Department of Forest and Wood Science

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Browsing Department of Forest and Wood Science by browse.metadata.advisor "Ackerman, Simon"

Now showing 1 - 6 of 6
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    An ergonomic risks assessment for manual and motor-manual pruning
    (Stellenbosch : Stellenbosch University, 2020-03) Sibiya, Zimbili Bonisiwe; Ackerman, P. A.; Ackerman, Simon; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Mechanisation and modernisation in pruning operations for South Africa's forestry industry have advanced to keep abreast with best practices internationally. Commercially planted pine species in South Africa are not self-pruning, therefore, pruning activities are done extensively to produce clear wood and for fire protection or accessibility purposes. Although traditional handheld pruning tools have been used for decades, motor-manual pruning saws have recently been introduced to South African pruning operations. This has, however, raised the question what the ergonomic risks in manual and motor-manual pruning operations potentially expose workers to. Therefore, the study aimed to assess ergonomic risks that may be associated with the manual and motor-manual pruning operations of Pinus patula stands in Kwa-Zulu Natal (KZN), Midlands at 3.5 m and 2.0 m pruning lifts. Convenience sampling of seven pruners was done to collect data on productivity (time study), workload (heart rate indices and productive heart rate), awkward postures (captured images during pruning operations) and body discomfort rating (Nordic Musculoskeletal map and the Likert scale) for ergonomic risks assessment. Statistica 64 and Excel functions were used to test for significant interactions between pruning method, pruning lift and worker and Games-Howell posthoc test for significant differences between the means of operations at a statistically significant level of 5.0 %. Awkward postures were assessed for deviation from the neutral plane of body posture. Body discomfort was analysed with Fisher’s exact test for prevalence of discomfort per recording period, frequency of discomfort rating and discomfort per body part for each pruning operation. Machine utilisation was considered the same as the duration of exposure to operation due to the nature of the operation requiring availability of operator and machine to be executed successfully. Results show that the interaction between the pruning lift, pruning method and pruner was significant for productivity, productive heart rate and body discomfort responses. Time study results showed that motor-manual (MM) operations produced the highest productivity compared to the manual (M) operations; however, the manual operations were the most efficient. Pruning operations fell under the “medium to heavy” workload classification with mean heart rates at work of 115, 113, 110 and 119 beats per min (beats.min-1), for 2.0 m M, 2.0 m MM, 3.5 m M and 3.5 m MM respectively. Common postures adopted by workers were the shoulder and elbow abduction and extension, twisting and neck extension, ulnar deviation and bending of the back. High prevalence of discomfort was reported for manual (55 %) operations compared to MM (49 %) and 2.0 m pruning lift (61 %) and 3.5 m pruning lift (42 %). Pruning operations were rated as severe discomfort except for 3.5 m MM, which was rated as moderate discomfort. Some of the postures adopted by workers must be adjusted to avoid future health problems, such as high flexion of the back in the 2.0 m M and MM operations with a high prevalence of discomfort reported. Additionally, the duration of exposure to the operation and the repetitive nature of pruning operations are additional ergonomic risks identified in this study. These results show promise as the first steps in investigating the effect of M and MM operations on Ergonomic and productivity of operations. However, it is recommended for this study to be repeated with a larger sample and with gender as an additional factor because that is much more thorough representation of the current pruning operation teams. Additionally, a thorough focus on musculoskeletal disorder since many workers have been in the field for several years.
