The Hans Merensky Chair in Advanced Modelling of Eucalypt Wood Formation
Understanding xylogenesis in the world's most widely planted hardwood species
EucXylo Projects
A number of EucXylo research projects are currently ongoing, with more being added all the time!
See below for brief descriptions of some of our current and concluded projects:
Current Projects
The physiological and genetic underpinnings that influence the secondary growth of Eucalyptus grandis, when subjected to different levels of water availability
Researcher: Mr Rafael Keret (Ph.D. candidate)
Considering that wood is an incredibly valuable source of renewable biomaterial and biofuel products, it is essential that we understand how the underlying mechanisms that drive wood formation function, to apply this knowledge to the improvement of the quantity and quality of wood. In the context of Eucalyptus, water availability seems to be an essential factor that governs eucalypt wood properties, and consequently the productivity thereof. In order to cope with variations in water content, eucalypts have evolved mechanisms to induce structural changes in the xylem tissue to account for these changes. This study will focus on building an understanding of xylogenesis in eucalypts, in response to water surplus and deficit. To do so, the changes in morphological features, gene expression and protein translation will be compared between E. grandis plants that are experiencing drought and well-watered conditions. This differences in stem sections may offer clues as to how the structures of the cells confers an adaptation during water deficit. Furthermore, an “omics” (transcriptomics) approach will enable us to identify genes that underpin these morphological features and will offer clues as to how these changes are brought about. The localisation of proteins that are encoded by these genes may provide further evidence to determine what are the main drivers that influence stem structure in Eucalyptus.
Cambial responsiveness in four contrasting eucalypt varieties to varying environmental conditions
Researcher: Ms Lucy Nevhungwili (M.Sc. candidate)
Wood (xylem) formation is an important process in determining the productivity of a forest ecosystem. Wood is formed continuously in the meristem known as the vascular cambium, and the process varies in response to changing environmental conditions. This is true of the important genus Eucalyptus which is widely grown for wood production. A better understanding of the physiology of wood formation at a cellular level is important in order to improve the interpretation of species productivity and wood property variation in eucalypt species in different areas. This study will focus on understanding the behavior of the vascular cambium and developing xylem in four Eucalyptus varieties (Eucalyptus grandis, Eucalyptus grandis x urophylla, Eucalyptus grandis x nitens and Eucalyptus urophylla) under developing drought and during the onset of spring and summer conditions. The study will contribute to the estimation of parameters for wood formation models.
Xylem development in Eucalyptus cladocalyx under cyclic drought conditions
Researcher: Ms Gugu Gama (Ph.D. candidate)
This project aims to explore the development of xylem in Eucalyptus cladocalyx focusing on the relationship between cambium growth, exposure to cyclic drought and varying temperature changes. Data has been collected for sixty E. cladocalyx seedlings that were exposed to several drought treatments and temperature variations. Images of the cambium of these seedlings were captured using polarizing light microscopy as well as bright-field microscopy. ImageJ is currently being used to analyse the changes in the cambium at the different stages of the drought treatment, and a study aim is to develop a method of capturing the dynamics of xylem development from image data. A further aim is to compare the E. cladocalyx results to those from Eucalyptus species that are not drought-tolerant, to identify the key differences characterising xylem development under water-stressed conditions.
Radial variation in wood properties effected by environmental factors and silvicultural regimes influencing collapse and shrinkage in Eucalyptus grandis
Researcher: Mr Matthew van Eyssen (M.Sc. candidate)
As South Africa is a timber-scarce country, it is not surprising that there is predicted to be a shortage of softwood timber within the next 10 years. One of the solutions under investigation is to use hardwoods – mostly Eucalyptus – as structural timber, as they are relatively plentiful in South Africa. One of the biggest underlying problems with this approach is that this genus is prone to cell wall collapse and excessive shrinkage, leading to major problems in the sawmills due to the deformed wood planks. I aim to investigate candidate wood properties suspected of influencing cell wall collapse in E. grandis, looking at environmental factors and silvicultural regimes that influence these wood properties. With this data we will have a better understanding of the ‘cause of the causes’. This will provide us with the necessary knowledge to suggest different silvicultural techniques if needed for the purpose of growing E. Grandis with wood less prone to collapse.
