41 research outputs found

    Genetic variation and resilience to climate change in Mediterranean-type trees

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    Climate models predict that temperature means will continuously increase globally, and that heatwaves and drought periods will become more frequent and intense, particularly in Mediterranean-type climates. The Southwest Western Australia (SWWA) Biodiversity Hotspot has extensive forest environments that have been subject to heatwaves and drought-induced forest mortality in recent years, impacting forest carbon sequestration and local ecological structure. Although, species may persist through enhanced physiological tolerance, phenotypic plasticity and/or genetic adaptation. Genetic variation is critical for ecological adaptive capacity - the potential and ability to adjust to, and persist through, external factors - and consequently, the evolutionary potential of the species. Evolution to a specific environment through natural selection results in patterns of local adaptation (when a local population experiences higher fitness compared to non-local counterparts). Local adaptation can be identified by either genome wide surveys that link genetic variants to climate variables or measuring plant traits indicative of plant performance and survival through reciprocal transplants in common environments. Exploring genetic adaptation patterns associated with physiological tolerance to climate can guide forest management approaches to enhance forests’ resilience to climate change, such as assisted gene migration. The genetic survey (Chapter 2) sampled natural jarrah populations and obtained 13,534 independent single nucleotide polymorphic (SNP) markers across the genome. Three genotype-association analyses were used to identify putatively adapted SNPs associated with independent climate variables. While overall levels of population differentiation were low (FST=0.04), environmental association analyses found a total of 2,336 unique SNPs associated with temperature and precipitation variables, with 1,440 SNPs annotated to genic regions. Considerable allelic turnover was identified for SNPs associated with temperature seasonality and mean precipitation of the warmest quarter, suggesting that both temperature and precipitation are important factors in adaptation. SNPs with similar gene functions, had analogous allelic turnover along climate gradients, while SNPs among temperature and precipitation variables had uncorrelated patterns of adaptation. These contrasting patterns provide evidence that there may be standing genomic variation adapted to current climate gradients, providing the basis for adaptive management strategies to bolster forest resilience in the future. The second experimental chapter (Chapter 3) explored seed germination response to temperature in jarrah and marri populations from wide-ranging climate origins, to estimate the thermal optima and constraints. Seeds from across the entire geographic distribution were collected from independent populations of each species. Patterns of germination observed differences between species on a thermal gradient plate (5-40°C) and provided a temperature range for explicit germination tests. Germination tests were carried out at five constant temperatures between 9 and 33°C. We discuss how the germination niche (1) differs between species, (2) varies among populations, and (3) relates to climatic origin. Temperature response of germination differed among species, specifically the optimum temperature for germination (jarrah – 23.4°C; marri - 31°C). Temperature response of germination also differed among populations within species and was related to the climate-origin only for marri. Lastly, for the third experimental chapter (Chapter 4), a reciprocal transplant common garden experiment was used to investigate variation in marri`s functional traits using hyperspectral data. Hyperspectral remote sensing has the potential to assess plant functional status rapidly and non-destructively across climatic gradients to support conservation and management strategies, such as assisted migration, for forests under climate change. This study explored the variability of functional traits in marri to estimate patterns of local adaptation. Trees from natural populations spanning marri’s geographic distribution were grown in two common garden plantation sites with different climate settings. High-resolution field-based spectral measurements were collected from leaves of adult plants at both sites in two seasons (summer and autumn). Partial least squares regression analyses of full reflectance spectra highlighted differences among populations, sites, and seasons in spectral regions associated with photosynthetic pigments and water content, among other spectral traits, related to leaf condition and stress responses. Variation in these traits was further explored with analyses of spectral indices tailored to pigment and water absorptions. Analyses of spectral indices variation identified significant differences between populations, suggesting there is heritable variation in climatic tolerances, but stronger effects of season and site

    Three dimensional estimation of vegetation moisture content using dual-wavelength terrestrial laser scanning