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    Evaluation of a mechanized CTL harvesting system in different geometric thinning operations in terms of productivity, cost, biomass conversion, residual stand damage and spacing uniformity
    (Stellenbosch : Stellenbosch University, 2021-12) Makoto, Munyaradzi; Talbot, Bruce; Ackerman, Simon; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: This study was aimed at comparing conventional 7th row thinning with diagonal thinning in terms of productivity, cost, biomass conversion efficiency, residual stand damage and spacing uniformity. The study was based on two adjacent Pinus patula compartments on the Mpumalanga Highveld. A time study was conducted to test time consumption and productivity of both harvesting and forwarding between the two treatments. Residual tree damages were assessed by inspecting all individual trees within research plots for any woundings. Cost calculations were carried out on each machine per thinning treatment to determine which machine was more cost-effective. Voronoi polygons and simulations were used to determine spacing uniformity and biomass conversion efficiency was tested by enumerating woody residues that were above the commercial limit diameter remaining in the stand after timber extraction. iii Summary This study was aimed at comparing conventional 7th row thinning with diagonal thinning in terms of productivity, cost, biomass conversion efficiency, residual stand damage and spacing uniformity. The study was based on two adjacent Pinus patula compartments on the Mpumalanga Highveld. A time study was conducted to test time consumption and productivity of both harvesting and forwarding between the two treatments. Residual tree damages were assessed by inspecting all individual trees within research plots for any woundings. Cost calculations were carried out on each machine per thinning treatment to determine which machine was more cost-effective. Voronoi polygons and simulations were used to determine spacing uniformity and biomass conversion efficiency was tested by enumerating woody residues that were above the commercial limit diameter remaining in the stand after timber extraction. Harvesting results showed a significant difference between the two treatments at (p < 0.05). Conventional 7th row thinning had the highest mean productivity at 16.49 m3/PMH compared to 14.36 m3/PMH for diagonal thinning. Forwarding results also showed a significant difference between the two treatments at (p < 0.05). Diagonal thinning had a mean productivity of 4.61 m3/PMH compared to 5.36 m3/PMH for the conventional 7th row thinning. The conventional 7th row thinning method had the lowest cost of R273.93/ m3 compared to R324.28/ m3 for diagonal thinning. Residual tree damages showed a significant difference between the two treatments at (p < 0.05). Diagonal thinning had an average residual tree damage of 8.9% compared to 4.4%. The diagonal thinning method had the highest fibre losses at 12.65 m3/ha and 10.52 m3/ha for conventional 7th row thinning. There was a significant difference between the two treatments. The study showed that conventional 7th row thinning is a better method in terms of productivity, cost and residual tree damages. Diagonal thinning, however, proved to be better in terms of thinning quality with regards to improving spacing uniformity and improving size distributions.
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    Quantifying financial returns from commercial forestry research trials in the Zululand Region of KwaZulu-Natal
    (Stellenbosch : Stellenbosch University, 2018-03) Seboa, Dannyboy; Ham, Cori; Ackerman, Simon; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: South African plantation production is depended on a limited land resource. This limitation in land drives the goal of increasing production from the same land area. There is however a growing necessity for the justification of additional investments made towards intensive forest management practices. Thus, intensive forest management practices should maximize production yields at a reduced cost per hectare. This study investigated site-specific financial returns of research field trials conducted at the ICFR. These trials included: (i) Site-Potential focusing on site specific fertiliser recommendations (FR), (ii) Forest management focusing on residue management (RM), vegetation and coppice management (VCM) and Eucalyptus regeneration (ER). According to the ICFR, these are the relevant research areas to address key challenges facing the South African forestry industry. The studied research trials where located in the Zululand region of KwaZulu-Natal. The region predominantly consists of Eucalyptus grandis, Eucalyptus grandis hybrids and other Eucalyptus species. The area is further considered to be highly productive for Eucalyptus grandis hybrids and clones. Reported research findings were collected using a Meta-analyses Framework as an extractive tool. Thereafter, financial returns were determined using generic discounted cash-flow (DCF) models, which was followed by a sensitivity analyses to test results from the DCF models. Due to insufficient information presented from the Meta-analyses framework for ER research trials a cost comparison study was initiated on them. The results from this study showed financial returns in FR research trials ranging from R49 201 and R273 524 ha-1 based on Land Expectation Values (LEVs) and 10 to 29% in Internal Rate of Returns (IRRs), the financial gains did differ per site. However, for mid-rotation FR research trials there were no financial gains. Financial returns for RM research trials declined through successive rotations, this could possibly be caused by soil compaction and the specific residue management techniques. Lastly, the financial returns for VCM research trials (vegetation management) and coppice management research trial returns were highly depended on cost-effective coppice reduction techniques. Based on the results, the generic DCF model developed was successful in quantifying site-specific financial returns of three (FR, RM and VCM) of the four studied research fields.