Advanced imaging of developing xylem
Researcher: Dr Letitia Schoeman (Postdoctoral Research Fellow)
Knowledge of the process by which the cambium produces wood has progressed very slowly and this knowledge gap is largely due to difficulties in visualising the 3D organisation of the cambium and the lack of non-destructive methods with sufficient resolution to study the developmental processes of wood formation. Non-destructive visualisation of the developing xylem in living, growing plants is an exciting frontier. This project is mainly focused on exploring and assessing various approaches to non-destructively visualise and quantify the developmental processes in differentiating xylem in eucalypts, making use of cutting-edge techniques such as X-ray micro- and nano-CT, MRI, PET, and confocal and correlative microscopy. The goal would be to visualise and characterise the properties of living xylem quickly and repeatedly, with as little damage to the tree as possible to better understand how eucalypts form their wood. Ultimately, an ideal outcome would be to develop one or more of these approaches to enable imaging of living cambial cells and differentiating xylem.
The effects of temperature and water availability on the water use efficiency of two Myrtacae species, Eucalyptus grandis and Syzygium guineense
Researcher: Ms Yenziwe Mbuyisa (M.Sc. candidate)
The opportunity of climate change mitigation through global tree afforestation/reforestation programs has become the flavour of the decade. With the likelihood of increasingly frequent and severe droughts and heat waves being a major cause for concern, understanding how trees respond to temperature extremes and limited water availability is critical to forecasting both short and long-term impacts of climate change on forest systems in South Africa. This study will evaluate the effects of ambient air temperature in concert with available water availability on the water use efficiency (WUE), physiology, and isotopic discrimination of two Myrtacae species; Eucalyptus grandis (a species originally from New South Wales) and Syzygium guineense (a local species found predominantly in the eastern parts of South Africa). The trees will be placed in a high tunnel structure where they will be exposed to a temperature gradient stimulated by a built-in wet wall. Two water treatments will be applied to the trees to help determine whether WUE varies between the two species under different temperatures and whether δ13C can be used as a reliable signal of historic WUE.
Carbon allocation and biomass accumulation within eucalypt clones with contrasting water use strategies
Researcher: Mr Chris Tonkin (M.Sc. candidate)
Eucalypts are some of the fastest growing and most productive trees. This could potentially make them a viable option for removing CO2 from the atmosphere and helping to mitigate the effects of climate change. However, the basis for their high productivity is not yet well understood but it has been noted that their productivity rates are often limited by drought conditions. Chris’ project is focused on studying the physiological processes of carbon uptake, biomass allocation and water use efficiency between a fast-growing varietal (Eucalyptus grandis x longirostrata) and a drought tolerant varietal (Corymbia henryii x torelliana). He will further explore how drought conditions will affect these physiological processes in a semi-controlled greenhouse study.
Eco-physiological interactions and resultant variability in xylem properties in four contrasting Eucalyptus clones
Researcher: Mr Mpilo Khumalo (Ph.D. candidate)
This project explores the very short-term eco-physiological responses to variability a range of environmental conditions in four Eucalyptus hybrids. The work is ultimately concerned with elucidating how these short-term responses in phenomena like transpiration, stem growth, expansion and contraction, stomatal conductance and photosynthesis influence the properties of xylem formed. And importantly, what are the differences and similarities between the four varieties? The experimental set-up was designed to specifically consider two sets of contrasts. Firstly, E. grandis, in contrast with hybrids between the cold-tolerant E. grandis x E. nitens, and the sub-tropical hybrid E. grandis x E. urophylla. Secondly, E. grandis, and E. urophylla, in contrast with the hybrid between these two species. The trees are heavily instrumented with dendrometers, HPV sap flow, Sentech soil water and temperature probes and there is an automatic weather station adjacent to the trees measuring the full gambit of climatic variables.
Developing climate sensitive models for predicting future forest growth, yield and wood properties in Eucalyptus plantations
Researcher: Mr Brian Mandigora (Ph.D. candidate)
Short- and long-term planning of commercial forest rotations involves the use of empirical growth and yield models. Despite the general reliability of these models in performing their intended functions, they do not account for climatic variability, which is a major drawback under the current conditions of climate change where weather is highly variable and unpredictable. Moreover, it is not fully understood how short-term environmental and climatic events affect wood quality at the end of rotations. The frequent occurrence of droughts in South Africa has made it difficult to predict forest yields based on past rotations, hence intervention tools are necessary. Brian’s project seeks to develop models that explain growth, yield and wood properties at appropriate spatial scales in the KwaZulu-Natal region of South Africa. These will provide forest managers with decision and operation tools in the face of climatic variability.
