Faculty of AgriSciences

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The Faculty of AgriSciences at Stellenbosch University (SU) is held in high esteem at national and international levels for the quality of its training and research and also as consultant in the agricultural and forestry industry.

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Analysis of a mechanised cut-to-lenth harvesting operation through use of discrete-event simulation
(Stellenbosch : Stellenbosch University, 2015-03) Rabie, John Frederick; Ackerman, P. A.; Pulkki, Reino Evert; Laengin, Dirk Werner; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Abstract Mechanised timber harvesting operations are rapidly increasing in South Africa, particularly in Eucalyptus pulpwood production. There are however still considerable inefficiencies in implementation and evidence of unnecessary operational variability in current mechanised systems. A typical South African cut-to-length operation for harvesting Eucalyptus pulp logs utilising two excavator-based harvesters and one purpose-built forwarder was studied. The ability of performing discrete-event simulation using R was tested. One of the harvesters and the forwarder were simulated individually and alternative work methods were modelled and compared against the original work method. The changes in productivity based on productive machine hours and cost were recorded. The input data was negatively affected by the large variation in stand and individual tree characteristics. This led to a decrease in model validity. Machine simulation models where however able to capture trends found by other authors. The current method of felling a combination of the four and five tree wide swaths yielded the highest productivity of 11.43 m3 hr -1. Tree size had a notable effect on both the harvester and forwarder productivity. Increasing the tree size from 0.14 m3 to 0.20 m3 and 0.3 m3 led to productivity increases of 5.26 m3 hr -1 and 13.14 m3 hr -1, respectively. When comparing the original mean stack sizes of 2.5 m3, stacks with a mean volume of 5.4 m3 yielded an increase in productivity of 5.91 m3 hr -1. Fitting a larger grapple (1 m2 vs. original 0.8 m2 opening) to the forwarder showed increased productivities across all stack sizes. Forwarder productivity decreased by up to 17.8% with an increase in extraction distance. The largest decrease in forwarder productivity was noted when increasing the on-road travel (both loaded and unloaded) distance from 0 m to 100 m (single road scenario); decreasing by 6.1% when using the standard grapple and 7.6% when using the larger grapple. When using both roads the largest productivity decreases were found when increasing the on-road extraction distance from 0 m to 200 m; decreasing by 15.3% when using the standard grapple and 17.8% when using the larger grapple. Costing of each individual machine was carried out per alternative scenario. Decreases in harvester cost were noted between increasing tree sizes, and forwarder cost increased with extraction distance. Harvester cost decreased by as much as R35.24 m-3 when increasing mean tree volume from 0.14 m3 to 0.3 m3, whereas forwarding cost decreased by a maximum of R1.13 m-3 when extracting larger stacks (5.4 m3), when compared to the observed system (2.5 m3 stacks). Removal of all road travel elements and piling directly at roadside, showed savings of up to R10.21 m-3 when compared to the observed system. R proved to be useful for carrying out discrete-event simulations, however, dedicated simulation probability distributions need to be developed before it can be said that R is highly suitable for discrete-event simulation.
Analysis of the market structures and systems for indigenous fruit trees: the case for Uapaca Kirkiana in Zambia
(Stellenbosch : University of Stellenbosch, 2009-03) Moombe, Kaala Bweembelo; Ham, Cori; Clark, Jeannette; Franzel, Steve; Ackerman, P. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
This study is about marketing of Uapaca kirkiana fruit in Zambia, a fruit that has great economic value especially among the rural and urban poor. It contributes to general food security. In southern Africa, farmers and other stakeholders have identified Uapaca as a priority species for domestication. Current agroforestry initiatives are promoting integration of indigenous trees into farming systems to provide marketable products for income generation. Domestication of trees however, depends on expanding the market demand for tree products. There is considerable evidence that expanding market opportunities is critical for the success of domestication innovations but farmers have been introduced to domestication with little consideration for marketing. The existing market potential can be achieved through sound knowledge on markets and marketing. Information on the marketing of Uapaca fruit is inadequate. This study, therefore, aimed at generating information on the marketing of Uapaca kirkiana fruit, including the basic conditions of demand and supply of the fruit. The main study was conducted in Chipata and Ndola districts in the Eastern and Copperbelt provinces respectively, while fruit pricing was conducted in Lusaka district in Lusaka Province. Questionnaires and participatory research methods were used to collect the data. A total of 37 markets involving 49 collectors, 59 retailers, 189 consumers and 20 government forest workers are included in the study. The study reveals that there is demand for the fresh and secondary products of the fruit and hence substantial fruit trading exists in Zambia. However, the marketing system is characterised by underdevelopment. There is insufficient capacity to satisfy the demand for the fruit and institutional /policy support to Uapaca fruit market expansion. Currently, only basic technology for product development exists. The results suggest a need to address policy and capacity development for expansion of Uapaca kirkiana fruit industry. To improve the Uapaca trade industry, the study proposes developing and scaling up policy strategies, fruit processing sector, research-extension-trader-agribusiness linkages, infrastructure development and knowledge generation for improved understanding of the Uapaca fruit markets.
