The cultivated poplar forests stand for a valuable source of wood for industrial and individual house-hold use, and they hold an important potential to contribute to the satisfaction of the increasing demand of lignocellulosic raw materials. They are cultivated on extended areas [1
] using fast-growing trees by operations which could be regarded as being more labor intensive compared to those specific to the traditional close-to-nature management of forests; that’s because the typical sequence includes soil preparation, planting, fertilization, irrigation, and weed control operations [3
], which are followed by regular harvesting operations such as thinning and clear-cutting [4
]. Among these, planting is crucial in the operational management because on its quality and timely implementation depends the success of new forests [5
Depending on the local forest management, terrain morphology, and the available technology, to name just few factors, planting of forests may be implemented either by mechanized [6
], partly mechanized [8
], or manual operations solely [5
]. In Romania, as well as in other Eastern European countries, partly mechanized systems are still dominating the scene of forest operations [10
]. This applies also to the planting operations of fast-growing poplar forests where the use of manual labor is still intensive. As such, at least problems in the sphere of ergonomics may arise, especially in the context in which many operations are still carried out manually around the world, and they have been proven to be physically demanding [11
]. Therefore, scientific information is still required to engineer the operations to an extent which will ensure their sustainability. This approach is congruent with recent research that describes the main pillars of sustainability in forest operations [12
], with the ergonomics and risk awareness being among them [12
]. In particular, exposure to risks of developing musculo-skeletal disorders may be one of the most critical currently-faced problems of manual work, especially in forest operations, which are developed outdoors and are generally recognized to be among the most difficult ones [14
A particular area of research in ergonomics is that referring to postural analysis which has provided important means and ways for research and improvement, enabling attempts to ensure the sustainability of various industrial sectors. As such, several methods were developed, validated, and used in time to evaluate the postural status-quo of different operations and to take corrective measures [15
]. Such approaches are of invaluable importance since the musculoskeletal disorders (MSDs) are seen nowadays to be the most common cause of severe pain and physical disability, which in turn have important negative economic effects [16
]; therefore, targeted studies have been conducted in many sectors, showing a strong relation between work factors and tasks and the development of MSDs. From these points of view, it seems that manual planting operations have received less attention by scientific research in the area of postural assessment. However, it is likely for manual planters to face awkward working postures given the tasks they are required to undertake. Such postures may refer to frequent situations in which the workers may hold their back bent and twisted, as well as to tasks requiring working with the knees bent. For instance, the Romanian standards describe working tasks that have an increased potential to generate deviant working postures in seedling planting operations [17
]. In addition, the Romanian technique of poplar planting which uses large poplar cuttings, may generate unsustainable situations from a postural point of view given the size of planting material and the ways used to handle and plant it into the pits. Both techniques have been proven to be very intensive from the point of view of cardiovascular workload [9
], and this outcome has provided some hints on the potential postural difficulties, given the fact that body posture changes are causing an increased cardiovascular activity [18
]. However, the postures themselves adopted during the work may not be the sole drivers of an increased cardiovascular workload while they could inflict other problems related to the health of workers. In our knowledge, postural assessments have not been carried out for the typical case of manual poplar planting operations.
Based on the above, the main goal of this study was to characterize, from a postural assessment point of view, the manual planting operations of poplar forests to be able to set the stage for their improvement. Two types of planting operations were selected for this study (large cutting planting and bare-root seedling planting) and the objectives were set to: (i) describing and characterizing the distribution of tasks per subjects and type of operations, (ii) describing and characterizing postural risks on subjects, tasks, and type of operations, and (iii) comparing at task and operation type level the postural risks as specific to the two planting options taken into study.
The postural risk associated with the studied manual planting operations was found to be high, irrespective of the analyzed option (CP and SP, respectively). At the task level, the effective planting (Plant) was found to generate the worst postural situation because the PRIs were estimated to be close to 300. Unfortunately, by keeping the current situation, there is little room for improvement, as the effective planting stands for the main task specific to the studied planting operations and it accounts for the greatest share in the analyzed data. Even if not presented in the results section, the dominant body postures specific to AC4, that generated the current situation, were 4141 and 4151, respectively (where the first digit—4 stands for the back bent and twisted or bent forward and sideways, 1—both arms below the shoulder level, 4 and 5—standing or squatting with both or one knee bent, respectively, while the last digit stands for force exertion less than 10 kg). These were specific to the Plant task and they accounted for 1147 and 2949 observations for CP and SP, respectively, representing 30% and 28% of the analyzed data sets. Therefore, the main problems were related rather to the back (code 4) and leg (codes 4 and 5) postures, indicating that the back was either bent and twisted or bent forward and sideways. Accordingly, the legs were found to be with one (code 4) or both (code 5) knees bent in a standing or squatting posture. These postures of the back and legs are among the most deviant according to the OWAS method, and they were imposed by the actions and motions needed to place the cuttings and seedlings into the pits as well as those needed to fill the pits and to compact the soil in them. Elucidating for these tasks are also the examples given in Figure 1
Worth mentioning that in the task breakdown, the Rest events were found to present shares of 5–24 and 4–40% for CP and SP, respectively. While these events were kept into analysis because they were related to the on-site work, and were intercalated in the typical work sequence, it is highly questionable if they could be eliminated or reduced in the general operational conditions. If so, then based on the results and task distribution presented by this study, the postural risk situation would become even worse, while the productivity will not be significantly enhanced. For instance, the total operated area (results not presented herein) in CP sites was of 0.55 ha, while in the case of SP it was of 1.46 ha. Nevertheless, these areas were operated by cohorts containing many more workers than those taken into study. Taking into consideration that the observation time was of 18 and 49 h, respectively, the global productivity could be estimated at approximately 0.03 ha per hour for both CP and SP, which was very low for the observed conditions, and it would become even lower if higher rest pauses will be taken. This situation indicates the limitations of manual work as being one of the current problems in forest operations.
