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

Document Type: Research Paper

Author

Urmia University

Abstract

Damage to residual stand is unavoidable and it is one of the main important issues in the forest harvesting. Trees damage may occur in felling and skidding work phase or during skid trail construction. In any case, damage can be very serious to residual stand. Detailed study is necessary to find out the amount and severity of damage to trees; therefore district 14 of Kilesara in Guilan Province, Iran was selected for the study. The cut-to-length and the tree - length methods are practiced in the Hyrcanian forest. Applying any of these two methods is mostly related to dimensions of woody material, technical characteristics of skid trail, and machinery availability. A residual stand which is left after practicing such a method, is damaged in different way which needs to be studied in detail. The length of the winching strips and skid trails 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). All trees and regenerations around winching strips and skid trails are investigated for finding any sign of damage or injuries. The results showed that along winching strips, the percentage of damage to the residual stand was 19.5 and 18 %, while the damages along skid trails reached 25.4 and 31 % in the tree length and cut-to-length methods, respectively. The results of this study suggest that damage to the residual stand is considerable and should be reduced in order to improve the quality of stand at future.

Keywords


[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)

ABSTRACT

Damage to residual stand is unavoidable and it is one of the main important issues in the forest harvesting. Trees damage may occur in felling and skidding work phase or during skid trail construction. In any case, damage can be very serious to residual stand. Detailed study is necessary to find out the amount and severity of damage to trees; therefore district 14 of Kilesara in Guilan Province, Iran was selected for the study. The cut-to-length and the tree - length methods are practiced in the Hyrcanian forest. Applying any of these two methods is mostly related to dimensions of woody material, technical characteristics of skid trail, and machinery availability. A residual stand which is left after practicing such a method, is damaged in different way which needs to be studied in detail. The length of the winching strips and skid trails 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). All trees and regenerations around winching strips and skid trails are investigated for finding any sign of damage or injuries. The results showed that along winching strips, the percentage of damage to the residual stand was 19.5 and 18 %, while the damages along skid trails reached 25.4 and 31 % in the tree length and cut-to-length methods, respectively. The results of this study suggest that damage to the residual stand is considerable and should be reduced in order to improve the quality of stand at future.

 

Key words: Damage to residual stand, Post harvesting assessment, Skid trail, Winching strip, Iran.


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.

Study area

Kilesara district 14

Silvicultural treatment

Elevation range (m)

Aspect

district size  (ha)

Slope (avg.)

Regeneration condition

Soil pH

Gross volume (m3.ha-1)

Crown cover

Specie (volume precentage)

Avg. skid trail length *

Avg. winching strip length

Single tree selection method

700 (200-1600)

Noth, North East, North West

54

0-30 % (11%), 30-60 % (38%), 60-80% (28%), 80-100% (14%), > 100% (9%)

Medium to good

4.8-5.7

249.58

> 70 % (37.7), 40-70% (28.3), < 40% (34%)

F. oreintalis (44%), C. betulus (22%), A. subcordata (5%), others species (29 %)

750 m

33 m

                   *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):

       [i=1, 2,… n]      

 

 

where Mw = 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.

Method

Number

of winching strip

Sum

of strip length (m)

Sum of area (ha)

Number of trees in all strips

Number of regeneration

Sapling

Small thicket

Thicket

Tree length

71

2060

1.24

342

599

280

187

Cut-to-length

67

2166

1.30

369

653

293

191

 

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.

 

 

 

Tree length method

Wound place

On root

Up to 1 m

14 (16%)

60 (70%)

>1 m

12 (14%)

Wounds area

<100

33 (37%)

100-1000

40 (47%)

>1000

13 (16%)

Degree of  wounds

Deep

71 (82%)

Light

15 (18%)

 

 

 

Cut– to-length method

Place of wounds

On root

18 (18%)

Up to 1 m

73 (72%)

>1 m

11 (10%)

Wounds area

<100

42 (41%)

100-1000

47 (46%)

>1000

13 (13%)

Degree of  wounds

Deep

70 (81%)

Light

32 (19%)

 

 

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.