Biomass modelling of selected drought tolerant Eucalypt species in South Africa
(Stellenbosch : Stellenbosch University, 2013-12) Phiri, Darius; Seifert, Thomas; Ackerman, P. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forestry and Wood Science.
ENGLISH ABSTRACT: The study aims at developing models for predicting aboveground biomass for selected drought tolerant Eucalyptus (E) species (E. cladocalyx, E. gomphocephala and E. grandis x camaldulensis) from the dry west coast. Biomass models were fit for each of the species and a cross-species model was parameterised based on pooled data for all the three species. Data was based on destructive sampling of 28 eucalypt trees which were 20 years of age and additional five five-year old E. gomphocephala trees. Preliminary measurements on diameter at breast height (dbh), height (h) and crown height were recorded in the field. The sampled trees were then felled and samples of discs, branches and foliage were collected. Density of the wood discs and the bark was determined by a water displacement method and computer tomography scanning (CT-scanner). Stem biomass was reconstructed using Smalian’s formula for volume determination and the calculated densities. Upscaling of the crown was carried out by regression equations formulated by employing the sampled branches. Further assessment was carried out on a sub-sample by subjecting the samples to different drying temperatures in a series between 60 and 105ºC. Linear models were parameterised by a simultaneous regression approach based on Seemingly Unrelated Regression (SUR) using the “Systemfit” R statistical package. The predictor variables employed in the study were dbh, d2h and h in which the coefficient of determination (R2), Mean Standard Error (MSE) and Root Mean Standard Error (RMSE) were used to determine the goodness of fit for the models. Akaike Information Criteria (AIC) was also used in the selection of the best fitting model. A system of equations consisting of five models was formulated for each Eucalyptus species. The biomass prediction models had degrees of determination (R2) ranging from 0.65 to 0.98 in which dbh and d2h were the main predictor variable while h improved the model fit. The total biomass models were the best fitting models in most cases while foliage biomass had the least good fit when compared to other models. When the samples were subjected to different drying temperatures, stem wood had the largest percentage change of 6% when drying from 60ºC to 105ºC while foliage had the lowest percentage change of less than 2%.
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.
Harvesting of invasive woody vegetation (Eucalyptus lehmanii, Leptospermum laevigatum, Acacia cyclops) as energy feedstock in the Cape Agulhas Plain of South Africa
(Stellenbosch : Stellenbosch University, 2011-12) Kitenge, Emile Museu; Ackerman, P. A.; Seifert, Thomas; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: This study is aimed at testing the possibility of using woody biomass from three invasive woody vegetation types (Spider Gum, Myrtle and Acacia) for production of bioenergy in the Cape Agulhas Plain. Physical recoverability of the woody biomass was studied by means of a semi-mechanized harvesting system to evaluate potential productivity, operational costs and the estimated yield energy gain. The system consisted of five components: manual harvesting, motor-manual harvesting, extraction, chipping and road transport. Data on the system productivity was obtained using activity sampling and time study techniques. Activity sampling was applied on manual and motor-manual harvesting in order to record harvesting time and standard time study techniques were used to obtain time data for extraction, chipping and road transport operations. Findings revealed benefits associated with the utilisation of invasive woody vegetation as energy feedstock. Therefore, the problem of exotic tree species can be dealt with by transforming them into energy feedstock, thus minimising the effect of invasive plants. At the same time essential biomass energy can be produced, while some of the cost of production could be offset by the benefits accruing from the biomass energy. The Acacia site, characterized by larger mature dense trees, had the highest amount of harvested biomass compared to the rest of the vegetation types (i.e. Myrtle and Spider Gum). The overall system productivity was found to be significantly influenced by a low equipment utilisation rate, estimated at 50%. This resulted in low production rates in general. The low supply rate of material to the chipper by the three-wheeled loader (1.5 – 5.3 oven-dry tonne per production machine hour) was found to be a major constraint in the chipping process, especially when considering that the chipper is potentially capable of chipping 4 – 9.4 ODT PMH-1 at the harvesting sites. This resulted in a significant energy balance of 463 GJ between output and input energy of the system. The overall total supply chain system costs based various road transport distances of species ranged from R 322.77 ODT-1 to R 689.76 ODT-1 with an average of R 509 ODT-1. This was found to be costly compare to the case where high machine utilisation rate and optimal productivity are used (average of R 410 ODT-1), biomass recoverability in this field trial had a higher total system cost due to low productivity, resulting from the low equipment utilisation rate applied.
