Motor-manual versus mechanised operations - which is better for thinning in pine plantations?

The site impacts, including residual tree damage, of two harvesting systems were evaluated and compared.

The thinning operation involved the removal of between 36 and 39% of the trees in young umbrella pine (Pinus pinea) plantations. With the motor-manual operations, trees were felled with chainsaws and skidded to landing using an agricultural tractor fitted with the necessary extraction attachments. The mechanised system consisted of a feller buncher and grapple skidder. The weights of the tractor, feller buncher and grapple skidder were 4, 22 and 10 tons respectively. The residual stand damage, the occurrence and severity of soil compaction, and the effect of soil compaction on soil biological activity was determined.

Under the conditions encountered, the results showed that the motor-manual operations damaged 5% of remaining trees, while the mechanised system only damaged 1.5%. The wounds created by the mechanised systems were also four times smaller than those of the motor-manual system. This was due to the better and more controlled handling of trees. Soil compaction increased by 3% after the tractor extracted, and by 6% after the feller buncher and grapple skidder. However, the feller buncher consistently selected larger trees than the motor-manual operators, and removed more tons per hectare. Also, because the initial bulk density of the soil was lower for the mechanised system versus the motor-manual system, the larger increase in soil compaction was expected. Therefore, there was no significant difference between the soil compaction increases of both systems. CO2 levels in the soil increased due to the machine activities, but there was no difference between the two systems. Therefore the mechanised system could be used as it caused no additional site impacts compared to the motor-manual system and resulted in less residual stand damage.

This research was published in the Biosystems Engineering Journal, Vol. 113 (2012). The authors were N Magagnotti, R Spinelli, O Guldner and J Erler. Source: http://www.sciencedirect.com/science/journal/15375110/113/2