Review Reports - Economic Assessment Comparison Between Battery- and Petrol-Powered Chainsaws: Performance in Conifer Forest Operations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study compares the operational performance and economic costs of battery-powered and petrol-powered chainsaws. The topic is relevant, and the field data are valuable. However, several aspects of the economic analysis, statistical methods, and interpretation of results require clarification and revision.

(Major comments)

Economic analysis: Please clarify the assumptions and calculations used for battery lifespan, replacement frequency, the number of batteries and chargers required, and annual working days. The methodology for the 24-year cost comparison should be presented transparently.
Cost reduction percentages: The statement that petrol-powered chainsaws have costs approximately 84% higher than battery-powered chainsaws does not agree with the reported values. Please check the calculations and clearly define the reference value used to calculate the percentage difference.
Statistical analysis: Please justify the use of fuel type as a random effect in the mixed-effects model. The model should also account for potential dependence among observations collected using the same chainsaw or operator, where appropriate.
Estimation of daily energy and fuel consumption: The daily consumption estimates appear to rely on assumptions and time-use proportions from a previous study rather than direct measurements over full working days. Please clarify the estimation procedure and acknowledge its limitations.
Study design and conclusions: The number of trees reported in the Methods section does not agree with the number reported in the Results. Please resolve this discrepancy. In addition, clarify how operator differences were addressed and avoid generalizing the findings beyond the three chainsaw models and two forest conditions investigated.

(Minor comments)

Correct “Comparation” to “Comparison” in the title.
Correct the definition of “PetS” in the list of abbreviations.
Check the consistency of numerical values and percentage calculations between the text and tables.
Review the manuscript for English language and grammatical errors.

Author Response

Economic analysis: Please clarify the assumptions and calculations used for battery lifespan, replacement frequency, the number of batteries and chargers required, and annual working days. The methodology for the 24-year cost comparison should be presented transparently.

ANSWER Thanks for the valuable comment. The useful lifetime of the batteries was estimated at approximately 12 and 8 years for BatS and BatM, respectively. These values were obtained by dividing 2,500 and 1,700 charging cycles by 200 annual working days, assuming that each battery is charged once per working day.

The number of batteries was estimated by extrapolating the results from the time study to a full working day, using chainsaw utilization rates reported in previous studies that examined these proportions in greater detail. The number of chargers corresponds to the quantity required to fully charge all batteries each day.

The assumption of 200 annual working days was based on an approximation that considered weekends, public holidays, and the fire season restrictions typical of Mediterranean regions.

The 24-year cost horizon was selected because it is the least common multiple of 12, 8, and 1. This methodology allows investments with different time horizons to be compared on an equivalent basis. For battery-powered chainsaws, the main investment cost is associated with battery replacements, whereas for petrol-powered chainsaws the primary investment is the chainsaw itself.

Cost reduction percentages: The statement that petrol-powered chainsaws have costs approximately 84% higher than battery-powered chainsaws does not agree with the reported values. Please check the calculations and clearly define the reference value used to calculate the percentage difference.

ANSWER We thank the reviewer for identifying this issue. We agree that the original presentation of the percentage difference did not clearly specify the reference value used in the calculation. Our intention was to express that the battery-powered chainsaws had substantially lower energy costs than the petrol-powered chainsaw. Using the petrol-powered chainsaw cost (7.35 €/tree) as the reference, the battery-powered chainsaws (1.15-1.19 €/tree) incurred approximately 84% lower energy costs per felled and processed tree. The text has been revised accordingly to clearly define the reference value and avoid any ambiguity.

Statistical analysis: Please justify the use of fuel type as a random effect in the mixed-effects model. The model should also account for potential dependence among observations collected using the same chainsaw or operator, where appropriate.

ANSWER Thank you for this valuable comment. Following you suggestion, we reconsidered the random-effects structure of the model. Fuel type was initially specified as a random effect; however, after further evaluation, we concluded that fuel type represents the main treatment factor of interest in this study. The objective of the analysis was to quantify and explain differences in harvesting costs between battery-powered and petrol-powered chainsaws rather than variability among individual chainsaws or operators. Therefore, fuel type was considered more appropriately modelled as a fixed effect.

We also considered the potential dependence among observations collected using the same chainsaw or operator. However, the study included only a limited number of chainsaws and operators, providing insufficient levels for the reliable estimation of additional random effects. Under these conditions, variance components associated with chainsaw or operator identity cannot be robustly estimated, and any inference based on such random effects would be limited.