Impact of harvesting machinery on soil physical parameters : evaluation of ProFor model in three main forestry regions of South Africa
(Stellenbosch : University of Stellenbosch, 2007-12) Kachamba, Daud Jones; Ackerman, P. A.; Rozanov, Andrei Borisovich; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
Timber harvesting operations in plantation forestry in South Africa are rapidly being mechanised. However, movement of forest machines over the soil increases the potential for soil compaction and disturbance. In an effort to prevent forest soil damage, the Technical University of Munich developed the “ProFor” software. This software enables the calculation of critical soil water content for a given machine and physical soil characteristics. The applicability of ProFor in the South African forestry industry was assessed through the comparison of the evaluation of the impact of forest harvesting machines on soil properties with ProFor predictions. The study was conducted in four harvesting sites located in three of the major plantation forestry regions of South Africa namely: KwaZulu-Natal; Eastern Cape and the Western Cape. The impact of forest harvesting machines on soil physical properties was assessed through the evaluation of changes in soil saturation, soil bulk density and rut depth. The impacts of machine movements on soil physical properties were then compared with ProFor’s predictions. The study has indicated that ProFor gave good predictions of the critical water contents for most of the studied soils except for sandy soils. The study has also indicated that in more than 75% of the observed cases (r = 0.76) ProFor gave valid predictions of rut formation. However, ProFor predictions poorly correlated (r = -0.1) with the observed soil compaction. The model can be adopted for the South African forestry industry for use in the management of wet spots of a plantation. However, ProFor can be of even greater importance if a separate algorithm was built to be used for the prediction of soil compaction which is a common hazard in most South African forestry.
The impact of mechanical log surface damage on fibre loss and chip quality when processing Eucalyptus pulpwood using a single-grip harvester
(Stellenbosch : Stellenbosch University, 2014-03) Van der Merwe, Jaco-Pierre; Pulkki, R. E.; Ackerman, P. A.; Langin, D.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Mechanised harvesting operations are growing in popularity in South Africa, as motor-manual and manual harvesting operations pose significant health and safety risks to workers. Potential damage inflicted by single grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking eucalypts, may affect fibre recovery and chip quality. Chip quality is important as it influences pulp quality and recovery in the kraft pulping process. The study investigated the influence of two mechanised debarking treatments in eucalypts (three feed roller passes and five feed roller passes along the stem surface) with feed roller induced log surface damage on chip uniformity, size, purity and wood fibre loss. The two mechanised treatments were compared against chips produced from manually debarked logs. In addition, the effect of two log drying periods (one week and two weeks) and three log sections (base, middle and top logs) on chip quality were also analysed. An economic evaluation was conducted to quantify potential recoverable pulp value losses associated with debarking treatments and log drying periods. Logs subject to manual debarking produced significantly less undesired sized chips than both three pass and five pass mechanically debarked logs. Potential recoverable pulp revenue for chips produced from five pass and three pass mechanically debarked logs were valued at R 60.54 BDt-1 and R 50.90 BDt-1 less than wood chips produced from manually debarked logs. Two week dried logs produced significantly less under-sized chips than chips produced from one week dried logs. However, two week dried logs produced wood chips with significantly more over-thick chips than logs dried for one week. The volume of undesirable sized chips produced during chipping increased with decreasing log size. Potential recoverable pulp revenue for chips produced from one week dried logs were valued at R 137.90 BDt-1 less than chips produced from two week dried logs. Manually debarked logs produced chips with significantly less bark content than three pass mechanically debarked logs (0.008 % vs 0.062 %). Five pass mechanically debarked logs produced chips with significantly less bark content than three pass mechanically debarked logs (0.018 % vs 0.062 %). Middle logs also produced chips with significantly less bark content than base logs (0.016 % vs 0.056 %). Top logs produced chips with significant less bark content than base logs (0.017 % vs 0.056 %). In all cases the bark content was considerably less than the maximum of 1.0 % generally specified by kraft pulp mills. Both three pass and five pass mechanically debarked trees caused significant fibre losses of 2.6 m3 ha-1 and 5.1 m3 ha-1 respectively. Wood fibre losses in terms of total extractable wood volume for three and five pass mechanically debarked trees were 0.8 % and 1.6 % respectively.
