School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemPhenological responses of select Eucalyptus species to environmental variability( 2014)The Earth’s climate is warming which will likely lead to changes in biological systems; particularly to species physiology, phenology and distribution. Phenology is the study of life cycle events of plants and animals (e.g.plant germination/ leafing/ flowering; bird migration/feeding) that is directly ruled by seasonal changes in climate. The phenological responses of species are typically sensitive to climate and can be drivers of plant distributions. In Australia, significant research gaps exist on species phenology as extensive and long-term datasets are lacking. A lack of datasets and observational studies highlights key knowledge gaps on the relationship between climate and species phenology, which in turn may limit our ability to predict the response of species to climatic change. This study investigates the key environmental drivers that affect three phenological cycles; germination, growth and reproduction (flowering) of six Eucalyptus species that co-occur in two groups, representing dry (warm-dry) and wet (cool-moist) sclerophyll forests of south-eastern Australia respectively. The six species studied were E. microcarpa, E. polyanthemos, E. tricarpa, E. obliqua, E. radiata and E.sieberi; the first three species representing the dry and the later three the wet sclerophyll forests. The study seeks to identify the relationships between these phenological events and the environmental factors temperature, soil moisture, air humidity and photoperiod length. In particular, the study seeks to identify environmental thresholds that initiate or delay phenological events. Experimental and statistical approaches were used to identify phenological response parameters for each phenological stage. Significant effects of environmental factors on germination, growth and flowering phenology of the studied species were found across all the species, however, the extent and response mechanisms varied amongst species, highlighting that some species may be more susceptible to environmental change. Based on the GCM predictions of future climate the climate change scenarios were built where temperature increases ranging from 0.4−2.75 C with a 1−9% decline in rainfall are expected to incur by the 2020s. For the 2050s, the temperature increase ranges from 0.75−2.75 C with a 3−25% decline in rainfall and for the 2080s temperature increase ranges from 1.0−4.5 C with a 4−40% decline in rainfall.The germination phenological study identified that among warm-dry species, greater germination and establishment may be exhibited by E. microcarpa under warm and dry condition of climate change. Among cool-moist species germination increased for E. obliqua under warm and dry condition of climate change, however, establishment declined. For all the species in the cool-moist group establishmet declined rapidly by the 2050s, though E. radiata exhibited capacity to establish until the 2080s. Non linear growth responses to temperature and temperature thresholds were identified using a Generalised Additive Model (GAM) analysis of 12 months of tree growth, collected from a climate-manipulation experiment study conducted in four glasshouses.The study found that amongst the warm-dry species, E. microcarpa exhibited greater resistance to high temperatures and lower air humidity conditions. E. obliqua exhibited a flexible growth rate and tolerance to moisture limitations. Temperature-dependent photoperiodic responses were quantified for all the species except E. tricarpa and E. sieberi. The flowering phenological study found that non-linear effects of temperature, rainfall and photoperiod length affected flowering intensity. The study showed that E. microcarpa displayed phenotypic plastic response to higher temperature and lower rainfall conditions. Rainfall was influential for E. polyanthemos and E. tricarpa, while flowering and umbel budding of E. obliqua increased when rainfall decreased. This study also identified temperature-dependent photoperiodic cues for all the species with flowering in E. polyanthemos reliant on longer photoperiod lengths. The longer photoperiodic cues found for E. polyanthemos suggests the species is reliant on summer conditions for flowering, however, climate change may increase summer temperature conditions which may pose a risk to the flowering. Long-term flowering phenological data sets are rare for Australian species. An analysis of flowering data using herbarium records in this study demonstrated that the herbarium