4. COMPARISON OF PRODUCTIVITY, COST AND ENVIRONMENTAL IMPACT OF CONVENTIONAL AND REDUCED IMPACT TIMBER HARVESTING

This study analyses productivity, costs and environmental impacts of conventional and reduced impact timber harvesting. It was conducted by D. Losuh (1996) and H. Sularso (1996) for their thesis (S2) as post graduate students in Bogor Agricultural University under supervision of the author. The main objectives of the study were to collect information on productivity, cost and environmental impact associated with timber harvesting operations in the tropical natural forest in Indonesia and to test the applicability of the FAO model code of forest harvesting practice (D.P. Dykstra and R. Heinrich, 1996).

The research was conducted in the forest concession area of PT. Sumalindo Lestari Jaya IV in Berau Regency, East Kalimantan, Indonesia. In order to achieve the objectives, the study area was divided into two blocks. Each block was 10 ha, consisting of 10 plots of 100 m x 100 m; Block A for conventional timber harvesting and Block B for reduced impact timber harvesting.

Figure 4 shows the design of the research blocks and plots.



Figure 4. Research blocks and plots

The personnel or crews involved in the timber harvesting system used in conventional and reduced impact timber harvesting were the same and were as follows:

· felling by chainsaw operator with heavy chainsaw (8 HP, 12 kg, 5.97 kW), assisted by a helper;

· winching and skidding by operator of crawler tractor (215 HP/2,000 Rpm, 160 kW), equipped with winch and cable of at least 30 m and diameter of 1¹/₈ inch (28.6 mm), assisted by a helper;

· bucking of logs by chainsaw operator at the landing with heavy chainsaw;

· debarking of logs by a 4 - 6 man-team at the landing with crowbar;

· loading of logs at the landing by wheeled loader (291 HP/2 ,100 Rpm, 217 kW);

· hauling by truck-trailer (300 HP/2,500 Rpm, 224 kW); and

· unloading at logyard for river transport or at industrial plant with wheeled loader (291 HP/2,100 Rpm, 217 kW).

The data collected included:

· tree location and contour mapping;

· tree volumes and timber volume extracted;

· time used in felling and skidding;

· labour and equipment costs;

· residual stand damages; and

· opening gaps.

4.1 Productivity

The productivity of the conventional and reduced impact timber harvesting was examined by conducting a detailed time study and work analysis of all phases of harvesting operations, including felling, skidding, bucking, loading, hauling and unloading activities. The productivity was calculated by using the following formula:

where:

p = productivity (m³/hour)

v = wood volume (m³)

t = working time (hours)

Table 6 shows the results of the time study for felling in conventional and reduced impact timber harvesting. Although the productivity of felling in reduced impact harvesting is lower than in conventional timber harvesting, the differences are very small, namely only 4.05 %.

These differences were caused by the average diameter of the harvested trees in conventional timber harvesting (68.42 cm), bigger than average diameter of the harvested trees in reduced impact timber harvesting, and because the amount of harvested trees with buttresses in reduced impact harvesting was more than in conventional timber harvesting.

Table 6. Time required and productivity of felling in conventional and reduced impact

timber harvesting

The average time needed for felling in conventional timber harvesting for tree with buttress is 24.24 minutes per tree and for tree without buttress is only 14.17 minute per tree. In reduced impact timber harvesting, the average time for felling trees with buttresses is 21.88 minute per tree and for trees without buttresses is only 15.82.

Therefore the productivity of felling in conventional timber harvesting for trees without buttress is 11.88 m³/hour, for trees with buttress is 17.63 m³/hour; in reduced impact timber harvesting the productivity of felling trees with buttress is 18.34 m³/hour, and trees without buttress is 10.15 m³/hour.

The detailed data of time study on felling in conventional and reduced impact timber harvesting can be found in Appendix 1.

Table 7 shows time required per round trip and productivity of skidding in conventional and reduced impact timber harvesting. The productivity of skidding in reduced impact timber harvesting is higher than it is in conventional timber harvesting (about 12.98 %).

The time required for construction of skidtrail in reduced impact timber harvesting is 3.61 minutes/m³ of harvested log.

Table 7. Time required per round trip and productivity of skidding in conventional and

reduced impact timber harvesting

* not including time required for skidtrail construction

The detailed data of time study on skidding can be found in Appendix 2 for skidding in conventional harvesting and in Appendix 3 for skidding in reduced impact timber harvesting.

4.2 Cost

The production costs of timber harvesting with conventional and reduced impact timber harvesting methods are calculated based on fixed cost (depreciation and interest) and variable cost (repair and maintenance, petrol oil and lubricants, and wages of labourers).

Table 8 shows the comparison of the production cost of felling, skidding, bucking, loading, hauling and unloading in conventional and reduced impact timber harvesting. The total cost of timber harvesting in conventional timber harvesting is Rp 28 081.29/m³ while in reduced impact timber harvesting it is Rp 28 264.62/m³.

The reduced impact timber harvesting increased the average cost of timber harvesting by 1.26 %, which is caused by the skidtrail construction cost. The reduced impact timber harvesting cost here does not include the topographic maps and timber harvesting planning costs.