Multi-stem mechanised harvesting operation analysis : application of discrete-event simulation
(Stellenbosch : University of Stellenbosch, 2009-03) Hogg, Glynn A.; Pulkki, Reino E.; Ackerman, P. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
In this study, a multi-stem harvesting operation was observed and time studies carried out on its machines. A stump-to-mill simulation model (System 1) of this system was subsequently built using a commercial simulation software package (Arena 9) and data from the time studies were incorporated into the model. Following this, another two stump-to-mill multistem models (Systems 2 and 3) were built using the same simulation software package and parameterised input data. These two models represented hypothetical systems which were tested against System 1 and against one another in terms of machine balance within the system, production rate and cost. System 2 used identical equipment to System 1, but practised alternative operating methods. Some of System 3’s machines and operating methods differed from those in Systems 1 and 2. The objectives of the study were to: 1. Determine whether or not commercial simulation software can be used to adequately model forest harvesting operations. 2. Gauge potential system balance, production and/or cost improvement/s achievable through application of simulation-based operation adjustments. 3. Define beneficial equipment operation and application practises for multi-stem systems. 4. Through construction and use of the commercial software package in producing forest harvesting operation models, evaluate the software’s usability in terms of its applicability to and ease of use in such models, as well as its ability to meet forestrybased user requirements.
Pattern and dynamics of remnant dry afromontane forests : a case study in Northwestern Ethiopia
(Stellenbosch : Stellenbosch University, 2019-03) Wale, Haile Adamu; Geldenhuys, Coert J.; Ackerman, P. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Often forest managers get confronted with the management of a new forest area for which no information is available. The concept of this dissertation is to use a combination of common analytical tools to develop a first approximation of the ecological status of Afromontane forests in northwest Ethiopia. This included analyses of the floristic-structural composition and species associations of these forests, their plant-plant and plant-site relationships, and their response to different disturbance factors. These aspects form the basis for developing a sustainable resource use management system. The floral composition, plant-plant and plant-environment interactions, spatial scales of disturbance affecting regeneration of species differently, and population status of species, were investigated in three Afromontane forests of northwest Ethiopia, to develop a first approximation of the ecological status of forests. A systematic sampling design in homogenous stands was employed to collect vegetation and environmental data. Data were collected from 150 nested circular plots, with 50 plots sampled in each of three Afromontane forests, namely Alem Saga, Gelawudiwos and Tara Gedam. Each plot consisted of a main plot of 100 m2 and a sub-plot of 1 m2 , respectively for the woody and herbaceous species. Soil and litter were collected from the subplot. Topographical variables, including altitude, aspect and slope, were collected from each plot. Species were grouped into four propagule types, based on the type and size of the part of the fruit or seed or combination of the two, that gets dispersed by dispersal agents: fleshy large, fleshy small, dry large and dry small. Propagules considered as small when <5 mm diameter, and large with ≥5 mm diameter. Diversity and diversity profiles were analysed, using Shannon index and Renyi index, respectively. The floral similarity with other Afromontane forests in Ethiopia and Africa, and woodlands from Ethiopia, were analysed, using Sørensen similarity index. TWINSPAN and DCA analyses (indirect gradient analysis) were used separately for woody and herbaceous species to identify plant communities. Direct gradient analysis (CCA) was used to investigate the relationship between the identified communities and various environmental variables. Spatial ordination analysis, using DCA, was used as an analytical approach to investigate the scales of disturbance (gap sizes), affecting the regeneration of canopy tree species. The population structure of selected tree species was analysed using stem diameter class distributions across different communities. A total of 209 vascular plant species, including 109 woody and 100 herbaceous species, were recorded. Seven of these species were known to be endemic to Ethiopia. The species presented 58% with dry and 42% with fleshy propagules, with 40% small, dry propagules. In herbaceous species, dry and small propagules were predominated with 64%. The area showed a Shannon-Weiner diversity and evenness value of 4.0 and 0.26, respectively; indicating that the study area has high floristic diversity despite uneven distribution of the individuals among the encountered species. The three most diverse Afromontane forests, with their shared number of species and Sørensen similarity percentages between brackets, within the present study area, were Wondo Genet with 80 (35.6 %), Gendo with 70 (37.1%) and Denkoro with 68 (35.5%), but 23 species (6.6%) were shared with the Southern Cape in South Africa at the southern end of Africa. The Metema woodlands contributed a 20.6% similarity for herbaceous species. Such floral similarity of Afromontane forests maybe attributed to fragmentation of their historical landmass connectivity (vicariance) and dispersal between more local forests. Four main woody plant communities along with sixteen sub-communities and two main herbaceous plant communities along with eight subcommunities were identified. Different communities showed different affinities towards different gradients, despite some overlap occurring among communities. Radiation index (calculated from slope and aspect) and altitude were found to be the common highly significant environmental variables to explain the occurrence and composition of both herbaceous and woody communities. Various scales of disturbance affected regeneration of canopy tree species across forest communities, ranging from fine to coarse spatial scales. Some species, including Prunus africana, Olea capensis subsp. macrocarpa, Olea europaea subsp. cuspidata and Schefflera abyssinica showed critically poor regeneration, which need conservation attention. Plant communities were also characterized by different gradients and spatial scales of disturbance affecting their regeneration, indicating the need for different management interventions. The information obtained in this study, about floristicstructural composition, species associations, their plant-plant and plant-site relationships, and their response to different disturbance factors, provide the essential basis for guiding better resource use management of these forests.
