Time and cost of thinning "natural" rejuvenations on calamity surfaces with the Husqvarna FBX-535 device ("spacer")
After the storm "Kyrill" (January 2007), numerous forestry enterprises in North Rhine-Westphalia left the devastated areas for "succession" to natural, unguided regeneration. Depending on the pre-rejuvenation, which has partly survived the storm, these areas will be overgrown with 5 to 12-year-old trees in the 2013 growing season, with softwoods dominating by far. On three intensively surveyed experimental areas of the department, an average of more than 13,000 trees per hectare with heights of over 0.5 m, whose diameter at this level fluctuated between 0.2 and 23 cm - and this with a height range of up to 14 m. Figures 1 and 2 give an impression of the holdings as of May 2013.
Figure 1: The View into a succession area
Thinning out such stands was largely overdue in summer 2013; many trees were already too thick for the use of "classic" brush cutters (with the circular saw blade as a separating tool). The forestry training centre for forestry work and forestry technology, Arnsberg-Neheim, regarded the use of the Husqvarna FBX 535 brush cutter as a sawing unit as a solution for alternative motor manual processing.
Figure 2: The oldest and highest trees of the time study
Fig. 3 shows the machine, now commonly referred to as a "spacer": next to the drive unit, a boom is mounted in a frame carried on the operator's back. The torque of the motor is transmitted to a chain saw set via a flexible, then rigid drive shaft. The real novelty of the spacer is that the (rigid) part of the drive shaft to be manipulated is held by an elastic band at the end of the boom, and this leads to a significant relief of static holding activities of the arm and shoulder muscles.
Figure 3: Husqvarna FBX-535 "Spacer", work photo
With the chain saw unit of the spacer, the cutting diameters of the trees in refining operations (unlike with the classic brush cutter) no longer represent the limiting factor. The disadvantage is that the remaining floor protrudes from the ground relatively pointed and high (21 cm in the average of our experiment): access and traffic on the surfaces thinned out by spacers remain problematic for several years.
It is difficult to estimate area productivity (e.g. in hours per hectare) using previously known franking rates. This was the reason for an extensive time study carried out by the Arnsberg Education Centre and the ifa in June/July 2013 for the "Spacer Alternative". The evaluations resulted in a model that allows the estimation of the time requirement per hectare with a statistical certainty of around 70 %.
The model has been integrated into an (EXCEL) spreadsheet that can be called as a separate file called SPACER.xls. It is structured in the same way as the following table in this document. The three influencing variables that the model shows for productivity can be seen in the cells with a yellow background: their amounts must be noted in the green fields for a succession area that is due for thinning. The resulting planned time appears in the first line highlighted in red. This planned time exceeds the pure working time (RAZ) recorded in the study by a factor of 1.3 (130 % efficiency). The share of general times taken into account in the model refers to these RAZ. If you consider it appropriate, you can change this proportion in the corresponding table line; this is not recommended.
It is difficult to estimate area productivity (e.g. in hours per hectare) using previously known franking rates. This was the reason for an extensive time study carried out by the Arnsberg Education Centre and the ifa in June/July 2013 for the "Spacer Alternative". The evaluations resulted in a model that allows the estimation of the time requirement per hectare with a statistical certainty of around 70 %.
The model has been integrated into an (EXCEL) spreadsheet that can be called as a separate file called SPACER.xls. It is structured in the same way as the following table in this document. The three influencing variables that the model shows for productivity can be seen in the cells with a yellow background: their amounts must be noted in the green fields for a succession area that is due for thinning. The resulting planned time appears in the first line highlighted in red. This planned time exceeds the pure working time (RAZ) recorded in the study by a factor of 1.3 (130 % efficiency). The share of general times taken into account in the model refers to these RAZ. If you consider it appropriate, you can change this proportion in the corresponding table line; this is not recommended.
Figure 4: Calculation example
It is also possible to subjectively adjust the hourly earnings of the worker and the share of non-wage labour costs in the grey cells. The resulting personnel costs per hectare for operational purification appear in the second line highlighted in red.
The performance-relevant parameters "diameter of remaining stand" (at 50 cm plant height) and "number of trees to be removed" should be determined on a representative sample area of 100 m²; this corresponds, for example, to a circle with a radius of 5.6 m. It is recommended to instruct the worker intensively in the surroundings of this area and to check the quality of work later.
The direct procedural costs must also take into account the operation of the spacer. Depending on the fuel/lubricant mixture (for the two-stroke engine), these machine costs will range between 8 and 11 euros per hour of operation for around 60% of the previously reported planned time (2013).
The detailed description of the test design and details for evaluation can be found in ifa's A series 10.
The performance-relevant parameters "diameter of remaining stand" (at 50 cm plant height) and "number of trees to be removed" should be determined on a representative sample area of 100 m²; this corresponds, for example, to a circle with a radius of 5.6 m. It is recommended to instruct the worker intensively in the surroundings of this area and to check the quality of work later.
The direct procedural costs must also take into account the operation of the spacer. Depending on the fuel/lubricant mixture (for the two-stroke engine), these machine costs will range between 8 and 11 euros per hour of operation for around 60% of the previously reported planned time (2013).
The detailed description of the test design and details for evaluation can be found in ifa's A series 10.