Grapple cable yarding: a productivity model for fast-growing tree plantations in Sarawak, Malaysia

Today, the two most important tasks faced by harvesting foresters and contractors are selecting the equipment and systems best suited to the site, and then to use this equipment in the best way possible (MacDonald, 1999). Experts estimate that the importance of tree plantations will continue to grow and that by 2050 75 per cent of the global fibre supply will be sourced from dedicated plantations (Ragauskas et al., 2006). To meet this growing demand plantations will most likely expand to steep slopes due to the priority given to agricultural and urban development, on flat land. New technological advancements in both cable yarding and ground-based harvesting systems has to a certain extent provided forest engineers with more options to choose from. Whether considering these options individually or in combination, they will have to make good choices in order to realise the full potential of forest plantations. One of the most promising techniques consist of an excavator-based unguyed yarder equipped with a new radio-controlled grapple carriage, fed by another excavator stationed on the cut-over. This system is very productive, avoids in-stand traffic and removes operators from positions of high risk. This long-term study was conducted on 12 different teams equipped with the new technology, operating in the fast-growing Acacia mangium plantations of Sarawak, Malaysia. Data were collected continuously for almost 8 months and represented 555 shifts, or over 55,000 yarding cycles - each recorded individually. This large data pool allowed for the development of robust models for system production, utilization and availability estimated respectively at: 63 m3 per productive machine hour (excluding all delays), 63 per cent and 93 per cent. The study also determined the effects of yarder type and team competence on productivity and utilization. Regression analysis of experimental data yielded a strong productivity forecast model that was highly significant, which accounted for 50 per cent of the total variability in the dataset and was validated with a non-significant error estimated at less than 1 per cent. The models reported in this study are especially robust, because they were obtained from a long-term study that covered multiple teams and accumulated an exceptionally large number of observations. While gained specifically on one yarder make (Alpine Yarder) and a specific plantation type (Acacia mangium), the information in this study can be extended to other similar machines and plantations, because the sheer volume of data allows cautious generalization. The teachings of kaizen, which suggest small-step work improvements, was adopted in order to propose the process of possible improvements, by combining elements of other harvesting systems as shown in Figure 1 below (Vorn Industries, 2017). Forestry is essentially a problem of transportation (Schenck, 1911) and the efficiency of such a transportation system will ultimately be determined by technology developments which drive system productivity (Ger & Klvac, 2014). Therefore, when we talk about systems for the future we should view them not as predictions or as prescriptions but as options that may be selected or rejected (Wood, 1979)