Consequently, the model was reformulated with fuel type as a fixed effect, allowing direct estimation and interpretation of cost differences between battery-powered and petrol-powered chainsaws, which constitutes the main objective of this analysis.

Estimation of daily energy and fuel consumption: The daily consumption estimates appear to rely on assumptions and time-use proportions from a previous study rather than direct measurements over full working days. Please clarify the estimation procedure and acknowledge its limitations.

ANSWER On the one hand, the present study was designed to compare the three chainsaws under the same workload, with the same number of trees, DBH, stem volume, and felling conditions. This would be difficult to achieve in a longer-term test.

On the other hand, in a short-term test it is difficult to capture the variability of situations that ultimately determines the proportion of useful chainsaw operating time. However, the chainsaw utilization rates used in this study were obtained from previous studies that investigated these aspects in greater detail.

This limitation is explained throughout the paper, especially in the Discussion section, so that readers are aware of it.

Study design and conclusions: The number of trees reported in the Methods section does not agree with the number reported in the Results. Please resolve this discrepancy. In addition, clarify how operator differences were addressed and avoid generalizing the findings beyond the three chainsaw models and two forest conditions investigated.

ANSWER Thanks for identifying this mistake. Originally, the plan was to fell 15 non-commercial trees, but during the tests, due to constrains in accessing comparable trees, we reduced this number to 14. And we forgot to update it in the material and method section.

As regarding the operators, the test was conducted by four operators with similar experience. In the Advanced Forest, the test was performed by three operators, each felling and processing four trees using two different chainsaws. In the Juvenile Forest, one operator was replaced by another, and the same methodology was followed. Each operator felled and processed five commercial trees and seven non-commercial trees using two different chainsaws. To balance the experimental design, each operator used the chainsaw that had not been used in the Advanced Forest.

We omitted this explanation in the text as we consider that explaining all these details in depth could be somewhat confusing for the reader and would considerably extend the Materials and Methods section without providing substantial additional information for the interpretation of the results.

(Minor comments)

Correct “Comparation” to “Comparison” in the title.

ANSWER Done

Correct the definition of “PetS” in the list of abbreviations.

ANSWER Done

Check the consistency of numerical values and percentage calculations between the text and tables.

ANSWER Done

Review the manuscript for English language and grammatical errors.

ANSWER Done

Reviewer 2 Report

Comments and Suggestions for Authors

Overall, this manuscript is interesting and well structured. However, I have some concerns and requests for clarification detailed below:

Table 1, BatM uses a full-chisel chain, whereas the other models use half-chisel chains. How did authors ensure this difference did not bias the test results? Does chain type affect felling productivity? In addition, BatM also has the lowest maximum chain speed and the heaviest weight among the three models. Do these factors influence the results to any extent?
In table 2, authors stated the initial equipment cost, but what about ongoing operating and maintenance costs (e.g., chain oil, 2-stroke lubricant, routine maintenance)? These costs likely differ across chainsaw types and could impact the economic analysis.
Line 137, please clarify how many trainers from the local forestry school were involved in testing. Did a single trainer operate all three chainsaws (allowing for direct comparison), or did different trainers test different chainsaws? If case of different person operate different chainsaw, it might be effect to the performance of using chainsaw.
Figure 1, the scale and text in Figure 1 are too small to read clearly. Please increase the axis label sizes.
Table 5, shows that BatM resulted in the highest CPT. What factors do authors believe drove this result (e.g., chain type or other specifications)? Furthermore, please expand on the trend observed between AF and JF, although AF resulted in a lower CPT than JF, it required higher fuel consumption, making the overall AF operation more expensive.
Before reaching final conclusions, did authors account for battery life and replacement costs over some years? Including battery degradation/replacement would likely alter the long-term comparison against petrol chainsaws.

Besides, please maintain a consistent presentation order for equipment across all tables. Table 1 authors used BatS, PetS, BatM, whereas Tables 4 and 5 use BatS, BatM, PetS.
Similar in Table 4, authors wrote "Juvenile" and "Advanced", whereas in Table 5, "Juvenile (JF)" and "Advanced (AF)", and in Table 6, only "JF" and "AF". Please pick one format and apply it consistently throughout the manuscript. In addition, Table 4 lists JF before AF, whereas Table 6 lists AF before JF. Please standardize the order across all tables, in order to avoid confusion the readers.

