The concept of opening up forests by a permanent road network as a precondition for forest management and utilization of forests in a sustainable manner is widely accepted both to specialists and to the public at large, but it is a difficult concept to put into effect. This is particularly true in steep and difficult terrain of the East Himalayan range in Bhutan where forest stands not only sustain site productivity but often serve special protective functions. Avoidance of site disturbance is imperative.
Growing concerns on environmental issues and the fact that forest roads are unquestionably the most damaging features of timber harvesting operations (FAO, 1996) demand replacement of purely technology-oriented solutions by holistic, interdisciplinary approaches of forest infrastructure development that take account of the need for landscape, watershed and wildlife considerations.
Another important fact to be considered in road planning activities in remote rural areas of Bhutan is that in many cases forest roads do not just serve timber harvesting purposes but have become an essential component of the local level development infrastructure. Forest roads, therefore, should be seen as part of a well-planned rural road network to be developed and should contribute to Sustainable Alpine Land Management which meets the needs of the agriculture and forestry sector while serving other current and anticipated demands.
Equal attention should be paid to the three phases of road projects (Litzka and Haslehner, 1995), namely, planning and design, construction operation, and integration which comprises bioengineering as well as landscaping measures. Whereas planning and construction phase improvements have taken place in Bhutan, integration measures are still reluctantly applied in forest road projects.
The general layout of the forest road network as the basic component of the transport system varies considerably due to many factors such as:
Although there are some typical patterns and designs for certain terrain features, the forest road network of the FMUs in Bhutan will have as much diversity as the terrain itself. The planner's main objective is to find a feasible and economical system with the lowest cost in the long run while serving the needs of multiple-use management and environmental protection. Road planning should always be guided by the following principal considerations (Litzka and Haslehner, 1995):
any disturbance to the landscape is to be kept to the absolute minimum;
environmentally sound correction of poorly located and designed roads at a later stage is virtually impossible;
reckless and incompetent construction work may destroy the beneficial effects of even the most carefully selected road location;
undesired effects and scars inflicted on the landscape can seldom be remedied at a later stage and only at much higher costs.
One of the first steps of the planning process is to fix the boundaries of the area for which the transport system is to be developed. This area is referred to as “logging area” when covered by forest. The boundaries will normally correspond with those of the watershed marked by ridges in mountainous terrain. Unless the valleys are virtually inaccessible or the slopes are too unstable, the forest road network should be developed from the lowest points of the logging area to take full advantage of the force of gravity for timber transportation (Sedlak, 1985a).
Due to the steep and difficult terrain conditions in most FMUs in Bhutan and due to the special protective function of certain watersheds, only about one-third or even less of the total area of certain FMUs can be considered as productive forests where harvesting operations will take place like in the FMUs of the TFDP (Roetzer, 1996). The main challenge under these circumstances for the planning engineer is to develop a transportation system which serves both the need to keep site disturbance to the absolute minimum and to provide forest access for active management.
As long-distance cable systems can substitute partly for roads, they are considered a solution for steep mountainous terrain to keep the road density low and to minimize site disturbance. The maximum logging distance with such a cable unit is about 1 600 m, requiring a road density of only 5–7 m/ha or less if slopes are long and roads lead through the middle of the forest (Roetzer, 1996). Given the fact that the long-distance cable system is almost exclusively used in Bhutan in commercial timber logging, the slopes are normally subdivided into two sections by a feeder road beginning from the main road opening up the valley.
Preliminary drafts of the general road system are normally developed in the office by means of good topographic maps with a scale of at least 1:25 000 and by viewing aerial photographs or other relevant means to draw information. To determine preliminary routings and to eliminate unacceptable variants in the office, helps to considerably reduce labour and time consuming road survey work in the field.
However, field reconnaissance by the planning engineer and the local staff in order to verify and/or correct preliminary paper locations or even to directly select feasible routes in the field, should never be replaced by studies of maps or photographs.
For many FMUs in Bhutan good topographic maps are simply not available at this time. As in the road projects under review, the existing 1:25 000 topographic sheets are just blown up from 1:500 000 scale maps (Roetzer, 1996). If so, the work begins immediately with intensive field reconnaissance to explore the logging areas in detail, to learn the peculiarities of the terrain and to select feasible road corridors.
All control points with their elevation assessed by barometric altimeters and relevant information are noted in drawing and sketches. The information is then transferred to the 1:25 000 topographic map and road lines plotted with the help of the “Divider-step method”. The planned road network should also be based on the FMU's forest management plan or at least it has to be checked and revised as soon as the management plan is available for the particular planning unit.
Photo 9. Long-distance cable crane logging will continue to be the most commonly applied harvesting system throughout Bhutan in the near future
