Productivity, efficiency and costs of manual saw and electric shear pruning operations in Pinus elliottii stands of Mpumalanga, South Africa

ABSTRACT

Timber pruning mechanization has received little attention in South Africa. The objective of this study was to compare the productivity, efficiency and the costs of using manual saws and electric shears in low pruning operations. The study was conducted in Pinus elliottii forest stands in Mpumalanga, South Africa. Manual saw and electric shear pruning treatments were used in 2 m pruning lifts. A work study approach using a factorial experiment in an unbalanced randomized block design environment was used in this study. A total of 656 pruning cycles were observed for manual saw and 852 for electric shear pruning. Stepwise and subsets regression analyses were applied to enable best subsets selection using the R² adj. and Mallow’s Cp criteria. Multiple regression analyses were used to determine pruning time and productivity. Mean manual saw pruning productivity (426 trees day⁻¹) was a function of number of branches and branch thickness while mean electric shear pruning productivity (447 trees day⁻¹) was estimated by the number of branches, branch thickness, tree height, and ground slope. Generally, the observed mean values were higher than predicted ones for both treatments and productivity of manual saws was 4.7% lesser than that of electric shears. Equipment performance was not significantly (t = 0.57; p > 0.05) different between treatments. The cost tree⁻¹ for shears was US$.01 higher than that for manual saws. In essence, manual saws were equally cost effective with plausible pruning quality gains. Future studies should focus more on the economics of pruning mechanization in timber plantations.

KEYWORDS:

• Average worker
• centiminutes
• ergonomic
• knot-free wood
• pruning lift
• time study

Acknowledgements

We are indebted to SAFCOL for providing space, time and financial resources to carry out this study. We are also grateful to the Editorial Team and two anonymous reviewers for their revision and improvement of this paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the South African Forestry Company Limited (SAFCOL).