Author Response

Table 1, BatM uses a full-chisel chain, whereas the other models use half-chisel chains. How did authors ensure this difference did not bias the test results? Does chain type affect felling productivity? In addition, BatM also has the lowest maximum chain speed and the heaviest weight among the three models. Do these factors influence the results to any extent?

ANSWER Thanks for the valuable remark. Before starting the tests, we observed that the BatM had a lower chain speed and was equipped with a different chain type. Although we considered replacing it with a half-chisel chain, we decided to retain the original factory setup. In fact, the chain type may have partially compensated for the lower chain speed, thereby reducing potential performance differences between machines.

Moreover, any increase in productivity or fuel consumption associated with a full-chisel chain is expected to be relative low to the effect of machine weight, as discussed in the final paragraph of the Discussion section.

In table 2, authors stated the initial equipment cost, but what about ongoing operating and maintenance costs (e.g., chain oil, 2-stroke lubricant, routine maintenance)? These costs likely differ across chainsaw types and could impact the economic analysis.

ANSWER We acknowledge that operating and maintenance costs may differ among chainsaw types. However, this was a short-term study focused on operational performance, and a detailed assessment of these costs was beyond its scope. Furthermore, maintenance costs represent a very specific cost component that is difficult to quantify accurately in a short-term experiment because they depend on several factors, including machine utilization and maintenance practices. Although electric-powered chainsaws do not require some of the maintenance associated with 2-stroke engines, there is limited information available in the literature to support a robust economic comparison under comparable operating conditions.

Line 137, please clarify how many trainers from the local forestry school were involved in testing. Did a single trainer operate all three chainsaws (allowing for direct comparison), or did different trainers test different chainsaws? If case of different person operate different chainsaw, it might be effect to the performance of using chainsaw.

ANSWER The test was conducted by four operators with similar experience. In the Advanced Forest, the test was performed by three operators, each felling and processing four trees using two different chainsaws. In the Juvenile Forest, one operator was replaced by another, and the same methodology was followed. Each operator felled and processed five commercial trees and seven non-commercial trees using two different chainsaws. To balance the experimental design, each operator used the chainsaw that had not been used by them in the Advanced Forest.

We consider that explaining all these details in depth could be somewhat confusing for the reader and would considerably extend the Materials and Methods section without providing substantial additional information for the interpretation of the results.

Figure 1, the scale and text in Figure 1 are too small to read clearly. Please increase the axis label sizes.

ANSWER Done

Table 5, shows that BatM resulted in the highest CPT. What factors do authors believe drove this result (e.g., chain type or other specifications)? Furthermore, please expand on the trend observed between AF and JF, although AF resulted in a lower CPT than JF, it required higher fuel consumption, making the overall AF operation more expensive.

ANSWER The main difference between BatM and the other chainsaws was its weight, which was almost twice as high. This made it more difficult for the operator to handle, resulting in an increase in test time in both forest types.

AF consisted of fewer trees, which resulted in a lower test time, whereas the larger average tree size resulted in higher energy consumption. As shown by the model, larger trees were associated with higher energy consumption and operating costs.

Before reaching final conclusions, did authors account for battery life and replacement costs over some years? Including battery degradation/replacement would likely alter the long-term comparison against petrol chainsaws.

ANSWER Yes, we considered the values claimed by each manufacturer in terms of guaranteed charging cycles per battery The useful lifetime of the batteries was estimated at approximately 12 and 8 years for BatS and BatM, respectively. These values were obtained by dividing 2,500 and 1,700 charging cycles by 200 annual working days, assuming that each battery is charged once per working day.

Besides, please maintain a consistent presentation order for equipment across all tables. Table 1 authors used BatS, PetS, BatM, whereas Tables 4 and 5 use BatS, BatM, PetS.

ANSWER thanks for the observation, the tables have been revised accordingly

Similar in Table 4, authors wrote "Juvenile" and "Advanced", whereas in Table 5, "Juvenile (JF)" and "Advanced (AF)", and in Table 6, only "JF" and "AF". Please pick one format and apply it consistently throughout the manuscript. In addition, Table 4 lists JF before AF, whereas Table 6 lists AF before JF. Please standardize the order across all tables, in order to avoid confusion the readers.