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    Skills development of mechanised softwood sawtimber cut-to-length harvester operators
    (Stellenbosch : Stellenbosch University, 2018-03) Wenhold, Roland Marius; Ackerman, P. A.; Ackerman, Simon; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: In this study, a South African pine sawtimber mechanised cut-to-length harvesting operation – comprising felling, debarking, debranching and cross cutting of log assortments – was analysed using .stm-files from StanForD software. The objective of the analysis was to describe and model productivity development learning curves of beginner harvester operators in both clear-felling and thinning operations. A cohort of trainee operators were selected based on the results of a comprehensive battery of psychometric tests that assessed their aptitude for the complex array of decision-making required of harvester operators. These trainees subsequently completed several sequential tests on a harvester simulator. Following the simulator training, operators commenced with work on machines (harvesters) themselves until they were considered capable of working unsupervised. Within the framework of this progression of operator selection, simulator training and in-field operations, it was possible to model a potential learning curve of a typical beginner harvester operator in softwood sawtimber in both clear-felling and thinning operations. With regards to simulator training, the results of this study show that, on average, a trainee operator will start at a performance level (PL) of 60% lower than the population’s performance level (PPL) and end with a PL of 24% higher than the PPL. Furthermore, when the PL of an average simulator trainee was measured over a period of 9.2 days or 27 tests (three tests per day), it was evident that his PL improved with 269% following the efficient simulator training. Once in-field, thinning operators worked with an average tree size of 0.18m3 where they started at a productivity of 13.71 m3 ·PMH-1 (cubic meter per productive machine hour) at month one and managed to increase their productivity to 38.96 m3 ·PMH-1 (overall average = 28.8 m3 ·PMH-1 ) at the end of month 12. Clear-felling operators’ felling productivity level on an average tree volume of 0.54m3 started at 27.5 m3 ·PMH-1 in month one and increased to 43.75 m3 ·PMH-1 (overall average = 41.9 m3 ·PMH-1 ) at the end of month 12. Finally, on average, a thinning operator can reach the end of the learning phase after nine months. The two clear-fell operators reached the end of their learning curve after five and eight months respectively. On average, thinning operators increased their performances by 218%, while clear-fell operators increased theirs by 104%. These findings suggest acceptable learning periods and performance increases for beginner harvester operators.
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    Understanding the system and supply chain effects of two residue management treatments in pine and eucalyptus plantations
    (Stellenbosch : Stellenbosch University, 2022-03) Mahadeo, Leeshan; Talbot, Bruce; Ackerman, Simon; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: There is an increased interest in understanding the effect of different residue management practices on forestry in South Africa. In addition to clearly established environmental benefits of residue mulching, as opposed to burning residues in-situ, as mulching or mastication offers the alternative of comminuting these residues almost immediately after harvesting. The aim of this study was to investigate the cost of mulching and determine whether this cost is justified through potential savings from increased pitting and planting productivity in the forestry value chain. Relevant data was collected from sites in Zululand and Bulwer in KwaZulu-Natal and Jessievale on the Mpumalanga Highveld. The study was limited to Eucalyptus grandis x urophylla pulpwood and Pinus patula pulpwood and sawtimber regimes. The study included estimating residual biomass and remaining stump volumes using a Zigzag and Line-Intercept methods respectively. Time studies quantified time consumption and the productivities of the various mulching machines, mechanised pitters, semi-mechanised planters, manual pitters, and manual planters, between treatments. An attempt to classify mulch quality was investigated. The costs of each operation per residue treatment were calculated to determine cost effectiveness. Initial plant growth response to mulched and burnt residues were evaluated. Mulching results for pulpwood residues showed no significant difference between Eucalyptus sites (0.35 ha) and pine sites (0.36 ha PMH-1) and were also not affected by residual biomass volume. Significant differences were found in Eucalyptus mechanised pitting