The comparison of tree damages value caused by conventional and reduced impact timber harvesting shows that with an assumption of a profit ratio of 30 %, the timber damages value caused by conventional timber harvesting is twice greater than the timber damages value caused by reduced impact timber harvesting (Rp 28 241.68/ha : Rp 12 433.42/ha). Table 9 shows detailed data of timber damages value caused by conventional and reduced impact timber harvesting.

Table 8. Production costs of conventional and reduced impact timber harvesting

Table 9. Damages value caused by conventional and reduced impact timber harvesting

Note : D = V_rs x NT; D = Timber damages value (Rp/ha); V_rs = Volume of timber damages

caused by timber harvesting (m³/ha); NT = Stand value (Rp/m³)

Reduced impact timber harvesting is not more expensive than conventional timber harvesting and is economically profitable, because reduced impact timber harvesting will enhance future forest productivity and reduce the costs associated with potentially adverse off-site consequences of timber harvesting (erosion, sedimentation, hydrological cycle, etc.).

4.3 Impact on the residual stand

Residual stand damage caused by timber harvesting with the TPTI system means that the damage, which occurs in part of the stand, consists of tree damages and soil/areas damage.

The types of tree damages or injuries consist of (see Photo 14):

· crown damage

· broken tree

· fallen tree

· bark and stem injury

· root and buttress injury

The soil/areas damage consist of soil compacting and opened areas caused by felling and skidding (see Photo 15).

The degree of tree damages in the residual stand can be calculated as based on injury size of tree as well as based on population of trees as follows:

A. Based on injury size

1. Heavy injury

a) broken stem

b) fallen tree

c) crown damage : > 50 %

d) bark and stem injury : > 50 % stem girth

e) root and buttress injury : > 50 % buttress or root

2. Medium injury

a) crown damage : 30 - 50 %

b) bark and stem injury : 25 - 50 % stem girth

c) root and buttress injury : 25 - 50 % buttress or root

3. Light injury

a) crown damage : < 30 %

b) bark and stem injury : < 25 % stem girth, length < 1.50 m

c) root and buttress injury : < 25 % buttress or root

B. Based on population of trees:

1. heavy damage : trees with _ 10 cm dbh and more > 50 %

2. medium damage : trees with _ 10 cm dbh and more 25 - 50 %

3. light damage : trees with _ 10 cm dbh and more < 25 %

Degree of residual stand damage (_ K) :

where:

R = number of damaged trees with a diameter of 10 cm and more after timber harvesting

P = number of trees with a diameter of 10 cm and more before timber harvesting

Q = logging intensity (number of harvested trees per ha)

Tree damages are generally caused by felling and skidding activities. The degree of residual stand damages based on tree population and the stage of vegetation development caused by conventional and reduced impact timber harvesting was found as in Table 10.

Table 10. Degree of residual stand damages based on tree population and stage of vegetation development

The results of the study show that reduced impact timber harvesting can reduce up to 50% of tree damages otherwise caused by conventional timber harvesting.

Based on the injury size of individual trees, the degree of tree damages caused by conventional and reduced timber harvesting was as in Table 11.

Table 11 shows that the injury size of each individual tree caused by reduced impact timber harvesting is smaller or lighter than by conventional timber harvesting. Most of the damaged trees were heavily injured (ca. 70-80%).

Table 11. Degree of tree damages based on the injury size of individual trees

(...) degree of tree damage based on tree population

Table 12 shows the types of tree damages caused by felling and skidding operations in conventional and reduced impact timber harvesting.

The size of the opened area caused by felling depends on the timber harvesting intensity. The higher degree of timber harvesting intensity causes the larger opened area of the residual stand.

Table 13 shows the size of opened areas caused by felling activities based on timber harvesting intensity in conventional and reduced impact timber harvesting.

The size of the opened areas caused by felling of one tree in conventional timber harvesting is 300 m² and in reduced impact timber harvesting is 212.90 m². With a timber harvesting intensity of 3 - 4 tree/ha, the opened areas caused by felling in conventional timber harvesting is 11.10 % and in reduced impact timber harvesting is 7.65 %.

Table 12. Types of tree damages caused by felling and skidding in conventional and

reduced impact timber harvesting

(...) Degree of damage based on tree population

Table 13. Sizes of opened areas caused by felling in conventional and reduced impact

timber harvesting

Table 14 shows the size of opened areas caused by skidding operations based on timber harvesting intensity and conventional and reduced impact timber harvesting. The size of the opened areas caused by skidding of one tree in conventional timber harvesting is 235.82 m² and in reduced impact timber harvesting is 144.67 m².

With the timber harvesting intensity of 3 - 4 tree/ha, the opened areas caused by skidding in conventional timber harvesting is 8.73 % and in reduced impact timber harvesting is 5.21 %.

The degree of the opened areas in the residual stand caused by felling and skidding with a timber harvesting intensity of 3 - 4 tree/ha in the conventional timber harvesting is 19.83 % compared with reduced impact timber harvesting which is only 12.88 %. Therefore, reduced impact timber harvesting can diminish by up to 35 % the opened area otherwise caused by conventional timber harvesting.

Table 14. Sizes of opened areas caused by skidding in conventional and reduced impact

timber harvesting