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    PhD ThesisLeaf Equivalent Water Thickness (EWT) is a water status metric widely used in vegetation health monitoring. Optical Remote Sensing (RS) data, spaceborne and airborne, can be used to estimate canopy EWT at landscape level, but cannot provide information about EWT vertical heterogeneity, or estimate EWT predawn. Dual-wavelength Terrestrial Laser Scanning (TLS) can overcome these limitations, as TLS intensity data, following radiometric corrections, can be used to estimate EWT in three dimensions (3D). In this study, a Normalized Difference Index (NDI) of 808 nm wavelength, utilized in the Leica P20 TLS instrument, and 1550 nm wavelength, employed in the Leica P40 and P50 TLS systems, was used to produce 3D EWT estimates at canopy level. Intensity correction models were developed, and NDI was found to be able to minimize the incidence angle and leaf internal structure effects. Multiple data collection campaigns were carried out. An indoors dry-down experiment revealed a strong correlation between NDI and EWT at leaf level. At canopy level, 3D EWT estimates were generated with a relative error of 3 %. The method was transferred to a mixed-species broadleaf forest plot and 3D EWT estimates were generated with relative errors < 7 % across four different species. Next, EWT was estimated in six short-rotation willow plots during leaf senescence with relative errors < 8 %. Furthermore, a broadleaf mixed-species urban tree plot was scanned during and two months after a heatwave, and EWT temporal changes were successfully detected. Relative error in EWT estimates was 6 % across four tree species. The last step in this research was to study the effects of EWT vertical heterogeneity on forest plot reflectance. Two virtual forest plots were reconstructed in the Discrete Anisotropic Radiative Transfer (DART) model. 3D EWT estimates from TLS were utilized in the model and Sentinel-2A bands were simulated. The simulations revealed that the top four to five metres of canopy dominated the plot reflectance. The satellite sensor was not able to detect severe water stress that started in the lower canopy layers. This study showed the potential of using dual-wavelength TLS to provide important insights into the EWT distribution within the canopy, by mapping the EWT at canopy level in 3D. EWT was found to vary vertically within the canopy, with EWT and Leaf Mass per Area (LMA) being highly correlated, suggesting that sun leaves were able to hold more moisture than shade leaves. The EWT vertical profiles varied between species, and trees reacted in different ways during drought conditions, losing moisture from different canopy layers. The proposed method can provide time series of the change in EWT at very high spatial and temporal resolutions, as TLS instruments are active sensors, independent of the solar illumination. It also has the potential to provide EWT estimates at the landscape level, if coupled with automatic tree ii segmentation and leaf-wood separation techniques, and thus filling the gaps in the time series produced from satellite data. In addition, the technique can potentially allow the characterisation of whole-tree leaf water status and total water content, by combining the EWT estimates with Leaf Area Index (LAI) measurements, providing new insights into forest health and tree physiology.Egyptian Ministry of Higher Educatio

    A Clustering Framework for Monitoring Circadian Rhythm in Structural Dynamics in Plants from Terrestrial Laser Scanning Time Series

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    Terrestrial Laser Scanning (TLS) can be used to monitor plant dynamics with a frequency of several times per hour and with sub-centimeter accuracy, regardless of external lighting conditions. TLS point cloud time series measured at short intervals produce large quantities of data requiring fast processing techniques. These must be robust to the noise inherent in point clouds. This study presents a general framework for monitoring circadian rhythm in plant movements from TLS time series. Framework performance was evaluated using TLS time series collected from two Norway maples (Acer platanoides) and a control target, a lamppost. The results showed that the processing framework presented can capture a plant's circadian rhythm in crown and branches down to a spatial resolution of 1 cm. The largest movements in both Norway maples were observed before sunrise and at their crowns' outer edges. The individual cluster movements were up to 0.17 m (99th percentile) for the taller Norway maple and up to 0.11 m (99th percentile) for the smaller tree from their initial positions before sunset

    A Clustering Framework for Monitoring Circadian Rhythm in Structural Dynamics in Plants From Terrestrial Laser Scanning Time Series

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    Terrestrial Laser Scanning (TLS) can be used to monitor plant dynamics with a frequency of several times per hour and with sub-centimeter accuracy, regardless of external lighting conditions. TLS point cloud time series measured at short intervals produce large quantities of data requiring fast processing techniques. These must be robust to the noise inherent in point clouds. This study presents a general framework for monitoring circadian rhythm in plant movements from TLS time series. Framework performance was evaluated using TLS time series collected from two Norway maples (Acer platanoides) and a control target, a lamppost. The results showed that the processing framework presented can capture a plant's circadian rhythm in crown and branches down to a spatial resolution of 1 cm. The largest movements in both Norway maples were observed before sunrise and at their crowns' outer edges. The individual cluster movements were up to 0.17 m (99th percentile) for the taller Norway maple and up to 0.11 m (99th percentile) for the smaller tree from their initial positions before sunset