Using a Knowledge Graph approach to link metadata from forestry models and datasets, to assist analysis and hypothesis generation
Researcher: Dr Kim Martin (Postdoctoral Research Fellow)
Forestry research has a rich history of computational models and datasets that cover a wide range of interacting scales. It was highlighted during a 2020 meeting of the Quantitative Wood Anatomy Network (Q-Net) – in a session titled ‘Modelling & QWA: From Cell To Ecosystem’ – that it is challenging for researchers of wood formation and ecophysiology to develop an integrated understanding of the models available (including how they could possibly be composed together). This project aims to assist researchers in the field of eucalypt wood formation and ecophysiology to explore datasets and computational models in a flexible and integrative way. The goal is to encompass models of phenomena at different scales; ranging from process-based models of the cellular determinants of wood formation, to empirical models of gross tree growth in different environmental contexts. The linked information should allow complex questions to be asked, including: how similar models differ; which datasets can be repurposed to test different model outputs; and identifying whether and how different models can be composed together. This will promote open scientific practices in this research area (through the use of common metadata standards and terms), and may serve as a valuable framework for collaborative knowledge capture and exploration.
Concluded Projects
Investigating the photosynthetic and hydraulic trade-off during drought recovery in eucalypts
Researcher: Mrs Alta Saunders (Ph.D.)
Stomatal regulation plays a key role in controlling carbon sequestration and water loss and it can be argued that stomata have evolved to balance this trade-off. The regulation of stomatal conductance in leaves are also highly affected by hydraulic changes within a plant, and a plant must constantly balance water dynamics while maximizing carbon uptake. Plant water supply, a major factor in understanding plant-level carbon sequestration, is not only regulated by stomatal conductance, but also limited by a decrease in hydraulic conductance due to embolism formation. The reduction of xylem conductance due to embolism formation cannot be directly regulated by the plant. However stomatal regulation can help prevent runaway cavitation. Understanding plant stomatal and hydraulic responses to water availability, can help improve predictions of plant productivity. Alta’s Ph.D. therefore focused on how plants respond to drought and recovery after drought, as well as what the role is that stomatal conductance play in drought responses seen within Eucalyptus.
Performance of process-based models in predicting productivity of Eucalyptus grandis x urophylla in South Africa
Researcher: Mr Oluwaseun Gakenou (M.Sc.)
The 3-PG model, a simple process-based model (PBM) has gained popularity with researchers and forest resources managers (especially pulp growers in South Africa) as a practical tool for sustainable forest management strategies. This is because the classical growth and yield models used have become unsustainable as we are in a time where forest growth cannot be reliably predicted from historical bioassay. This project aimed to test and set up the 3-PG model for Eucalyptus grandis x urophylla (the most planted hybrid clones by the forest industries in South Africa) and compare its performance with the currently used conventional growth and yield model. The outcome from this project was to recommend an operational tool for forest managers, which can accurately predict the growth and yield under changing environment and management practices, provide data useful in the economic management of stands, predict the productivity of a new site that has not been previously afforested.
Prediction of the future biomass of Eucalyptus plantations in Zululand
Researcher: Mr Tiza Mfuni (M.Sc.)
Tiza’s M.Sc. project is aimed at predicting the future volumes and potential shifts in site suitability of Eucalyptus grandis x urophylla in coastal Zululand, based on projected climate scenarios according to two Representative Concentration Pathways (RCPs) as described in the latest Synthesis Report by the Intergovernmental Panel on Climate Change (IPCC). The project will explore the use of outputs from selected downscaled Global Circulation Models (GCMs) over coastal Zululand as inputs into the 3-PG (Physiological Processes Predicting Growth) stand level model. In its ability to predict future volumes in different future climate scenarios, Tiza’s project will contribute to the preparedness of the South African timber industry to anticipate and mitigate climate variability.
See the EucXylo Research Opportunities page to learn more about the areas our group focuses on.