All operations undertaken to open up and manage a forest are to be guided by the consideration that unless the forest is left in a condition that will permit the attainment of a desired future condition, sustainability cannot be assured.
Regardless of the type of road construction and logging equipment used in a particular project, harvesting operations can cause substantial damage to the forest ecosystem. In particular road construction can inflict scars on the landscape in mountainous terrain which can seldom be remedied at a later stage and only at much higher costs. In order to carry out construction and logging operations efficiently and safely, as well as in an environmentally friendly way, the following should be considered:
appropriate size and power configuration of construction and logging equipment, adjusted to the actual needs of the construction technique and harvesting system applied as well as with respect to terrain conditions;
appropriate equipment with respect to technical and safety standards, as well as ergonomic principles and requirements;
only adequately trained, skilled and experienced machine operators should be employed for road construction and timber extraction in sensitive forest ecosystems and difficult terrain;
appropriate road design fitting the road to the natural terrain as closely as possible and well planned extraction routes to facilitate road construction and timber harvesting without major problems for operators and machines as well as reduced damage to the remaining stand;
clear instruction to and close supervision of machine operators and extraction crews by supervisors responsible for road planning, construction and logging operations.
There are economic short-term advantages for the traditional forest practices carried out in Bhutan, namely road construction by bulldozer and timber harvesting by strip-wise clear-felling. The potential for medium and long-term damage to and impact on the environment, should encourage the introduction of advanced techniques throughout Bhutan and development of silvicultural techniques appropriate to moving towards environmentally sound forest practices.
In the mountainous terrain of Bhutan where forest stands not only sustain site productivity by preventing soil erosion but often protect human settlements, infrastructure and other land uses from land slides, torrents and avalanches, avoidance of site disturbance is imperative. On the other hand, active management of over-mature stands on steep slopes which are at risk of losing their commercial value as well as in some areas even more important their protective function, requires a minimum of forest access provided by forest roads.
Therefore, the implementation of environmentally friendly road construction techniques is deemed highly necessary as forest roads are unquestionably the most problematic features of timber harvesting operations from the environmental point of view. The use of hydraulic excavators in forest road construction as applied in the Kharungla road project and advanced blasting technique is considered a solution for mountainous terrain in general, but in particular for road construction in steep terrain in the Himalayan range of Bhutan.
The results of this case study show that environmentally friendly road construction as applied in the Kharungla road project is superior to road construction in the traditional way by bulldozers as applied in the Korila project from the environmental point of view. The short-term economic benefits from use of bulldozers in forest road construction in mountainous terrain are likely in the longer run to create environmental damage on a considerable scale.
A guidance for selecting the appropriate equipment for road construction in mountainous terrain taking account of side slope gradients at the construction sites is given by Gorton (1985) where the following is recommended:
|Side slope gradient||Equipment recommended|
|>70%||excavator + dump truck|
The main advantage of road construction by excavator is that balanced road construction can still be carried out on steep slopes whereas in road construction by bulldozer full bench construction techniques would have to be applied. The latter results in approximately 25–35 percent more excavated material when compared to “balanced” road construction (FAO, 1989) where cut excavation is incorporated into the layered fill built up and compacted by the excavator.
The fact that the erosion potential is directly proportional to the excavation volume and adequate compaction of the fill cannot be achieved by bulldozers (FAO, 1989), should encourage the use of excavators in road construction even in less steep terrain so that the traxcavator recommended for side slope gradients between 45 and 60 percent will be replaced by excavator rather than by bulldozer if a traxcavator is not available. The excavator is also considered the most appropriate equipment to partly compensate for the lack of other construction equipment such as a roller, grader or road scraper, which are not available now for forest road construction in most parts of Bhutan.
The traditional harvesting practice in Bhutan, strip-wise clear-felling with subsequent long-distance cable logging, can be modified towards more environmentally sound harvesting systems. The adverse environmental impacts, such as loss of biodiversity, creation of monocultures and forest with a poor species composition as well as erosion, can be reduced. This solution makes use of the available skill and equipment in the country, contributes to the livelihood of the people and improves the overall development in rural areas.
Past environmental mistakes made in accessing and managing mountainous forests in developed countries, employing bulldozers, poor blasting techniques and inappropriate silvicultural techniques should not be repeated in the natural forests of Bhutan.