Masters Degrees (Forest and Wood Science)
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- ItemA practical framework to forecast wood prices for timberland appraisals(Stellenbosch : Stellenbosch University, 2024-03) De Villiers, Peter Charl; Ham, Cori; Talbot, Bruce; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: The study investigates a practical framework for price forecasting when estimating the fair market value of a forestry asset. Understanding the environment in which appraisals are conducted is important as the practice is regulated by different financial reporting and valuation standards. This extends to forecasting revenues when determining the expectation value of an asset. While these standards do not prescribe price forecasting, it provides a useful framework to ensure that the price forecasting technique used by appraisers are consistent with the principles of fair value accounting. This includes consideration of how market participants price assets. Price forecasting from the perspective of appraisal practice can be seen as a more distinct genre of forecasting, focused more on longer term price trends than trying to capture short term periodicity. This also reflects the long-term nature of forestry investments. A useful source of information on price forecasting is from financial statements of listed companies and from surveys. Secondary survey data in particular was useful in determining the methods most favoured by appraisers. The results show that a surprisingly large number of appraisals are still being conducted using basic price forecast techniques. This includes fixing prices in real terms based on recent evidence or forecasting prices based on a return to average or trend. Only a limited number of appraisers appear to favour more dynamic forecasting techniques, mentioned as econometric modelling. The survey results note that appraisers and their clients are wary of more dynamic price forecast methods and prefer stable trends over short term or cyclical volatility. Five price forecast techniques favoured by appraisers were developed into forecast models using real world data. This includes four basic and one dynamic price forecast method. Data from the period 2000 to 2014 was used to develop these models while data from the period 2015 to 2022 was used to validate the models. Using past data allowed testing the accuracy of the different forecast models against the actual prices achieved since 2014. The period analysed includes the explosive price period observed due to the COVID Pandemic and allowed referencing model limitations when dealing with such unexpected events. An analysis of the different price forecast models determined that a dynamic price model is better at predicting future prices and value estimates compared with basic price models. Dynamic price models do have their limitations and should be used with care. For a more dynamic approach to work, it is important to use and test outcomes using sound economic reasoning, as a correlation between variables does not necessarily equal causation. Ultimately, the market environment and the way products are traded is the most important indicator of which price forecast method to use. A decision matrix is proposed to help appraisers select the appropriate method under different market conditions. https://scholar.sun.ac.za The recommendations for using price forecast modelling from this study includes. • Even though appraisers have a strong preference for stable trends, they should not limit themselves only to basic forecast techniques. While informed market participants acting in their own best interest are not likely to consider highly speculative pricing models, they just as likely won’t consider overly simplistic pricing models either. Appraisers should emulate the way market participants price assets when considering which price forecast method to use. • A dynamic price model is best at emulating the market. It requires an appraiser to not only consider price trend but requires a much deeper understanding of supply and demand fundamentals impacting the market products are sold into, including potential developments likely to impact future prices. • Even if a more dynamic approach leads to applying a basic price trend, the process followed is important as it helps improve confidence in the final price outlook. • Developing a dynamic price forecast model can be resource intensive and may make limited financial sense, especially if the outcome cannot be justified clearly. A dynamic price model therefore works best in open markets with access to good quality data. • Basic price forecast models, such as those fixing future prices based only on current or nearterm prices, is risky in times of price change and should be avoided. Such methods have a limited place, but only in times of market stability.
