A portable sawmill, called Wokabout Somil in Melanesian Pidgin, was studied in Papua New Guinea during May and June 1990. The purpose of the case study was to measure and analyze the productivity, recovery rate and sawn timber quality of the sawmill in order to increase possibilities for reducing waste and improving round timber usage in commercial logging operations in PNG.
Technical data concerning the sawmill were collected during a field test at the Kui logging operation, about 120 km south of Lae. Ten sample logs were sawn and the time consumed and recovery data were recorded. It was found that the roundwood consumption of the sawmill per hour varies between 0.5 and 2.5 m3/h on working time. If the transport and moving times of each log are included, the size of the log is a critical factor in determining productivity. On effective time basis it can be assumed that the length of the log has a significant effect on the productivity of the sawmill. The recovery rate was found to vary between 45 % and 56 %. The recovery rate of a Wokabout Somil depends considerably on the sawing pattern used. The sawn timber production per day was found to vary between 1.0 m3/day and 2.0 m3/day depending on the skills of the sawmilling crew.
The quality of the sawn timber from the sawmill in this study was found to be rather good. In general the quality of the products depends a lot on the level of skills of the sawmilling crew in sawdoctoring and sawmilling itself. With a well trained sawmilling crew and good skills on sawdoctoring the Wokabout Somil is able to produce construction timber fulfilling the grading rules for construction timber in PNG.
The cost of the sawmill was found to be 181.5 K/m3 (about US$ 191/m3) during the first year of operation. As an average the yearly expenses of the sawmilling operation are about 19 000 K based on a yearly production of 104 m3/year.
The roundwood sources that exist within the commercial logging operations were studied from earlier logging studies and by interviewing personnel of the Forestry Department. It was determined from the logging studies made in PNG that there exist after commercial logging operations about 60 m3/ha merchantable sized standing mature trees on the logging site. According to the Forestry Department there are also left as an average 30 m3/ha of uncommercial mature trees on the logging site.
Volume of the trees damaged during logging operations and left in the forest was found to be about 15 m3/ha in size classes from 20 to 50 cm BHD.
The amount of waste logs extracted from the forest but left in the export harbour for not fulfilling the export grading rules was found to be from 10 to 35 % of the exported amount depending on the species selection of the logging operations.
As a result of the study it was concluded that mobile sawmilling in PNG could be enhanced by combining it with commercial logging operations. The logging companies have a significant amount of reject logs that are not accepted to be exported and thus need to be processed in the forest or at the export harbour. These reject logs can be used as raw material for local mobile sawmillers. The stand in logged over areas also gives sawmillers a possibility to do salvage logging in them. When doing these salvage loggings the sawmillers have a big advantage of the roads that were built in the forest during the previous logging operations. Combining mobile sawmilling in PNG with controlled logging would have a positive impact on forest management of the country.
The combination of logging operations and mobile sawmilling benefits the involvement of local people in the use of their own forest resourses.