approach can detect climatic effects on flowering phenology. The study identified that temperature has the largest influence on flowering time although the impacts vary among species, with the warm-dry species exhibiting earlier shifts in response to increasing temperature increment (14.1−14.9 days per 1C for E. microcarpa and E. tricarpa) while the cool-moist species exhibit a delay in flowering (8.7−14.1 days per 1C for E. obliqua, E. radiata and E. sieberi). Both the flowering dataset and herbarium approaches identified that flowering phenology of E. polyanthemos was sensitive to the majority of environmental variables. This study attempts to address the role of phenology on species distributions by integrating the germination, growth and flowering phenological response to model plant response. Phenological trait responses derived from all three studies were combined with 50 years of climate data from each species home range and climate change predictions for south-eastern Australia into the mechanistic model TACA-GEM to create the model variant TACA-PHENO (sub modules of growth and flowering phenological response added to TACA-GEM). The modelling analysis demonstrated that changes in species germination probability, yearly growth and monthly flowering intensity can be detected under observed and climate change scenarios. The results show that for the warm-dry species E. microcarpa, all three phenological stages may be positively influenced by warmer and drier condition of climate change, indicating that the species will maintain and/or increase its distribution in the future. Distributions of all the other species may constrict, however, as one or more phenological responses were negatively affected by climate change. The current distribution of E. tricarpa was the most vulnerable to warming and drying of climate change as germination failed by the 2050s. The phenological strategy of the cool-moist species E. radiata indicates that the species may maintain or increase its current distribution, compared to E. obliqua and E.sieberi by the 2080s. This study highlights that species exhibit divergent phenological responses to environmental conditions; linking all these responses with a modelling approach can help to identify species sensitivity to environmental change. The study high lights that species phenology will remain responsive to changes in temperature and moisture across the spatial scales and thus will be sensitive to climate change. The implications of this phenological shift on species adaptation to climate change is complex, however, our study was successful in providing some initial insights on how climate change may vary phenology which in turn may affect the species abundance in the future.
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ItemStudies of the germination of seven Australian alpine and subalpine shrub species( 1998-03)Seeds of seven alpine and subalpine Australian shrub species (Acacia alpina,A. obliquinervia, Bossiaea foliosa, Hovea montana, Oxylobium ellipticum,Grevillea australis & Pimelea ligustrina) with potential to colonise in badly disturbed alpine and subalpine sites had a range of treatments (scarification,stratification, leaching, chemical soaks, freezing & diurnally fluctuating temperatures) applied to them to enhance germination success. Seeds of the hard seeded legumes responded well to scarification and stratification treatments. Acacia obliquinervia was scarified with boiling water which resulted in enhanced germination success. The scarification treatment with the best result was nicking for the other four legumes. The use of hot-watersoaks for these other legumes, of a minute or less showed some potential as a useful scarification treatment Stratification periods between 8 to 14 weeks for Acacia alpina, 12 to 14 weeks for Bossiaea foliosa, 2 to 8 weeks for Hoveamontana and 4 to 6 weeks for Oxylobium ellipticum gave significantly enhanced germination. Grevillea australis did not respond to germinationpre-treatments, except for an isolated case of nicking and stratification for 6weeks. The same treatment of older seed did not result in significantgermination. Pimelea ligustrina did not reliably respond to germination pretreatments.Germination trial results were then applied to one of the legumespeCIes (Bossiaea foliosa) as a guide to how these seeds respond to apretreatment before sowing on a disturbed site at the Bogong High Plains.The treatment of 30s in water @ l00°C and 14 weeks stratification before sowing in autumn was found to significantly enhance the field establishment success of Bossiaea foliosa.
