Sensitivity analysis of an optimal access road location in hillyforest area: a GIS approach

American Journal of Applied Sciences, Dec, 2008 by Mohd Hasmadi I., J.C. Taylor

INTRODUCTION

There are various models for establishing the efficient forest road alignment and evaluating optimum density of forest roads network for the transport of timber commodity through a combined use of tractor and truck. Most of them are based on the calculation of common timber transport costs and costs for forest roads. A few studies describe a model based on economic evaluation of alternative roads (1). Conducted a road study that identified the broad feasibility of accessible corridors. They identified and selected broad corridors which were used for detailed evaluation of optimum road potential. Further analyses were supported by aerial photo interpretation, field survey and DEM analysis. Other models were applied to allocate potential roads, which might best minimize environmental impact. This evaluation is done by calculating a minimum total score from variable factors related to conservation of forest land and based on constraints and topographical features (2), (3). In natural dipterocarp forest like Malaysia, timber volume per ha are scattered over a large area. Extraction by tractors to the main logyard is slow, in every shift only a small number of logs is extracted and so costs are rather high. Transport by trucks is much quicker, a big quantity of logs is transported at the same time, so this method of transport is cheaper. Therefore, the denser the forest roads network, the higher are the costs incurred for the roads construction and the impact to the environmental is greater. This is the reason why the surface area and the distance of the road are used to determine the optimum road alignment and density of forest roads. In order to acquire an ideal environmental protection in hill forest the effort should be made to avoid any sensitive site such as excessive slope, elevation, hydrological buffer zone, etc. If not possible to ovoid these sites, an effort must be made to minimize impact to the forest ecosystem.

The road design and construction process is the most expensive and time consuming portion of a harvest operations plan. It is not surprising that so many road design tools and optimization models have been built to assist the development of transportation plans. Part of the design process is to evaluate a sufficient number of alternative routes to locate a final optimal access that meets operational and environmental targets. In fact, the problem of choosing the optimum forest road alignment forest is important in theory but in practice it is difficult to solve. However, it observes that modeling through mathematical programming and information contained within geographical information system (GIS) is useful to overcome the problem. Therefore the objective of this work is to describe an attempt to compute the optimal allocation of forest road corridor in hilly area of Peninsular Malaysia using GIS approach and sensitivity analysis to satisfy the result

MATERIALS AND METHODS

Description of the study area: The technique is demonstrated with a forest management compartment of Sungai Tekai Forest Reserve of Pahang State, Peninsular Malaysia. The demonstration site consists of several compartments covers an area about 5758.32 ha (Fig. 1). It is situated within latitude 04[degrees]C10'N-04[degrees]C30'N, and longitude 103[degrees]C03'E-103[degrees]C30'E, about 240 km north-east of the capital Kuala Lumpur. The elevation is mostly over 600 m above sea level. The slope gradient of the study area is undulating with steep rugged slopes ranging from 100 to 800. The annual precipitation is about 210 cm with a high tropical climate with mean temperatures ranging from 20-31[degrees]C. Based on the north-east Pahang Schematic Reconnaisance Soil Map of 1965 (4) the principle soils occurring in this area are from the Munchong-Serdang Series (Order Oxisol-Ultisol), Tropeptic Haplorthox-Typic Paleudult, Orthic Feralsol-Dystric Nitosol). The texture of the soil ranges from silty loam to clay loam.

[FIGURE 1 OMITTED]

Definition used for forest road system and application: Several classifications and road systems can be found in literature. In different country a different classification and system were used. The (5) categorised forest road by three categories such as haul road (includes primary or main road, secondary road and feeder road), skid trail and access road. For the purpose of this study, the modification of definition and designing a classification system for forest road was based on the existing classification system by Malaysian Forestry Headquarters, Kuala Lumpur and road classification for tropical high forest (6). It can be noted that, according to this classification the roads constructed within Sungai Tekai Forest Reserve area, especially at the selected study compartments were classified as secondary roads and was defined as temporary and may be semi-permanent, connective lines from secondary log yard to primary log yard of primary forest road, used by winch lorry and accessible by truck only under dry conditions, road width carriage way including shoulders is about 8 m. road have a simpler standard of construction and are usable by a truck only under favourable weather condition, road surface is partially unpaved and seriously compacted.