Conventional timber harvesting operations are as described in Chapter 2, which is still a very common practice in the natural tropical rain forest in Indonesia. The felling and skidding operations conducted are not based on a timber harvesting plan (climber cutting, skidtrail network layout, directional felling, winching etc.), and also are not based on tree location and topographic map; generally these activities are uncontrolled.
Reduced impact timber harvesting is based on forest prospecting prior to harvesting, and uses this data to design a layout of felling compartments and inventory units, and also to plan the timber harvesting operations (J. Hendrison, 1990). A tree location and topographic map used for the harvesting plan map serves as a guide for the felling and skidding crew in timber harvesting operations.
Knowledge on field condition, harvestable trees and nucleus trees distribution, mother trees, protected trees and protection areas within a working area are the keys to selective harvest control in the TPTI system. Therefore, a Stock Map (Tree Location) and Contour Line Map with large scale (1:2,000) from 100 % cruising result of trees with a diameter of 20 cm or more is needed for planning a skidtrail network as well as for directional felling plans. The contour lines interval is 5 m. The preparation of the Tree Location Map and Contour Line Map should be done in the TPTI system two years before the timber harvesting operation. Figure 2 shows an example of Tree Location and Contour Line Map, scale 1:2,000. The reason for using a map with a scale of 1:2,000 is that with scale 1:2,000 the map for one compartment (_ 100 ha) is both easier to use and bring into the forest by the chainsaw and tractor operators.
Figure 2. An example of a tree location and contour lines map (scale l : 2,000)
In timber harvesting operations, the forest enterprises should exclude some restricted locations within their working areas where timber harvesting is prohibited, such as in the following areas:
· radius of 200 m from the edge of a water springs;
· at minimum, 100 m from the edge of a lake or coast measure from the highest tide toward the coast;
· at minimum, 100 m from the sides of a river and 50 m from the sides of a creek;
· near the edges of steep lands (> 40%) to at least twice of those lands; and
· conservation and research areas.
Forest enterprises are expected to adhere to restrictions mentioned above on areas within concessions where they are allowed to harvest trees. These restriction areas should be excluded from the cutting area; they should be delineated on the timber harvesting plan map and marked in the field as protection areas.
The cutting of vines can reduce felling damages, since tree crowns are not bound one to another by vines. According to D.P. Dykstra and R. Heinrich (1996), in forests where climbers tend to bridge across tree crowns, climbers should be cut well in advance of the felling operation so that they will die and become brittle. This reduces the possibility of a felled tree pulling over neighbouring trees as it falls.
Therefore, it is recommended in the TPTI system, that all vines with a diameter > 2 cm be cut two years before timber harvesting. However, vines in protection areas and some species which are useful to protected animals are not to be cut. This operation could be undertaken at the same time as the inventory of the forest stand is initiated. Photo 8 shows some vines which exist beside the harvestable trees in the tropical natural forest in East Kalimantan, Indonesia.
The actual planning of the forest roads, landings and skidtrails is made on the Tree Location and Contour Line Map. Efficient access to the trees to be harvested can be accomplished by considering factors such as skidding on steep slope, stream crossings, protection areas, and by minimising the length of skidtrails by aligning an efficient skidtrail network.
Skidtrails should be constructed as straight as possible, curves and turnings should be avoided and only inserted for reaching those logs to be skidded; steep areas, valleys/swamps, rivers and unstable areas should also be avoided. The skidtrail should end with a suitable angel to the road, and skidding direction should go up or along the side of the slope. Adverse grades should not exceed 25_.
Average skidding distance of timber extraction by crawler tractors, skidtrail length and optimal distance between the haul roads depend on many factors. In general, the average skidding distance may range between 250-350 m, with the spacing of the main skidtrail between 50-100 m.
Figure 3 shows an example of a haul road, landing and skidtrail layout.
The haul road and landings should be planned, staked on the ground and built one year before timber harvesting operations. The staking and marking of the skidtrail routes should be done after road building and constructed just before felling operations are started.
Figure 3. An example of haul road, landing and skidtrail layout
3.1.5 Felling pattern and felling direction planning
Tree felling direction is planned by considering the safety of the feller, the field situation (damaged residual stand, harvested trees and regeneration), tree position, log skidding and the transportation system. The best felling direction is towards or opposite the skidtrail and should be at an angle between 30_-45_ (herringbone pattern) in relation to the skidtrail, or such that a tree falls in a straight line position to the skidtrail with the felling direction opposite the skidding direction (see Photo 9). Field conditions, the position of tree to be cut towards the skidtrail and tree height determine the felling direction towards or away from the skidtrail. The felling direction is towards the skidtrail if the harvested tree's crown does not disturb the skidding activity and its branchless stem does not lie across the skidtrail.
