A comparative study of the influence that motor-manual felling and mechanised felling has on stem breakage.

Abstract

Motor-manual felling has been the predominate method of severing trees in the felling process of a forest harvesting operation. Yet this method has been coupled with numerous injuries and deaths, as trees can strike fallers during this task. An alternative felling method was developed in the form of mechanised tree felling, in an attempt to reduce the frequency of injuries. Subsequently, mechanised felling is poorly understood when compared to motor-manual felling upon the impact it has on stem breakage.

183 trees were assessed by measuring the frequency of breakage, height of the first break and the volume retention abilities of three felling treatments; motor-manual, mechanised felling out of the stand and mechanised felling into the stand. The effect that directional felling had upon the length to the first break was also investigated for motor-manual and mechanised felling out of the stand.

The percentage of stems that broke once felled was 73%, 76% and 94% for motor-manual, mechanised out of the stand and mechanised into the stand felling respectively. The height at which the first break occurred for the aforementioned felling treatments was 71%, 71% and 69% of the total tree height. Mechanised felling out of the stand had the greatest volume retention ability with 94.5% of the trees total volume being below the first break. Followed by 93.7% for motor-manual and 91.9% for mechanised felling into the stand, however these differences were statistically insignificant (p=0.14). Lastly the length to the first break for motor-manual and mechanised felling out of the stand failed to statistically change when a tree was felled through a range of directions from downhill to uphill.

The influence that motor-manual felling and mechanised felling out of the stand had on stem breakage is similar, yet mechanised felling into the stand had a much greater impact on the percentage of stems that broke. With further improvements in technology, it could be seen that the number of mechanised tree-felling operations over take motor-manual felling, as their impact on stem breakage is comparable.