productivity between mulched (0.26 ha PMH-1) and burnt (0.25 ha PMH-1) treatments. Mechanised pitting on sawtimber pine stands differed significantly with a 24% increase in productivity after mulching. Productivities of 0.57 ha PMH-1 and 0.46 ha PMH-1 on mulched and burnt pine sawtimber residues respectively were seen. Manual pitting was more productive for burnt sites (0.06 ha PPH-1) than mulched sites (0.05 ha PMH-1). Semi-mechanised planting was 27% faster on mulched sites (1.70 ha·PMH-1) than on burnt sites (1.33 ha PMH-1). Manual pine planting after mulching was 33% faster compared to planting on burnt sites. This resulted in a manual planting productivity on mulched sites of 0.08 ha PPTH-1 being greater than on sites where residues were burnt (0.06 ha PPTH-1). In both pine and eucalypts, increases in productivities in mechanised pitting, semi-mechanised planting, and manual planting (except manual pitting) after mulching were evident. The total cost of mulching was approximately R 5 450 ha-1 for eucalyptus sites and R 6 170 ha-1 in pine pulpwood sites. The increase in pitting and planting productivity after mulching approximately offsets the mulching cost by R 220 ha-1 on eucalyptus and R 290 ha-1 in pine pulpwood. These saving in increase productivity after mulching are however not enough to justify the expense of mulching generally. When considering mulching foresters should holistic approach the undertaking by considering the biological advantages of mulching in general including soil nutrients benefit as well as long term growth and yield gains, in addition to the increase in productivity of pitting and planting after mulching.
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    Unlocking the potential of harvester on-board-computer data in the South African forestry value chain
    (Stellenbosch : Stellenbosch University, 2019-12) Terblanche, Marius; Ackerman, P. A.; Ackerman, Simon; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: The South African forest industry is in a state of change from motor-manual to fully mechanised harvesting systems. This is predominately driven by health and safety concerns related to motor-manual harvesting systems, and the need to enhance systems productivity and product quality.Through the use of technologically advanced harvesting machinery with on-board computing systems, and standardised and compatible data collection software, all mechanised processing operations are able to produce real-time (time-stamped) data related to almost every action or function of the machine. The software referred to above is the Standard for Forest Communication (StanForD) first developed by Skogforsk in 1987, as a standard for managing the information flow from the forest machines through the value chain.Although most machines in South Africa are compatible with the StanForD systems, the usefulness of the concept remains under-utilised due to limited understanding of the interface between harvester heads and the computing systems. This includes validating the integrity and accuracy of the data emanating from the system, and that is firmly embedded in quality assurance and computer calibration. The objective of this study is to propose and develop an applicable bark deduction method for Pinuspatula in the Mpumalanga Highveld region of South Africa for more precise log volume calculations. This was accomplished by modelling historical P. patulabark thickness data from the Mpumalanga Highveld region to obtain bark thickness estimates for the two methods of bark deduction to be assessed that are available on the Ponsse Opti OBC system. Three trials were run: T1 (status quo no bark deduction function), T2 (length-based [LB] bark deduction method) and T3 (diameter-class length-based [DLB] bark deduction method). The two bark deduction methods were implemented successfully, and the harvester`s under bark (UB) diameter measurements compared well with manual measured UB diameter measurements which was derived through the novel application of photogrammetry technology. Results showed that if no bark deduction method is used the harvester over-estimates stem volume by 13.7% and 14.6% for each of two respective bark deduction methods. Furthermore, by the nature of P. patula bark being extremely thick at the base of the tree stem, means this over-estimation is even greater for butt logs. The harvester over-iv estimated the log volume of the first plywood log cut by 20.8% for T1, where through the implementation of a bark deduction method the volume estimation was improved to an under-estimation of only 1.6% and 0.2% for T2 and T3 respectively. The results of this study show that by not implementing bark deduction methods the harvester`s log volume estimations are grossly over-estimated and the usefulness of theharvester`s data for value chain management is lost.