Another approach which is seen as a potential ergonomic improvement is that of job rotation in the sense that work stations or tasks could be more wisely distributed between workers with the aim to reduce the postural risk. Spinelli et al. [31
] have proposed such an approach for wood debarking jobs as a measure to balance the effect of difficult work postures. Nevertheless, in the case of manual planting this approach is less useful due to the task sequence and share in the typical work, in which the effective planting will dominate irrespective of how the tasks will be redistributed among workers. In addition, the job itself is different compared to assembly lines or jobs in similar industries in which, anyway, recent work has revealed that job rotation could be less effective [33
Probably, one of the important factors that could have affected the results from an anthropometric point of view was the subjects’ body height, which varied between 165 and 185 cm. For comparison, these two body heights were found in the case of CP for S2 × L1 and S5 × L3, respectively, cases in which the Rest events also accounted for low shares (approximately 5 and 8%, respectively). As such, the PRIs for the Plant tasks were found to be of 348 (165 cm) and 255 (185 cm), respectively, indicating that lower body heights could be associated with higher postural risks. However, one may just speculate that part of these outcomes may be the results of the places at which some of the subjects have chosen to grip the cuttings with their arms when they worked to introduce them into the pits, as the arms postures coded by 2 (one arm above the shoulder level) and 3 (both arms above the shoulder level) accounted for less than 200 events in the case of CP.
A comparison with other studies helps in understanding and categorizing these kinds of operations by considering the postural risk. Studies by Marogel et al. [22
] and Cheţa et al. [29
] have addressed the problem in cultivated forests located in the same region for manual cultivation and motor-manual tree felling and processing operations, respectively. The study by Marogel et al. [22
] estimated a global PRI at 178 based on a cohort containing 14 subjects but, at the subject level, the PRI varied between 151 and 212. The operations surveyed by them were done manually by hoes, and the share of observations falling in AC4 was much lower (approximately 5%) compared to that from this study (30–35%). The study of Cheţa et al. [29
], on the other hand, estimated the PRI of motor-manual tree felling and processing at 275, which was close to other similar forest operations as described by Calvo [32
]. Therefore, it seems that operations that involve more leg movement such as those described by Marogel et al. [22
], Borz et al. [28
], as well as those that show a wider and more diverse succession of tasks [27
] present lower postural risks, which are characterized by PRIs of up to 200. In comparison, wood processing operations were characterized by different classes of PRIs which range from non-threatening situations such as those specific to wood debarking [31
], for which PRIs were found to be of up to 150, to those requiring postural improvement, such as in the case of firewood processing [30
] and sawmilling [34
], for which the PRIs were identified to be up to or even higher than 200. From this analysis, it seems that manual planting operations surveyed in this study hold an intermediary position, as they indicated PRIs of 250–259. Nevertheless, this situation requires immediate intervention for improvement, which is also supported by the statistics developed for the effective planting tasks (Plant) and by the assumption that, in other cases, the Rest events could have a lower share in the operations. Additionally, it is worth mentioning that, even if it seems to be unreasonable to find PRIs higher than 100 for Rest events, as shown by this study, and also found by other studies [27
], this situation is real in operations. In addition, comparison of jobs by considering the estimates of PRI has its own limitations because is quite difficult to infer the typical postures of body parts from which the PRIs are obtained. A better task or job comparison would have been enhanced under the assumption that all the reported studies indicate the shares per action categories, which would enable the comparison by nonparametric tests. Nevertheless, this approach doesn’t say much about the type and frequency of body part postures, which makes the analysis basis, and could be important in the work redesign effort.
Given the situation identified by this study, a good approach for improvement will be that of completely mechanizing the operations. This approach could be feasible, since some studies have shown that performance of mechanized planting reaches acceptable limits, and seedling planting machines could handle plants of different sizes [6
]. Nevertheless, for the time being, the complete mechanization of poplar planting operations could be difficult since, at least for the cutting planting, special machines need to be developed. However, machines able to handle both soil preparation and planting using the described planting material and its size need to be developed in a short time given the limited availability of work force, low productivity, poor postural conditions of manual planting operations, and the spatial characteristics of such operations (i.e., sites having areas of up to 3 hectares, widely dispersed in the territory).
In regards to the method used in this study, one could appreciate the fact that even though it is resource-intensive in data processing and analysis, a fact that has been found by the authors of this study by their experience with other studies [22
], it still provides the option of carrying on the studies by using affordable technology. While there are many other observational methods [15
], the use of OWAS has gained attention, in particular in forest operations [see the reference list], due to its ability to evaluate the whole body and the possibility to provide comparable results. However, the method produces categorical data as outputs, which is difficult to address by the estimation of some advanced postural variability and diversity metrics that could work well for data measured on continuous scales [35
]. Such approaches may be used to characterize given jobs and to better connect their postural condition to the development of MSD. They worth exploring further to see the extent to which they could be used to account for categorical data variability. Last, but not least, there is an increasing body of studies that bring evidence on less association between biomechanical postures and the development of MSDs [36
]. While the topic is still debated, further exploration is required to see if the postures adopted during the work are the sole factor causing MSDs. This is important especially in forest operations where the workers are exposed, in addition to job-related risks, to other harmful environmental and technology-related factors [14