School of Agriculture, Food and Ecosystem Sciences - Theses

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Start date: 1960 × Subject: climate response × Subject: growth ×

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    Phenological responses of select Eucalyptus species to environmental variability
    Rawal, Deepa Shree ( 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 1C for E. microcarpa and E. tricarpa) while the cool-moist species exhibit a delay in flowering (8.7−14.1 days per 1C 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.