- ItemCambial responsiveness in four eucalypt varieties to onset of drought as well as spring conditions(Stellenbosch : Stellenbosch University, 2024-02) Nevhungwili, Mashudu Lucy; Drew, David Michael; Eckert, Michelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT:Xylogenesis is a highly dynamic and seasonal process resulting from variations in cell production by the meristem (vascular cambium). This process results in the formation of secondary xylem and phloem cells within the period of active wood formation, leading to increased stem radius. This study explored secondary wood formation amongst four Eucalyptus varieties (Eucalyptus grandis, Eucalyptus grandis x nitens, Eucalyptus grandis x urophylla and Eucalyptus urophylla)in response to change in environmental conditions. It focussed on two study periods (an induced drought and spring period)in order to see how sensitive the varieties are to drought along with the responsiveness of the varieties to change in growth conditions during spring. To answer these questions, two-year old trees growing in an uncontrolled environment with Mediterranean climate were monitored during drought induced (March) and spring growth (August-September) seasons of 2022. Repeated wood core sampling, together with diameter change measurements, were carried out twice a week during drought induced period and once a week during spring period. Environmental data was obtained from a weather station placed adjacent to the trees. From the selected trees wood samples were extracted using a Trephor corer in a descending spiral pattern. Microcores were cut, stained, and fixed in the laboratory to produce anatomical sections, which were then observed under both Brightfield and Fluorescence microscopic imagery. The developing zone width (cambial and expanding cells zone) along with the cells in two stages of xylogenesis (cell division and differentiation) were analysed using QuPath. The results of the drought induced period showed that irrigation suspension had the greatest effect on wood formation in all studied varieties. Trees experiencing stress showed a decreased cell production as drought progressed, indicating ceased cambial activity, resulting to narrower developing zone contributing to a decreased tree size. After temporal irrigation during this period, varieties showed recovery which was observed in both stem radius and cell production. The response in the developing zone was however delayed in Eucalyptus grandis x urophylla and Eucalyptus urophylla. The response to irrigation application showed that the cambium of trees was in an eco-dormancy stage before irrigation application. The results on irrigated trees during spring period showed an active cambium during late-winter to early spring with no spring start up evident. Rainfall during this season did not show noticeable effects on wood formation across all varieties. The response of the varieties showed different maximum temperatures for wood formation during spring period. Eucalyptus urophylla showed to be sensitive to daily temperatures of above 16°C, while other varieties were sensitive to temperatures above 17°C. Results from this study lead to the conclusion that secondary wood formation in Eucalyptus varieties growing in the Mediterranean climate is controlled by how favorable the environment is.
- ItemRetrospective determination of exposure temperature of standing trees during wildfires with Solid-state NMR(Stellenbosch : Stellenbosch University, 2024-02) Kutzer, Karl; Meincken, Martina; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: Timber plantations across the world are suffering from the effects of increasingly frequent wildfires, which potentially degrade the wood of affected trees, depending on the exposure temperature. However, it is rather complicated to determine the exact temperature of the fire, or the temperature to which the wood behind the bark was exposed. This study aimed to determine the exposure temperature of the wood retrospectively through Solid-state NMR (ssNMR) analysis. Models were developed from softwood and hardwood samples exposed to defined temperatures in a laboratory furnace, which successfully linked the NMR signal to the exposure temperature. Various equations were tested to fit either the half-width or peak area of the NMR signals obtained for different exposure temperatures and the best models were identified. The results show a clear difference between Pine and Eucalyptus wood: for Pine the half-width of the NMR signal yielded the best correlation to exposure temperature, while for Eucalyptus the peak area was a better fit. The results confirmed findings of an earlier pilot study performed on Pine with an increased sample number over a larger temperature range and extended the model to a hardwood species, namely Eucalyptus. This non-destructive method offers a valuable evaluation method to determine, if the wood from burnt trees is still sound and can be further processed. If models are developed for the relevant species used by the South African Forest industry, significant economic gains can be made, by not unilaterally discarding burnt trees where the wood of many trees has not been degraded and can still be utilized.