Essentials that should be considered in planning the felling direction are as follows:
· If possible, the tree felling direction should be aimed towards an open site and preferably some trees should be felled in the same gaps. (The felling direction of a tree that is cut should be towards the crown of a tree that has been cut earlier.)
· On a steep area, the felling direction should not be downward of the slope, but upward or to the side of the slope (along the contour).
· It should be avoided that trees fall across rivers and creeks and disturb the protection areas.
· The felling direction should not result in broken stems (for instance, falling on stones, stumps or ditches) and should not damage nucleus trees, protected trees and regenerations.
Skidtrail marking and opening is done before the felling operation. The skidtrail network is planned first on the topographic and tree location map and then in the field by using a compass, clinometer, paint or flagging tapes. The trees are marked with paint or flagging tapes are tied around trees along the proposed skidtrail route. When this is completed, the chainsaw operator cuts all trees with a diameter of 15 cm, or more, that are located at the prospective skidtrail that has been planned and marked with paint or the flag tape. The felling direction of the trees cut for the skidtrail opening should not damage nucleus trees, protected trees, or regenerations as well as disturb the skidtrail construction by the tractor operator. The felling begins from the end of the prospective skidtrail, with the felling direction away from the landing (see Photo 10). After the skidtrail route is cleared from undergrowth and trees, the chainsaw operator/feller can start to fell trees to be harvested. The felling pattern is to start from trees on the down-side to the trees on the up-side.
After the felling operation is completed, aligning of skidtrail takes place by the crawler tractor following the projected and opened routes on the ground and on the maps. The skidtrail width should not be more than 4.5 m. The crawler tractor operator will then remove all fallen trees which may block the skidding operation and clear the skidtrail. Non-disturbing stems and branches are left on the skidtrail (see Photo 11). After the construction of the skidtrail, the skidding operation proceeds.
As mentioned above, the felling begins after the skidtrail has been opened (trees cut on the skidtrail surface). The timber harvesting plan map should be brought into the field and kept by the chainsaw operator. The feller uses the map and the opened skidtrail network in order to make the final decision on the felling direction.
The felling pattern always starts from trees on the down-side and then proceeds to the trees on the up-side. The felling should be started and carried out according to the indicated felling direction on the map or trees to be harvested. For example, it should start from the closest to the landing and then proceed to the next section. The preparation for felling should be focused on work safety, ergonomics and efficiency. The felling should be preceded by clearing the surrounding area of groundcover and lianas. If the trees have buttresses, they should be removed first or not (buttresses sometimes can help control directional felling); notch and backcut should be as low as possible (see Photos 12 and 13).
Once the tree has been cut, the crown of the tree is cut off and bucking is carried out in compliance with the bucking and grading rules and in order to maximise the volume and value of the harvested trees. Therefore, before cutting the stem, its entire length should be measured and cut according to the standard set by manufacturers. After bucking, the logs should be cleaned of branches and buttresses.
The skidtrail is opened by chainsaw operator and then constructed by crawler tractor operator according to the route planned and marked on the ground. For winching and skidding operations, the crawler tractor should be equipped with a winch with a cable length of at least 30 m and a diameter of the cable of 11/8 inch (28.6 mm).
The skidding starts with the nearest log from the landing. The winching and skidding operations proceed as follows:
· The empty crawler tractor is driven from a landing on the skidtrail and is placed in an appropriate position to be able to winch in the log or logs.
· The helper pulls the winch cable out and sets the choker(s) at the log(s) some 0.5-1.0 m away from the log end.
· The helper moves to a safe place and signals to the tractor operator to start winching.
· After winching, the log load is skidded on the skidtrail to the landing. During skidding operations, the crawler tractor is restricted to move along the skidtrail and it should be ensured that its blade does not cut or touch standing trees and the soil surface.
Once timber harvesting operations are terminated, further measures should be taken to prevent environmental damages; these should include the following:
· Construction of drainage on skidtrails, landings as well as specifically where the soil is effected and where mud puddles exist.
· Cleaning of stream or waterways where the tractor crosses or where felled trees cross water flows.
· Before all wood harvesting crews abandon the harvesting area, erosion and run off preventive measures should be established at the skidtrails and landings. It is necessary that skidtrails and landings be rehabilitated by regeneration plantings - e.g. of fast-growing species or grass.