Harvesting method

Tree length method

Cut-to-length method

Regeneration stages

Number in strips

Sapling

Small thicket

Thicket

Sapling

Small thicket

Thicket

599

280

187

635

293

191

Number of damaged

76

58

40

102

70

53

Percentage of damage

12.7

20

21

15.6

23.1

27.7

 

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

 

 

 

 

Tree length method

 

Leaned

Sapling

40 (65.6%)

Small thicket

18 (29.5%)

Thicket

3(4.9 %)

 

Wounded

Sapling

38 (43%)

Small thicket

27 (30%)

Thicket

24 (27 %)

 

Roots off the ground

Sapling

27 (51%)

Small thicket

13 (24.5 %)

Thicket

13 (24.5 %)

 

 

 

Cut-to-length method

 

Leaned

Sapling

33 (55 %)

Small thicket

22 (36.7%)

Thicket

5 (8.3%)

 

Wounded

Sapling

28 (32.9 %)

Small thicket

25 (29.4%)

Thicket

32 (37.6%)

 

Roots off the ground

Sapling

15 (27.8%)

Small thicket

23 (42.6%)

Thicket

16 (29.6%)

 

 

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.

Diameter classes (cm)

 

Number of trees

Number of wounds

Wound in each classes/total wounded trees (%)

Wound in each classes/total trees in each class (%)

<35

Tree length

Cut-to-length

145

 

138

42

 

32

45.6

 

39.5

29.0

 

23.0

35-50

Tree length

Cut-to-length

63

 

62

29

 

20

31.5

 

24.7

46

 

66.7

50-70

Tree length

Cut-to-length

31

 

30

15

 

14

16.4

 

17.3

48

 

32.6

>70

Tree length

Cut-to-length

14

 

19

6

 

15

6.5

 

18.5

43

 

51.7

Total

Tree length

Cut-to-length

253

 

249

92

 

81

100

 

100

46.9

 

42.4

 

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

 

 

 

 

Tree length method

 

Wound place

On root

Up to 1 m

17 (18.5%)

67(72.8%)

>1 m

8 (8.7%)

 

Wounds area

 

Degree of  wounds

<100

  26 (28.2)

100-1000

>1000

Deep

44 (47.8%)

22 (23.9%)

10 (11%)

Light

82 (89 %)

 

 

 

 

Cut-to-length method

 

Place of wounds

On root

18 (22.2%)

Up to 1 m

57 (70.4%)

<1 m

6 (7.4%)

 

Wounds area

<100

22 (27.1%)

100-1000

42 (51.8%)

>1000

17 (22.1%)

Degree of  wounds

Deep

8 (9.8%)

Light

73 (91.2%)

 

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.

 

 

 

 

Tree length method

 

Leaned

Sapling

Small thicket

27 (64%)

13 (31%)

Thicket

2 (5%)

 

Wounded

Sapling

34 (40%)

Small thicket

21 (25%)

Thicket

28 (12%)

 

Roots off the ground

Sapling

10 (44 %)

Small thicket

7 (30%)

Thicket

6 (26%)

 

 

 

 

Cut-to-length method

 

Leaned

Sapling

19 (63%)

Small thicket

10 (34%)

Thicket

1 (3%)

 

Wounded

Sapling

42 (42%)

Small thicket

30 (30%)

Thicket

27 (28%)

 

Roots off the ground

Sapling

19 (49%)

Small thicket

11 (28%)

Thicket

9 (23%)

 

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

Sig.

F

Mean Square

df

Sum of Squares

Source

0.451

0.57

254.15

1

254.15

Harvesting method

<0.001

9.03

4030.31

2

8060.62

Tree growth stage

0.652

0.43

190.91

2

381.82

Harvesting method × tree growth stage

 

 

446.35

405

180771.85

Error

 

 

0

411

189456.33

Total

 

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.

Sig.

F

Mean Square

df

Sum of Squares

Source

<0.001

18.46

127.32

1

127.23

Harvesting method

0.006

7.23

49.87

2

99.75

Tree growth stage

0.048

3.68

25.46

2

50.93

Harvesting method tree growth stage

 

 

6.89

16

110.34

Error

 

 

0

22

8866

Total

 

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


DISCUSSION

One of the most important issues in harvesting, except when clear-cutting is used, is logging damage to residual stands. Usually in the harvesting procedure, tree damage is to be expected and unavoidable, especially in mature, fully stocked stands. Many researchers worked on finding differences between traditional harvesting and well organized harvesting under comparable conditions. The results of all of these studies showed that in well-organized harvesting system, damage to residual stand decreased significantly (Hedin 1980; Garland 1997, Sist et al. 1999; Pinard 2000; Sobhani 2001; Jackson 2002).