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.
Slope effect on costs and productivity of single-grip purpose-built and excavator based harvesters
(Stellenbosch : Stellenbosch University, 2016-12) Martin, Chad Jay; Ackerman, P. A.; Laengin, Dirk; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: In this study a mechanised Eucalyptus pulpwood cut-to-length harvesting operation comprising felling, debarking, debranching and cross cutting of assortments, was observed using time studies to determine the effect of slope on harvester productivity and cost of wood production. Time studies and data analysis was done according to the South African Forestry time study standard and machine costs according to the South African Harvesting and Transport Costing Model. Two different types of harvesting machines were studied; an excavator based machine, Volvo EC210BF, and a purpose built levelling machine, TimberPro TL725B, both fitted with Maskiner SP 591 LX harvester heads. A single operator with significant experience and training on both machines was used throughout the duration of the study. The machines were observed harvesting on a range of slopes, from level to 50% in two separate work corridors with relatively similar trees in terms of individual tree volume and form. The species studied was a Eucalyptus grandis x camaldulensis clone. Continuous slope data, as opposed to slope categories, for each position at which the harvesters would position themselves to undertake harvesting and processing, was derived using large footprint LiDAR data of the area. The purpose built harvester was levelling enabled as opposed to the Volvo which was not. Apart from differences in mass, the Volvo was not modified for forestry work and the booms were on different sides of the particular machine. Cost calculations were carried out on each machine to determine which machine was more cost effective. The study design was a 2 x 2 factorial design with two treatments (machine type) against slope and individual tree volume as factors. The results indicate that the productivity of the excavator based machine decreased by 0.048m3.PMH-1 for every 1% increase in slope. The purpose built machine was not significantly affected by slope in this study and maintained an average productivity regardless of extreme slope. The purposed built machine was found to have a higher mean productivity (16.24 m3.PMH-1) than the excavator based machine (13.00 m3.PMH-1), but this extra productivity came at a price, as the excavator based machine was more economical per cubic metre. The mean harvest cost for the purpose built machine was found to be R122.67.m-3 whilst the excavator based machine achieved a mean cost of R94.46.m-3.
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.
The use of time study, method study and GPS tracking in improving operational harvest planning in terms of system productivity and costs
(Stellenbosch : University of Stellenbosch, 2010-12) Odhiambo, Benedict O.; Ackerman, P. A.; Pulkki, R. E.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: This study aims to quantify the benefits of implementing an operational harvesting plan in forest harvesting operations. This is to be achieved by comparing productivity and costs from unplanned and planned harvesting operations. The study was conducted on a Pinus radiata plantation owned by Mountain to Ocean Forestry Company (Pty) Ltd (MTO) located near the town of Grabouw in the Western Cape Province of South Africa. MTO conducts harvesting operations using semi-mechanised tree-length harvesting systems. A wheeled H67 Clark Ranger cable skidder is used to extract tree-lengths from infield to the landing. Data was obtained both manually (work study) and from GPS tracking. Choking and dechoking data was obtained through time and method studies. GPS tracking was used to measure travel loaded and travel empty times, as well as travel distances and travel speeds. The aim of using both manual techniques and GPS tracking was to obtain detailed and spatially accurate information about the operation. The operating costs were estimated using South African Harvesting and Transport Costing Model. Productivity of the newly introduced tagline system (45.97 m³/pmh) exceeded that of mainline system (37.85 m³/pmhh) by 26%. The unit production cost of using tagline system (R20.21/m³) was 10% lower than the unit production cost of using mainline system (R22.54/³3). There were no benefits to be gained from improving the level of skid trail construction by removal of logging residue or cutting down stumps to as near the ground level as possible. A combination of manual (time and method studies) data collection and GPS tracking provided more detailed and accurate information on the semi-mechanised harvesting system.

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