The TFDP, initiated in 1993 by the Royal Government of Bhutan and supported by the World Bank and the Swiss Development Cooperation, aims to bring the forests of Eastern Bhutan under sustainable management (Roetzer, 1996).
Figure 1. Administrative map of Bhutan - Mongar, Tashigang, Pemagatsel and Samdrup Jongkhar are covered by TFDP
As a first step towards this goal, six FMUs listed in Table 5 have been identified in the region, which is characterized by a great variety of vegetation zones. Ranging from Sub-Tropical Forests in the South at elevations as low as 200 m above sea level to the high altitude Fir Forests that form the tree line at approximately 3 900 m above sea level. Much of the forest in Eastern Bhutan has been cleared for agriculture and shifting cultivation.
Table 5. The FDP's forest management units (after Roetzer, 1996)
|Third Forest Development Project (TFDP)|
|Forest Management Unit||Unit area||Main forest types|
|Korila FMU||13 840 ha||broad-leaved forests|
|Khaling-Kharungla FMU||7 277 ha||broad-leaved forests, some Blue Pine and some Fir|
|Lingmethang FMU||5 750 ha||partly Chir Pine, partly broad-leaved forests|
|Geruwa-Demula (Bangtar)FMU||11 755 ha||subtropical forests|
|Lhuntse, Tangma-chu FMU||4 300 ha||(inventory not yet carried out)|
|Tashiyangtsi, Dongdi-chu FMU||9 200 ha||(inventory not yet carried out)|
|Total TFDP||52 122 ha|
All forest areas given in Table 5 are preliminary and approximate except for Korila and Khaling-Kharungla FMU where forest management plans have already been established. As mentioned in Chapter 2, because of steep and difficult terrain as well as special protective functions of certain watersheds only about one-third or even less of the total FMU areas can be regarded as productive commercial timber forest (Roetzer, 1996).
Standing volumes for certain forest types, according to results of forest inventories so far carried out, are given in Table 6 for TFDP.
Table 6. Forest types occurring within TFDP (after Roetzer, 1996)
|Forest type||(m)||(mm/year)||(m3/ha)||Species groups|
|Sub-tropical forest||200–1000||2500–5000||600–700||Sub-tropical species, some tropical genera|
|Chir pine forest||700–2000||1000–1500||about 100||Pinus Roxburghii|
|Warm broad-leaved forests||1000–2100||2300–4000||300–400||Mixture of evergreen and deciduous broad-leaved species|
|Cool temperate forests||2000–2800||2000–3000||332–335|
|- Evergreen oak forest||Quercus+Castanopsis genera;|
|- Moist broad-leaved||Mixture of broad-leaved species|
A low intensity assessment of the forest resource of Eastern Bhutan was conducted by TFDP, starting in January 1995. A systematic 15 km × 15 km sampling grid, aligned to the 5 km reference grid of the 1:50 000 scale Land Use Working Map series (LUWM) of the Land Use Planning Project (LUPP) by MoA, was laid over Eastern Bhutan. All grid points on these maps that fall in areas of natural forest (i.e. with a crown closure of more than 10 percent) and are physically accessible defined the actual sample.
In total, 36 sampling units were selected using this process (Laumans, 1995). Each unit basically consists of a cluster of four standard 0.05 ha inventory plots in a 40 m square pattern. An analysis of the first 13 sample clusters, mainly located in the Mongar, Lhuentse and Samdrupjongkha dzongkhags, cannot be considered representative of the whole area of Eastern Bhutan but gives an idea on accuracy of forest type classification based upon satellite images as carried out by LUPP.
Assuming the field assessments constitute “ground-truth”, the forest type classification on the LUWM maps used for the stratification was found to be 88.5 percent accurate overall (Laumans, 1995).
