% and 3%, respectively.

Finally, the percentage of deep wounds in the cut-to-length method was higher than in the tree length method by 1 %. Fig. 3 shows the percentage of wound in a distance from winching strips. The most of damaged trees was located up to 1 m and the damaged trees decreased with increasing distance from winching strips.

Damage to regeneration along winching strips

Table 4 shows damage to regeneration at three stages inducing sapling, small thicket and thicket. The results showed that damage to regenerations in the tree length method was less than in the cut-to-length method. The number of stem from sapling stage to small thicket and thicket stage decreased 53 % and 68 % in both methods, respectively. Table 5 shows different types of damage to regeneration in winching strips. In all three classes, the highest damage was related to sapling, followed by small thicket and thicket.

Table 3. Summary of damage to trees in winching strips.

Fig. 3. Damage to trees in winching strips in distance from centerline in the tree length (a) and cut-to-length (b) methods.

Table 4. Percentage of damaged regeneration in winching strips.

Table 5. Different types of damage to regeneration in winching strips.

Damages along skid trails

Damage to the residual stand along the skid trails occurs during the construction of the trails, as well as during log skidding. The results obtained from the cut-to-length method showed that 248 out of 1065 trees and regenerations were injured as a result of the skidding operations (23.3 %). In the tree length method, of 239 out of 1056 trees and regenerations, were injured as a result of the skidding operations (22.5 %).

Overall (in both methods), 36.1 % of trees had 1 wound in the stem, 43 % had 2-3 wounds, while only 20.1 % had more than 3 wounds (Fig. 4). The number of one wound per stem in the cut-to-length method was higher than in the tree length method by 16.3% while the number of 1-2 wounds and more than 3 wounds per stem in the cut-to-length method was higher than those in the tree length method by 2.8% and 13.5 %, respectively.

Fig. 4. Number of wounds as percentage on the damaged tree along skid trails for the tree length and cut-to-length methods.

The number and percentage of damaged trees at various diameter classes at skid trails is shown in Table 6.

Table 7 shows a detailed data on damage to trees in the skid trail. Most of the recorded damage was deep and was located up to 1 m. The wound surface area was mostly 100-1000 m². In total, 21% of the trees’ wounds were located on the roots, 71.6 % on up to 1 m and 7.5 % on above 1m. The number of damage on the roots in the cut-to-length method was higher than in tree length method by 3.7 %. The numbers of damage on a height 1 m above the ground and higher than 1 m in the tree length method were higher than in the cut-to-length method by 2.4 % and 1.3 % respectively. Overall (in both methods), 27.6 % of the wounds had a

damaged area less than 100 cm², 49.8 % were between 100-1000 cm², and 23 % were more than 1000 cm². Percentage of wound area less than 100 cm² and between 100-1000 m ² in the tree length method was higher than in the cut-to-length method by 1.8 and 1.1 %, respectively. However, the number of wound area between 100-1000 cm² in the cut-to-length method was 4 % higher than in the tree length method. In the tree length method, the number of deep wounds was higher than in cut-to-length method by 2.2 %.

Fig. 5 shows the distribution of damaged tree in associated with distance. By increasing distance from border of skid trails, damage decreased. So, the most damaged trees (84 %) were located less than 1m away from border of skid trails or 3m from centerline of skid trails.

Fig. 5. Damage to trees around skid trail at different distance from borderline of skid trails in the tree length and cut-to-length methods.

Table 6. Number and percentage of damaged trees at various diameter classes in skid trail.

Table 7. Summary of damage to trees in skid trails.

Table 8 shows damage to regeneration along skid trails.

Similar to winching strips, the most damaged trees was related to sapling, followed by small thicket and thicket.

Two-Way ANOVA test revealed that neither interaction of harvesting method and the tree growth stages nor harvesting methods affect damage rate. However, the tree growth stages significantly affected the damage rate (Table 9 and Table 10).

Turkey’s HSD test depicted that sapling significantly differed from small thicket and thicket, showing the lowest damage rate (Fig. 6). In both methods, there were not significant differences on the number of tree damages between the winching strips (p-value = 0.76) and skid trails (p-value = 0.5).

Table 8. Different type of damage to regeneration in skid trails.

Table 9. Analysis of variance of damage to regeneration (winching strips) in different harvesting methods and tree growth stage.

The highest damage rate was recorded in the cut-to-length method as well as small thicket and thicket stages, while the lowest observed in the tree length method as well as sapling and small thicket stages (Fig. 7).

Fig. 6. Damage rate at different tree growth stages in winching strips. Different letters on columns depicted statistically significant differences.

Table 10. Analysis of variance of damage to regeneration (skid trails) in different harvesting methods and tree growth stage.

Fig. 7. Damage rate at different tree growth stages in skid trails. Different letters on columns depicted significant differences.