Proto Andrea Rosario, PhD.

The forest industry around the world is facing common challenges in accessing wood fiber on
steep terrain. Fully mechanized harvesting systems based on specialized machines, such as
winch-assist forwarders, have been specifically developed for improving the harvesting performances
in steep grounds. While the mechanization process is recognized as a safety benefit,
the use of cables for supporting the machine traction needs a proper investigation. Only a few
studies have analyzed the cable tensile forces of winch-assist forwarders during real operations,
and none of them focused on large machines normally used in North America. Consequently,
a preliminary study focused on tensile force analysis of large winch-assist forwarders was
conducted in three sites in the interior of British Columbia during the fall of 2017.
The results report that in 86% of the cycles, the maximum working load of the cable was less
than one-third of the minimum breaking load. The tensile force analysis showed an expected
pattern of minimum tensile forces while the forwarders were traveling or unloading on the
road site and high tensile forces when operating on steep trails, loading or traveling. Further
analysis found that the maximum cycle tensile forces occurred most frequently when the
machines were moving uphill, independently of whether they were empty or loaded. While the
forwarders were operating on the trails, slope, travel direction, and distance of the machines
from the anchor resulted statistically significant and able to account for 49% of tensile force
variability. However, in the same conditions, the operator settings accounted for 77% of the
tensile force variability, suggesting the human factor as the main variable in cable tensile force
behavior during winch-assist operations.

The improvement of harvesting methodologies plays an important role in the optimization of wood production in a context of sustainable forest management. Different harvesting methods can be applied according to forest site-specific condition and the appropriate mechanization level depends on a number of factors. Therefore, efficiency and functionality of wood harvesting operations depend on several factors. The aim of this study is to analyze how the different harvesting processes affect operational costs and labor productivity in typical small-scale Italian harvesting companies. A multiple linear regression model (MLR) and artificial neural network (ANN) have been carried out to predict gross time, productivity and costs estimation in a series of qualitative and quantitative variables. The results have created a correct statistical model able to accurately estimate the technical parameters (work time and productivity) and economic parameters (costs per unit of product and per hectare) useful to the forestry entrepreneur to predict the results of the work in advance, considering only the values detectable of some characteristic elements of the worksite.

Forwarders often load logs organized in large piles by modified farm tractors, skidders, animals, other forwarders, etc., but currently, there are no studies on how the different concentrations of logs affect forwarder performance in terms of time consumption, productivity, and costs in forwarding operations. A study was conducted in three locations situated in Bulgaria (sites A and B) and in southern Italy (site C): in site A the logs were spread in the stand, in site B they were concentrated in large piles at the roadside, whereas in site C the logs were organized at the roadside in piles of medium size. The average forwarder productivity in site A obtained at an average forwarding distance of 1780 m, an average payload volume of 9.83 m3, and an average number of grips of logs with the crane grapple, during loading (22.97) and during unloading (8.97) per cycle, is 10.43 m3·PMH-1 (PMH, productive machine hour) and 9.93 m3·SMH-1 (SMH, scheduled machine hour), respectively. In site B the productivity rate was lower than that registered by the forwarder operated in site A: 9.38 m3·PMH-1 and 8.81 m3·SMH-1, respectively, at an average forwarding distance of 3760 m, average payload volume of 15.04 m3, and a mean number of grips of logs with the crane grapple, during loading and during unloading, of 23.57 and 14.10 per cycle, respectively. With regard to site C, the average machine productivitiy was 12.39 m3·PMH-1 and 11.85 m3·SMH-1, travelling a mean forwarding distance of 1630 m, transporting a mean load volume of 13.63 m3, and performing an average number of grips of logs with the crane grapple, during loading of 26.52 and during unloading of 12.36 per cycle. The ratio between the number of grips of logs with the crane grapple during loading and unloading operations in site A is on average 2.56, but in site B it is significantly smaller – mean of 1.67, due to the larger number of logs in the grapple when loading from large piles. Site C shows a loading and unloading number of grips ratio intermediate between the two Bulgarian sites. This ratio is characterized by the concentration of logs in the stand. Concentration in larger piles results in a larger volume of grappled logs by crane, and hence, lower time for loading of the forwarder and higher productivity. The obtained results show that the dispersion of small piles of logs results in a smaller volume grappled, a greater number of crane cycles and a larger loading distance, which generally, increases loading time. The larger volume of logs in the crane grapple and the shorter loading distance, when the loading operation is carried out from larger piles at the roadside, lead to less loading time. Gross costs for forwarders were 65.14 € PMH-1 at Site A, 72.96 €·PMH-1 at Site B, and 85.58 €·PMH-1 at Site C. When the forwarders were productive, the costs were 6.35 €·m-3 in site A, 7.90 €·m-3 in site B, and 6.90 €·m-3 in site C.