Table 7. Classification error matrix at forest type level (Laumans, 1995)
|Field||Row total||User accuracy|
Note: FCc Chir pine forest
FB Broad-leaf forest
FBc Broad-leaf with 20–40% conifers
The “user accuracy” gives the probability that a polygon assigned a certain forest type on the map is indeed this type in the field. When taking the crown closure into consideration, the overall accuracy is reduced to approximately 60 percent (Laumans, 1995). For 34 plots (65 percent) the crown closure classes assessed in the field were the same as on the LUPP map, lower in the field for 16 plots (31 percent) and lower on the map for two plots (4 percent).
Table 8. Classification error matrix at crown closure class level (Laumans, 1995)
|Field||Row total||User accuracy|
|Note:||LUPP classes 2 and 3 are combined since they were not separated during field assessment|
|FCc||Chir pine forest||class 1||10–40% crown closure|
|FB||Broad-leaf forest||class 2||40–80 crown closure|
|FBc||Broad-leaf with 20–40% conifer||class 3||>80% crown closure|
This reduced accuracy, with the maps overestimating the crown closure in about one-third of the cases, did not directly affect the stratification for the inventory since the crown closure classes had not been considered in the stratification (Laumans, 1995), but could indirectly affect the overall results. The actual total forest area might be reduced if forest presently mapped as having a crown closure of 10–40 percent actually turns out to be non-forest in the field (i.e. having a crown closure of less than 10 percent).
For the error matrices presented above it should be noted (i) that the plots are taken as clusters of four and are therefore theoretically not independent, (ii) that the inventory data processing has not yet covered important forest types such as Fir forest (FCf) and Mixed Conifer Forest (FCm), and (iii) that the above tabulations assume the field observations to be correct, with the field location corresponding accurately to the map location.
Table 9 gives general information on the planned and established road network of the FMUs where the distinct construction practices were studied. More detailed information on a particular work and time study road project is given in Table 10.
The starting point of the Kharungla road is located about 5 km north-east of Wamrong on the national highway at an altitude of approximately 2 240 m. The first stretch of about 800 m leads north-westward, up and across a ridge at 2 320 m altitude (Roetzer, 1995). Although the terrain of this section cannot be regarded as difficult, it is considered quite sensitive for construction since it leads through steep terrain just above the national highway which should not be affected by falling construction materials.
Table 9. General description of road net of FMUs under review
|Project feature||Planned road network|
|Forest management unit||Khaling-Kharungla FMU||Korila FMU|
|Location||Kurchilo block, comp. II/III||Ngatshang/Korila block|
|Forest area opened up||approx. 800 ha||approx. 670 ha|
|Altitude range of forest||2100–2800 m||1000–2000 m|
|Total road length||8052 m||6700 m|
|Road density||10.1 m/ha||10.0 m/ha|
On the opposite side of the ridge the road leads into the forest which extends towards the west along slopes with a south-western aspect and ends at the western boundary of the Kharungla FMU at an altitude of 2 480 m. The terrain conditions are characterized by extended stretches of slopes with gradients between 40 and 80 percent, interrupted by frequent ravines often with vertical rock outcrops requiring blasting.
These terrain conditions and the narrow allowable range of gradient for a forest road resulted in a number of difficult stretches leading through slopes above 100 to 120 percent side gradients and across some short, almost vertical rock surfaces (Roetzer, 1995).
In comparison, the terrain conditions of the Korila road Nr. 1, referred as “Korila road” below, were regarded as easy in general, with few problem areas of steep slopes but without solid rock requiring blasting (Roetzer, 1994). The road leads off the national highway, about 30 km east of Mongar, more or less following the contour-line towards the west with road gradients between 3 and 6 percent. The road ends at a distinct flat cleared area at an altitude only 17 m higher than its starting point at the national highway.
The first 900 m of the Korila road opens up degraded forest whereas the remainder leads through almost unlogged forest. The forest near the starting point has been degraded by production of construction wood as well as fuelwood for local use, and overgrazing. Both are often found along the national highway, approximately 200 m above and below the road and in the vicinity of settlements.