The results of this study showed that the harvesting operation may cause significant damages to the remaining trees and regenerations.  By the well-designing and constructing skid trails before harvesting operation, only limited area will be ready for wood extraction, while by applying directional felling, trees are winched along strips. The risk of damage to the boundary trees is low on such trails. In the skid trails, straight line and higher curve radius is an important issues.

Han and Kellogg (2000) stated that dimension of skidder and the load size were the most significant variables in the damage to residual stand. Therefore, they recommended that the width of skid trails should be between 3.6-4.2 m which depends mostly to the harvesting methods. In the study, the width of the skid trail was considered 4 m for both methods.

 

Therefore it need to be considered wider skid trail besides being straight and higher curve radius.

The present study showed that damage to residual stand as well as regeneration in winching strips and also skid trail in the tree length method was less than those in the cut-to-length method. This may related to the higher number of skidded logs in the cut-to-length method in comparison with tree length method. In both methods, the amount of damage to sapling was less than in thicket and small thicket. The main reason for that was the higher flexibility and ability to be leaned against higher pressure in sapling. Overall, damages to winching strips were 18% and 28% in the skid trail which were higher than the results of Nikooy (2007), Mousavi Mirkala (2009) and Tavankar & Bonyad (2012).

Many scientists showed that features such as location of wound on standing trees, wounds area, and deepness of wounds are the most important factors for measuring damage to residual stand (Stone & Coulter 1975; Wasterlund 1992; Bettinger & Kellogg 1993; Han & Kellogg 2000). Therefore, in the present study, evaluations of damage due to cut-to-length and tree length methods on the residual stand were compared applying the same factors. The present study showed that in both methods, the number of wounds on the trees in winching strip and skid trail in a height less than 1 m were higher than those in roots and over one meter height. These wounds have negative effect on residual stand due to increasing chance of decay (Shea 1960).  

The wounds on the injured trees are located in different areas. In most of the cases, the injuries were situated up to 1 m above the stem which represents the most valuable part of the tree. In spruce stands, harvested by partial and shelter wood cutting, only 15% of all trees wounds were situated above 0.5 m, with over 60 % of the trees being damaged at the root collar (Vasiliauskas 1993). In this study, about 88% of wounds were located up to 1 m (wounds on root are also included). The number of wounds on the damaged trees varied considerably; hence they were classified into three categories.

Overall (along skid trails and winching strips in both methods), 44 % of all the damaged trees had 1 wound, while 38.0 % had 2-3 wounds, with the remainder (18.0 %) having more than 3 wounds. For all the damaged trees, 18.6 % of damages were located on the roots, 71.0 % below 1 m of the stem excluding roots, while 10.4 % located above 1 m.

The sizes of the logging wounds reported in several ways. In the North American conifer forests, scar sizes on damaged trees ranged from 0.13 cm2 to 2968 cm2 (Bettinger & Kellogg 1993). In the study by Vasiliauskas (1993), the size of logging wounds on Norway spruce Picea abies reached 1000-3500 cm2. In the present  study, overall (along skid trails and winching strips in both methods) 33 % of wound areas covered less than 100 cm2, 48 %  varied between 100  and 1000 cm2,  while 19% were larger than 1000 cm2. Comparing the methods showed that the tree length method leads to larger wound than the cut-to-length method.

The distribution of different damage size showed similar results with previous studies (Nikooy 2007; Mousavi Mirkala 2009). Most trees wounded during forest operations are not randomly distributed within a stand, rather they are situated close to the skid trails and winching strips (Bettinger & Kellogg 1993; Nikooy 2007). Siren (1982) noted that 90% of wounded stems located less than 5m away from the centerline of the extraction route. In the present study, in both methods, wounds were mostly (around 80%) up to 1m away from borderline of skid trail or centerline of winching strip.

As a conclusion, damage to residual stand was significant in the study and was lower in the tree length method than in the cut-to-length method. The most reason for higher damage in the cut-to-length method may be associated with the higher number of winched or skidded logs in each cycle which increases the chance of strike to border trees.

 

ACKNOWLEDGEMENTS

I would like to thank to Dr. Ramin Naghdi (Faculty of Natural Resources, University of Guilan) for their help and arrangement the study area. Thanks to Dr. Nikooy (Faculty of Natural Resources, University of Guilan) for providing related material for the research. The study was not financially supported by any individual, group or organization and was done as my personal interest for completion of my previous study in the area. Thanks to Agnese Priede for editing the text and improving the English in the manuscript.

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