Ground-based forest operations can produce an intense level of soil disturbance and hamper the growth of seedlings. However, previous studies on the topic of seedling growth performance on the skid trail network showed high variability and non-uniform responses. Therefore, a multivariate meta-analysis was applied to investigate the effects of soil disturbance after ground-based forest operations on the aboveground and belowground growth of seedlings. We further assessed the effects of the following moderators: type of regeneration, type of stand, number of years since the forest operations, mass of the machine used, number of machine passes in the investigated skid trails, and the increased soil compaction in the skid trails. The results supported our hypothesis that ground-based forest operations had a greater effect on the growth of broadleaf species and natural regeneration. This was, however, mostly true for belowground growth, that was typically more affected than aboveground growth. We discovered that there is a recovery in seedling biomass and lenght following harvesting, but this is a long process that requires about ten to twenty years to begin. We found that the number of machine passes and the machine mass did not directly correspond to a higher level of impact, indicating that the actual disturbance drivers are more complicated interactions that occur among the machine, the way in which forest operations are carried out, and the soil properties. It was finally demonstrated that soil compaction was the primary cause of disturbance to seedling growth, primarily affecting belowground biomass and lenght. In particular, we identified a minimum threshold of a 30% increase in soil bulk density to observe statistically significant negative effects on seedling belowground growth. Soil compaction proved to be the main factor that can jeopardize the development of forest regeneration in the skid trails. This suggests that the same best management practices that are used to reduce soil compaction caused by machinery should also be used to reduce the detrimental effects of ground-based forest operations on seedling development. As future research directions, long-term studies are recommended to assess the recovery process dynamics. Moreover, more research on broadleaf, natural regeneration, and Cut-to-Length machinery is strongly suggested.

Ground-based forest operations can produce an intense level of soil disturbance and hamper the growth of seedlings. However, previous studies on the topic of seedling growth performance on the skid trail network showed high variability and non-uniform responses. Therefore, a multivariate meta-analysis was applied to investigate the effects of soil disturbance after ground-based forest operations on the aboveground and belowground growth of seedlings. We further assessed the effects of the following moderators: type of regeneration, type of stand, number of years since the forest operations, mass of the machine used, number of machine passes in the investigated skid trails, and the increased soil compaction in the skid trails. The results supported our hypothesis that ground-based forest operations had a greater effect on the growth of broadleaf species and natural regeneration. This was, however, mostly true for belowground growth, that was typically more affected than aboveground growth. We discovered that there is a recovery in seedling biomass and lenght following harvesting, but this is a long process that requires about ten to twenty years to begin. We found that the number of machine passes and the machine mass did not directly correspond to a higher level of impact, indicating that the actual disturbance drivers are more complicated interactions that occur among the machine, the way in which forest operations are carried out, and the soil properties. It was finally demonstrated that soil compaction was the primary cause of disturbance to seedling growth, primarily affecting belowground biomass and lenght. In particular, we identified a minimum threshold of a 30% increase in soil bulk density to observe statistically significant negative effects on seedling belowground growth. Soil compaction proved to be the main factor that can jeopardize the development of forest regeneration in the skid trails. This suggests that the same best management practices that are used to reduce soil compaction caused by machinery should also be used to reduce the detrimental effects of ground-based forest operations on seedling development. As future research directions, long-term studies are recommended to assess the recovery process dynamics. Moreover, more research on broadleaf, natural regeneration, and Cut-to-Length machinery is strongly suggested.