According to the technical reports of the road projects, drainage from the road surface should be provided by a crowned road, a hillside ditch and culverts with diameters from 40 to 60 cm, spaced at distances from 80 to 120 m depending on the road gradient. The 80 m spacing should meet the requirements of road stretches with a gradient of 11 percent. In road sections where intermittent streams are to be crossed, the dimension and spacing of planned culverts were adjusted to the actual need for adequate water drainage.
On the Kharungla road project, 15 intermittent streams were planned to be crossed by culverts with a diameter of 90 cm, two pipes side by side, nine by culverts of 60 cm in diameter and four to be crossed by fords (Roetzer, 1995). In comparison, on the Korila road project 21 culverts with a diameter of 90 cm have been recommended as well as two fords (Roetzer, 1994).
The main features and road standards as suggested by the planning engineer are stated below.
Table 10. Main features of the road projects
|Project features||Kharungla road||Korila road No. 1|
|Natural forest||approx. 800 ha||approx. 290 ha|
|Degraded forest||---||approx. 130 ha|
|Road length||8 100 m||2 900 m|
|Difference in altitude:(starting-end point)||240 m||17 m|
|Bedrock material||phyllite||phyllite with limestone layers|
|Streams to be crossed||28 intermittent streams||23 intermittent streams or marshy areas|
|Fords/bridges||4 fords||2 fords|
|Construction equipment||1) excavator||1) bulldozer|
|2) pneumatic drilling equip.||2) pneumatic drilling equip.|
|3) dump truck||3) dump truck|
|4) backhoe*||4) backhoe*|
|5) grader/road scraper*||5) grader/road scraper*|
|6) vibration roller*||6) vibration roller*|
|7) stone crusher*||7) stone crusher*|
|gradient <80%||5 700 m||2 530 m|
|80–100%||1 800 m||270 m|
|(partly vertical) 100–120%||600 m||90 m|
|Max. road gradient||11%||6%|
Note: *) Equipment recommended by the planning engineer but actually not employed
Although recommended in the technical report of the Korila road, no slope revegetation measures had been undertaken to stabilize cut and fill slopes in order to prevent erosion. In general, the cut slopes provided by bulldozer were too steep either for natural or man-made revegetation without correction of slope gradients.
By contrast, in road construction by excavator at least the fill slope will be protected by a debris cover and soil surfaces exposed to erosion will be substantially reduced. Retaining structures will be built up with boulders by the excavator wherever needed for slope stabilization alongside the road (for details see Chapters 3.2 and 3.7).
The extension of the Korila road, referred to as “Korila extension” below, where the bulldozer construction work was observed by work and time studies is somewhat less favourable with regard to conditions for road construction. This segment is characterized by stretches of difficult terrain where bulldozer construction is considered inappropriate due to site and stand damage on a significant scale (see Photo 5).
Photo 5. Full bench construction with side cast material is the most common bulldozer technique with the potential of making large areas unproductive and inflicting scars on the landscape
Minor rock outcrops were removed manually, others by means of explosives. The use of a hydraulic excavator simply equipped with a rock bucket could have avoided or at least considerably reduced both, the damage to adjacent timber stands and rock disintegration either performed manually or by explosives. Furthermore, stump blasting had been recommended as bulldozers without adjustable rippers are rather limited in use for stump removal. The stumps were often prepared manually by digging out or cutting off roots for subsequent removal by bulldozer.
Since the use of a backhoe to correct slope gradients is not planned for the Korila extension, the cut and fill slopes will remain as established by the bulldozer with some improvement by manual removal of the overhang at the top edge of the cut slopes (Photo 6).
Photo 6. Removal of the overhanging forest floor and tree stumps at the top edge of the cut by labourers simply equipped with iron bars at the bulldozer construction site
At the bulldozer construction site a very poor practice of dealing with obstacles during the ongoing construction process was observed. The bulldozer operator tried to bypass stumps or rock wherever possible and left the marked grade line. This practice resulted not only in an unacceptable change in road location but also in road gradients too shallow for proper water drainage from the running surface.