    Operationalization of Remote Sensing Solutions for Sustainable Forest Management

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    The great potential of remote sensing technologies for operational use in sustainable forest management is addressed in this book, which is the reprint of papers published in the Remote Sensing Special Issue “Operationalization of Remote Sensing Solutions for Sustainable Forest Management”. The studies come from three continents and cover multiple remote sensing systems (including terrestrial mobile laser scanning, unmanned aerial vehicles, airborne laser scanning, and satellite data acquisition) and a diversity of data processing algorithms, with a focus on machine learning approaches. The focus of the studies ranges from identification and characterization of individual trees to deriving national- or even continental-level forest attributes and maps. There are studies carefully describing exercises on the case study level, and there are also studies introducing new methodologies for transdisciplinary remote sensing applications. Even though most of the authors look forward to continuing their research, nearly all studies introduced are ready for operational use or have already been implemented in practical forestry

    Optimised eucalypt domestication : an example using e. Cladocalyx, a species for low rainfall environments

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    Eucalyptus cladocalyx is endemic to South Australia and has been planted extensively on farmland throughout southern Australia and in dry, Mediterranean climates overseas. Its wood is hard, strong and naturally durable, making it suitable for fuelwood and solid-wood applications. Domestication in Australia commenced in 2001, when 11 provenance-progeny trials were established. The breeding objective is to maximise sawlog production per hectare per year. This thesis, presented as six chapters, examines genetic aspects of these trials that will influence the future direction of the species' domestication program. Chapter 1 argues that traditional methods and assumptions historically used to identify selections in the first-generation breeding programs of the main commercial tree species can be improved upon in the following ways: (1) Examination of wood properties (in addition to growth and form traits) during the first generation, taking advantage of modern labour-saving techniques, rather than delaying until later generations when unidentified adverse genetic correlations between traits may be problematic. (2) Employing molecular markers to determine population genetic parameters and reconstruct pedigree and inbreeding information from families that have unknown or uncertain ancestry. (3) Using recently-developed mixed-modelling techniques that allow integration of marker-based pedigree and inbreeding information to model genotype-by-environment (GxE) interactions using large datasets. Chapter 2 examines genetic parameters including heritability of growth and wood natural durability traits and additive genetic correlations among traits. The use of near infrared reflectance as a low-cost method of screening durability traits such as decay mass loss and wood extractive content is also investigated. Chapter 3 examines the use of marker-based data to modify traditional assumptions made in analysis of first generation breeding populations. Previously published growth-trait estimates, together with an earlier isozyme study, indicated that the traditional approach may give upwardly biased heritability estimates due to high and heterogeneous selfing. Models were implemented that compared the approach of treating families as half-sibs with analyses based on previously existing isozyme estimates of heterogeneous family outcrossing to modify pedigree assumptions. The results of genotyping mature trees from the majority of families in the breeding population using single-nucleotide polymorphism (SNP) markers are presented in Chapter 4. Population structure and diversity, family relatedness, inbreeding and inbreeding depression were investigated. Chapter 5 integrates the marker-based estimates of family-level relatedness and inbreeding of Chapter 4 into a quantitative genetic analysis across sites using an extension of the methodology developed in Chapter 3. Individual-tree mixed models based on (i) the traditional half-sib family assumption and (ii) a modified mixed model incorporating marker-based data were compared. Analysis of GxE was performed across the 11 sites using individual-tree, factor analytic mixed models. Chapter 6 concludes that the prospects for genetic improvement of E. cladocalyx are good, due to ample, heritable genetic variation and absence of adverse genetic correlations among traits. Analyses with integrated molecular marker data were significantly improved, as traditional models were unsuitable due to the breeding population's heterogeneous and unusually high levels of inbreeding. Integration of marker data into first-generation analyses of eucalypt breeding populations is likely to find wider application in future
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