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ItemRegeneration of river red gum Eucalyptus camuldulensis Dehn( 1970)The aims of this study were to investigate the main factors influencing the regeneration of river red gum Eucalyptus camaldulensis Dehn., in Barmah forest and to use the results to develop procedures for establishing regeneration primarily for wood production. Factors influencing germination and survival of seedlings were examined. These included seed supply, seasonal conditions, seed beds, availability of soil moisture, the influence of over-topping trees, flooding and grazing. Natural seed supply is variable because the intensity of flowering varies widely and unpredictably from year to year and about 45 per cent of flowers fail to mature. Seasonal conditions are a major factor affecting germination of seed and survival of seedlings especially in the absence of flooding. On unflooded areas germination is confined to the wetter, cooler months and survival is highest if there are good summer rains. Germination and survival following flood recession are often high. When flood recession occurs late in summer, however, hot conditions may kill most seeds or young germinates. The combination of winter-spring flooding and above average summer rains favours germination and survival. In very dry years few seedlings develop and these are restricted to the most receptive sites. Ash bed and cultivated seed beds are the most receptive sites for seedling establishment and grassed and hard bare earth sites are the least receptive. Seedling establishment is also severely restricted where weeds or over-topping trees compete with seedlings for moisture. Prolonged flooding kills large numbers of young seedlings especially if they are completely immersed for some months. Flooding is uncontrollable so it is advantageous to promote rapid seedling growth and so minimize deaths or severe flood injury. During drought periods red gum seedlings may be destroyed by rabbits, kangaroos, wild horses and cattle. When feed is abundant, however, the adverse effect of all these animals is slight. Extensive grazing of cattle on regeneration areas keeps weeds that are competing with seedlings for moisture in check, and seedling mortality due to soil drought is much less than on ungrazed areas. Several techniques for regenerating river red gum were developed from the fundamental studies and were tested on an operational scale. Of the procedures based on direct seeding clear felling followed by aerial seeding is the cheapest and most flexible, and is recommended as the technique to be used generally. The major costs involved are in seed bed preparation, poisoning non-merchantable trees, collecting seed and in aerial seeding. None of these operations is expensive. Sowing rates and time of sowing are determined on the bases of expected flooding and seed bed quality. Seed beds are made receptive by removing grass and other vegetation and preparing the ground surface by slash burning and cultivation. Procedures based on natural seed supply involve preparation of seed beds and inducement of seed fall during summer and autumn, followed by utilization of merchantable and poisoning of non-merchantable trees. Because careful timing of each phase is required to suit such factors as seed maturation, seed fall and germination, the induction of seed fall can be costly and difficult to organize. Various factors that may influence the choice of the regenerative procedure are discussed. Finally, it is concluded that the provisional stocking standards are compatible with other forest values.
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ItemGermination and emergence of wild radish (Raphanus raphanistrum L.)( 2001)Wild radish is a major weed of the southern Australian wheat belt. It is difficult to control in oilseed and pulse crops, and more recently in cereal crops due to the development of herbicide resistance. Obtaining a better understanding of the seed biology of wild radish will allow the implementation of management practices that can keep weed numbers at low levels. Also, as wild radish has its seeds enclosed by a hard non-dehiscent section of pod, this is an interesting species from an ecological perspective to investigate the regulation of emergence. Anecdotal evidence suggests that wild radish differs in its periodicity of emergence to that of other major weeds of the southern Australian wheat belt. It has been theorised that the enclosing pod structure is the cause of the difference emergent pattern of wild radish. This thesis compares the emergence patterns of wild radish to other major weeds of the southern Australian wheat belt and examines the regulation of germination and emergence of wild radish. Seedling emergence is broken down into three major processes; (i) the cycling of seed dormancy, (ii) germination, and (iii) pre-emergent seedling growth. The effects of different environment conditions on each of these processes are examined. The periodicity of wild radish differs from major weeds of the southern Australian wheat belt, annual ryegrass, wild oats and spiny emex, in that wild radish emergence occurs mainly in the second season after seed release from the parent plant, whereas the other three species have the majority of their emergence in the first season. Previously the enclosing pod segment of wild radish was thought to be the major germination inhibiting factor. This thesis clearly demonstrates that the seed coat of wild radish is the primary cause of non- germination of seeds. Evidence is presented that this inhibition of germination is through the physical restriction of the embryo. The pod segment however, appears to act as an environmental buffer delaying the breakdown of the seed coat through the regulation of temperature, soil water content and light quantity. While dormancy cycling has been studied in many species, this thesis is the first to report on seeds having different cycling responses depending on the depth of burial in the soil. Very different germination responses occurred between seeds on the soil surface and buried seeds, with the former responding to periods of darkness and the latter having a light requirement. Even with buried seeds, the level of dormancy cycling changed with depth. The maternal environment dominated many seed traits, with a reduction in seed longevity when adverse conditions occurred during ripening. Evidence was presented that this decrease in longevity was associated with a decrease in seed coat thickness. The data generated by this thesis could be used as the basis of a mechanistic predictive emergence model for wild radish. For emergence models to predict field emergence effectively, dormancy cycling for different soil layers would clearly be required.