Figure 2. Regular cross-section for earth and rock
The cross-section both for earth and rock recommended in the technical reports of the Kharungla and Korila road projects is shown in Figure 2. The same regular cross-section applies to the Korila road extension. Figure 3 shows the actual cross-sections found at the study sites of the Kharungla road and the Korila road extension which are derived from several measurements spaced at 30 m distances along the road centreline of the road sections where construction operations had been observed.
Figure 3. Actual cross-sections at study sites
As one can see from Figure 3, in road construction by excavator at the Kharungla study site, the average subgrade width was in compliance with the subgrade width requested by the planning engineer for anticipated safe use by heavy timber trucks or other types of machinery. By contrast, in bulldozer construction at the Korila extension study site, the subgrade width has not only been decreased to 4.5 m on average, but also varies in a significant range from 3.9 to 4.8 m due to poor construction practice and lack of supervision (for details see Chapter 8.2).
With regard to road construction equipment it should be mentioned that even for the Korila road with more favourable conditions for road construction, a hydraulic excavator was considered the most suitable equipment by the planning engineer in order to comply with best environmentally sound road construction practice. The second choice was a traxcavator which is a track type loader capable of excavating and loading (Roetzer, 1994). Its use would have allowed short distance transportation and a more careful deposition of excavated materials.
Being aware of the fact that the equipment most likely to be used would be a bulldozer, the use of a small excavator or at least a backhoe attached to a agricultural tractor was recommended by the planning engineer in order to correct unsatisfactory shaped cut slopes, avoid cut slides and facilitate revegetation of cut slopes.
Unfortunately, none of the suggested additional equipment was used for the Korila road and its extension. However, some correction of the cut slopes have been provided manually by removal of the overhanging forest floor and tree stumps at the top edge of the cut slope (Photo 6).
Furthermore, instead of applying suitable gravel to the running surface and subsequent shaping by grader or road scraper, the traditional way of surfacing with hand-placed rocks of a size up to 30 cm (see Photo 7) and comparatively thin layer of finer material on top has been carried out. According to personal information obtained from staff of FDC, the Korila extension will be the last road where the traditional surfacing practice will have been applied.
Photo 7. Traditional way of surfacing with rocks at the Korila extension construction site
Along the Korila road, commercial timber harvesting by long-distance cable crane started in October 1995 after completion of the road. According to the Korila forest management plan, 25 ha will be harvested and replanted annually (Roetzer, 1994). It has been decided that all forests above and below the Korila road, both, the degraded stands mentioned earlier as well as the unlogged timber stands, will be clear-felled and the areas replanted with a number of indigenous species to avoid monocultures.
The area clear-felled per crane set-up, referred to as a corridor below, shall not exceed 9 ha, the minimum distance between the corridors must not be less than 100 m (Roetzer, 1994). Although it was planned to observe the crane set-up and the ongoing logging operation in corridor 9 by time and work studies, only one day of the ongoing cable logging operation could be studied in corridor 8 due to a major delay of the logging operation.
To improve the information on cable logging, another day of cable crane operation was observed and data collected in the Chamgang-Helela FMU in Western Bhutan. Information on the logging sites, where time and work studies on long-distance cable crane operation were carried out, is listed in Table 11.
Photo 8. Long-distance cable systems can substitute partly for roads. They are a solution in steep mountainous terrain to keep the road density low and consequently reduce site disturbance
Table 11. Features of the logging sites
|Project features||Korila logging site||Helela logging site|
|Forest management unit||Korila FMU||Chamgang-Helela FMU|
|Timber stand||mature stand of broad-leaved species||over-mature coniferous stand (Hemlock, few scattered fir)|
|Silvicultural treatment||strip-wise clear-felling||group selection felling|
|Length of cableway||863 m||613 m|
|Timber volume to be logged||1 023 m3||no information|
|Number of supports||4 supports||1 support|
|Lateral pulling distance||up to 30 m||up to 30 m in cleared plots, up to 2 m along cableway|
|Area without old growth||approx. 5.2 ha||approx. 0.8 ha (2 plots of 0.3 ha; along cableway 0.2 ha)|
|Location of road||in the middle of slope||at the bottom of slope|