- ItemImproved pallet base designs for citrus export : a structural and airflow study(Stellenbosch : Stellenbosch University, 2023-12) Rust, Michiel; Wessels, Coenraad Brand; Berry, Tarl; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: The overall aim of this study was to investigate and develop pallet base designs for the citrus export industry that have sufficient mechanical strength and stiffness to handle the rigors of the export process. Pallet designs should also facilitate good airflow penetration for an efficient cold chain during shipping. Six existing pallet designs were tested for strength and stiffness performance to obtain a baseline data set. Airflow penetration was also modelled for these designs. An existing pallet testing rig that has the capability of testing various aspects of pallet strength and stiffness, was used to evaluate racking bending strength/stiffness, forklift bending strength/stiffness, and impact strength. Results from these tests assisted with the identification of weaknesses in each of the pallet designs. The information was used to create improved pallet designs which were subsequently manufactured and compared to the original designs. In designs where the thickness of the structural members were increased, it resulted, as expected, in a stiffer pallet. The most breakages occurred in the stringers and especially where there were knots present on the stringer, indicating that this specific member should be a focus of improvement. The orientation of the deck boards also played a role in the stiffness of the pallet as it affected the orientation of the corner blocks. If the corner blocks were parallel to the length of the pallet, they effectively reduced the span of bearers and therefore increased the pallet stiffness. In the improved designs, an extra nail was added on the corner block for better impact performance. This inadvertently increased pallet stiffness by aiding the connections between the bearer and the corner blocks. Mixed species pallets, where Eucalyptus grandis stringers were used with other members being Pinus, also resulted in stiffer pallets. The accuracy of the nailing pattern had a large effect on the performance of the pallet during impact testing. Airflow of all the improved pallets could be enhanced by better slat spacings. Apart from improving pallet designs, it is recommended that the manufacturers and buyers of pallets should implement more stringent quality control measures. A citrus pallet quality control working group consisting of users and manufacturers of pallets can aid in this process and should be considered by the South African citrus industry.
- ItemOut-of-plane strength and stiffness prediction of SA pine cross-laminated timber(Stellenbosch : Stellenbosch University, 2023-03) Jacobs, M. J.; Wessels, Brand C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: South Africa recently adopted a slightly adapted version of ANSI PRG 320:2019 as a standard for performance-rated cross-laminated timber (CLT) – with a local code number of SANS 8892:2020. In ANSI PRG 320:2019 and SANS 8892:2020 there is a table containing unfactored resistance values for standardized CLT layups manufactured with different grades of timber in both the major and the minor strength directions. The grades of timber used in the laminations to produce the unfactored resistance tables are those available in the United States of America and, therefore, this table does not apply to the South African standard as different species of timber under different conditions are used here. Most importantly, South Africa uses a different structural timber grading system. The use of locally grown species to manufacture CLT will ensure that CLT becomes economically feasible and competitive as a high-value green alternative for reinforced concrete. Optimal design will only be possible if sufficient knowledge of local species, and how they perform in the context of CLT, is available. In this study, the locally grown SA pine was used to manufacture CLT specimens which were evaluated for bending and shear stiffness and strength, in both the major and minor strength directions. Bending evaluation was done at a span:thickness ratio of thirty with a 4-point bending test. Shear evaluation was done at a span:thickness ratio of six with a 3-point bending test. The specimens tested consisted of two 3-layer layups with respective thicknesses of 66 mm and 138 mm; these layups relate to layer thicknesses achievable by using the smallest and largest commonly available timber-lamella thicknesses in South Africa. A total of ten specimens for each layup, test and orientation combination were evaluated. The experimentally obtained results were then compared to analytically predicted stiffness results from the most widely used analytical predictive models, namely the shear-analogy and gamma methods. Where possible, all the input parameters for the predictive modelling were determined beforehand to make predictions as specific and accurate as possible. It was found that the shear-analogy method is more broadly applicable and can be used for all span:depth ratios, while the gamma method only produced accurate predictions of bending stiffness for long span:thickness ratios where the percentage of shear deformation was small. Based on the comparisons presented in this thesis, the shear analogy was chosen and used to create an unfactored resistance table for 3- and 5-layer layups using South African-strength class and lamination thickness as inputs. The thinner 66 mm CLT specimens had significantly higher bending and shear strength, and higher bending stiffness when compared to the 138 mm CLT. High rolling-shear strength values were found when compared to values found in literature for European spruce. The main outcomes of this work were (a) the proof that the shear-analogy method was a more broadly applicable prediction model for CLT lay-ups and (b) the creation of unfactored resistance tables for 3- and 5-layer layups using South African pine CLT. Future work should include the determination of rolling- shear modulus and strength of the SA pine resource, with a larger number of specimens from various regions and grades. Furthermore, the influence of layups on mechanical properties should be explored when comparing 5-layer layups to the 3-layer layup. Ways of increasing the effective stiffness of CLT plates in the out-of-plane configuration should be explored, with one such example being the addition of ribs in the long-span direction to increase stiffness.