The chemistry of Australian soils and the affect features of Australian native vegetation
The chemistry of Australian soils and the affect features of Australian native vegetation
Australian soils and vegetation
Australia has had a long stable geological period (60 million years) which has created soils that have been described as old, climatically buffered and infertile (Lambers, et al., 2011). Low soil nutrients are reflected in plant structures that support them (Clarkson, et al. 2011; Stock & Verboom, 2012). Plants growing on these soils have characteristically low foliage nutrients and slow growth rates and greater biodiversity (alpha diversity) than younger more fertile soils (Specht, et al., 2006).
Soil is an important determiner of local scale composition and richness affecting species variation but not species abundance (Herrera & Finegan, 1997). Individual tree species can have a significant preference for either fertile or infertile soils in tropical forests (Gleason, et al., 2010). Soil affects community composition at regional scale and species richness at landscape scale and beyond (Eiserhardt, et al., 2011). Spatial variation of soil nutrient availability, rather than total soil nutrient contents, are suggested to be important in explaining landscape-level species distributions and community composition in nutrient poor Mediterranean climate ecosystems (Richards, et al., 1997).
Plants growing on infertile soils are more likely to show symptoms of P-toxicity when exposed to slightly elevated levels of soil P (Lambers, et al., 2011). Plants adapted to infertile soils also have a greater P-use efficiency (Gleason, et al., 2009) compared to plants typical of younger more fertile soils (Lambers, et al., 2011). P availability has been found to create plastic responses within species and regulate net primary production and other ecosystem processes in lowland tropical and rainforest soils in Australia (Gleason, et al., 2009) and elsewhere (Paoli, et al., 2005; Cleveland, et al., 2011).
Other significant plant adaptations from low fertility soils are high N:P ratios and a high LMA (leaf mass per unit leaf area) value and leaf lifespan (Wright, et al., 2002; Lambers, et al., 2011). Salinity, pH and physical soil features are less commonly studied (Medinski, et al., 2010). Soil pH gradients and light availability were found to have some effect on juvenile recruitment (Penfold & Lamb, 2002). Changes to P and N showed no effect on adult growth rates (Prior, et al., 2012).
In nutrient poor grasslands, light availability has little effect on grasses as competition for nutrients is more important in this ecosystem (Ba, et al., 2006). In tropical forests, nutrient cycling is significantly affected by species-soil and species-disturbance interactions (Gleason, et al., 2010). To maintain the nutrient cycle, plants on nutrient-poor soils leach nutrients more slowly than plants on younger soils (Sangha, et al., 2006).
Soils changes over time as vegetation changes. As rainforest invades wet sclerophyll forest, the soil beneath the invading rainforest becomes increasingly similar to rainforest soil (Warman, et al., 2013).
Adaptations to nutrient poor soils can also be found in Southern Africa (Richards, et al., 1997; Clarkson, et al., 2011) and Mediterranean climates (Stock & Verboom, 2012). Laliberté et al. (2013) provides a thorough explanation of how aged soils influence local plant species diversity.
(authors: Pheona Anderson and Ben Wilson).
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As with all assessments in subjects, their rationale is to assess your knowledge against the stated Learning Outcomes in the subject’s information. The learning outcomes of this subject are focussed on knowledge acquisition, rather than say specific field or laboratory technical skills. As such these learning outcomes could be assessed with a 3 hour exam, however, the difference with exams is that a bibliographic essay should produce a greater understanding of the subject content because you are required to engage with a much wider array of information than just what is covered in lectures or modules, and it’s your task to group the information into themes and analyse the information in a way that requires some intellectual input, rather than just a good memory.
However, the other rationale for this type of assignment, is that it is much more authentic. This refers to assessments that are more closely aligned to the types of activities you may do in your professional life after graduation. While it may not be so obvious to you at this stage in your studies, being able to summarise, synthesise and evaluate literature is a key skill in most professional positions in environmental or protected area management. This is often done to provide the required background information when assessing an environmental issue, the conservation status of an animal, the policy background to a government decision or when determining the impact associated with some development or other human activity.
For the major assignment, you will produce a bibliographic essay exploring the above topic.
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