Synthetic forest-road network can locate high and low standard forest roads at the same time, and reduce forest road construction and maintenance costs. It can also reduce hauling and operational costs, thus maximizing the revenue and efficiency from timber harvesting. This study developed an approach to lay out synthetic forest-road network and evaluated the approach by applying it to a field site and comparing the results with an existing forest road network.
A synthetic forest-road network was laid out for 5,957 ha of forestland in Pyeongchang-gun, Gangwon-do using ArcGIS program. First I determined landing and operational points, and then connected these points considering hauling cost that was based on timber volume and topography. The developed road network was further categorized into main and spur roads depending on the desired density of a synthetic forest-road network.
The study results are as follows.
1. I investigated landing size and operation space based on literature review on case studies and field survey, focusing on turn-around area and curved area of ridge top and valley. The results showed that most of the available space was about 100 ㎡. Also, the current study suggested a minimum landing size of 300 m2 and operation space of 200 ㎡, considering amount of operation work and equipment size. Application of these suggested numbers increased 144 individual sites with 102,033 ㎡ area and 722 individual sites with 1,157,120 ㎡ area for 5% and 20% slopes.
2. I found that the optimum road density was 18.6 m/ha; main road, 5.9 m/ha; and working road, 12.6 m/ha that was 2.2 times the main road density. These numbers were less than the values from 2008 study, which was due to the increase in forest road construction cost and maintenance cost that was added to calculating the density of a synthetic forest-road network.
3. The current study provided an approach for synthetic forest-road network using ArcGIS program. A thematic maps was generated using topography and forest stand maps. Then, cost surface was generated using TPI model, slope steepness, and stand volume. Also, landing and operational points that satisfied constraints were identified and connected using minimum cost route and selecting forest road class, thus presenting a synthetic forest-road network.
4. To evaluate the synthetic forest-road network that was applied to the field site, I compared and analyzed the effects of 7 different road-networks: (A) no road assumed, (B) existing forest-road network, (C) synthetic forest-road network, (D) main forest-road network, (E) working forest-road network with the same road density as the synthetic forest-road network, (F) main forest-road network, (G) working forest-road network with the optimal road density. The analysis results showed that the synthetic forest-road network (C) resulted in the best indices to evaluate the forest-road network such as average and standard deviation of hauling distance, development index, and Winding coefficient of forest road. Also, main forest-road network with the optimal road density worked (F) best for potential hauling area; and working forest-road network with the same road density as the synthetic forest-road network(D), for Timber volume available for skidding. The difference between them and the synthetic forest-road network (C) was small, especially compared to forest road construction cost; therefore, the synthetic forest-road network (C) was considered best for cost-efficacy.