The effect of forest management systems on productivity and costs of cable yarding operations in southern China

Abstract

The extension of plantations in the southern provinces of China was supposed to fill the demand-and-supply-gap within the country’s forest products industry. But a factor strongly limiting the supply capacity is the low productivity of the conventional manual clearcut systems currently in use. In addition, a political shift in silvicultural objectives towards multiple-use and continuous cover plantation forestry is not coherent with such operations. Therefore, new operation systems with low impact technologies - such as cable yarding - are needed to increase productivity while incorporating other management goals. An elemental time study, following the snap back timing method, was conducted with a cable yarding crew operating a mobile tower yarder in two comparable pine (Pinus massoniana Lamb.) stands adjacent to Pingxiang, located in subtropical southern China. Two different management systems were analyzed: a clearcut with full-tree extraction on the first and a selective cut operation with stem-length extraction on the second site. Based on the results of the time study, the yarding performances within the two management systems were evaluated by calculating productivity and associated costs. The gross operational system productivity for extraction at the clearcut, namely 9.9 m³/SSH_Operation (scheduled system hour) and 9.30 €/m³, was nearly twice as high at half the costs as the selective cut, which reached 5.1 m³/SSH_Operationand 18.86 €/m³. Full-tree extraction led to shorter cycle times and higher load sizes, essentially resulting in higher mean productivity per cycle. One of the main shortcomings of the selective cut operation was the significantly longer lateral extraction distances, which led to longer cycle times and delays, such as hang ups. However, when comparing the systems under standardized conditions, the clearcut only had a 15.2 % advantage in performance over the selective cut and both operations bear the potential to increase their productivity e.g. through better log presentation during the felling operation. Although extraction productivity at the clearcut site exceeded the one from the selective cut, the ecological consequences of this operational system with full-tree extraction with respect to erosion and nutrient depletion are uncertain and could add to the long-term overall forest management costs. Selective cuts also have the potential to generate larger tree dimensions, and thus more valuable timber that can potentially fetch higher market prices, which could compensate for the higher costs of operation. However, uncertainties regarding the future development of operational regulations make it difficult to draw an overall conclusion for best practices.

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