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).
References
Ba, L., Wang, D., Hodgkinson, K. C., & Xiao, N. (2006). Competitive relationships between two contrasting but coexisting grasses. Plant Ecology, 183(1), 19-26. doi: 10.1007/s11258-005-9002-6
Clarkson, B. R., Smale, M. C., Williams, P. A., Wiser, S. K., & Buxton, R. P. (2011). Drainage, soil fertility and fire frequency determine composition and structure of gumland heaths in Northern New Zealand. New Zealand Journal of Ecology, 35(1), 96-113.
Cleveland, C. C., Townsend, A. R., Taylor, P., Alvarez-Clare, S., Bustamante, M. M. C., Chuyong, G., . . . Wieder, W. R. (2011). Relationships among net primary productivity, nutrients and climate in tropical rain forest: A pan-tropical analysis. Ecology Letters, 14(9), 939-947. doi: 10.1111/j.1461-0248.2011.01658.x
Eiserhardt, W. L., Svenning, J. C., Kissling, W. D., & Balslev, H. (2011). Geographical ecology of the palms (Arecaceae): Determinants of diversity and distributions across spatial scales. Annals of Botany, 108(8), 1391-1416. doi: 10.1093/aob/mcr146
Gehring, C. A., & Connell, J. H. (2006). Arbuscular mycorrhizal fungi in the tree seedlings of two Australian rain forests: Occurrence, colonization, and relationships with plant performance. Mycorrhiza, 16(2), 89-98. doi: 10.1007/s00572-005-0018-5
Gleason, S. M., Read, J., Ares, A., & Metcalfe, D. J. (2009). Phosphorus economics of tropical rainforest species and stands across soil contrasts in Queensland, Australia: Understanding the effects of soil specialization and trait plasticity. Functional Ecology, 23(6), 1157-1166. doi: 10.1111/j.1365-2435.2009.01575.x
Gleason, S. M., Read, J., Ares, A., & Metcalfe, D. J. (2010). Species-soil associations, disturbance, and nutrient cycling in an Australian tropical rainforest. Oecologia, 162(4), 1047-1058. doi: 10.1007/s00442-009-1527-2
Herrera, B., & Finegan, B. (1997). Substrate conditions, foliar nutrients and the distributions of two canopy tree species in a Costa Rican secondary rain forest. Plant and Soil, 191(2), 259-267. doi: 10.1023/a:1004209915530
Laliberté, E., Grace, J. B., Huston, M. A., Lambers, H., Teste, F. P., Turner, B. L., & Wardle, D. A. (2013). How does pedogenesis drive plant diversity? Trends in Ecology and Evolution, 28(6), 331-340. doi: 10.1016/j.tree.2013.02.008
Lambers, H., Brundrett, M. C., Raven, J. A., & Hopper, S. D. (2011). Plant mineral nutrition in ancient landscapes: High plant species diversity on infertile soils is linked to functional diversity for nutritional strategies. Plant and Soil, 348(1-2), 7-27. doi: 10.1007/s11104-011-0977-6
Medinski, T. V., Mills, A. J., Esler, K. J., Schmiedel, U., & Jürgens, N. (2010). Do soil properties constrain species richness? Insights from boundary line analysis across several biomes in south western Africa. Journal of Arid Environments, 74(9), 1052-1060. doi: 10.1016/j.jaridenv.2010.03.004
Paoli, G. D., Curran, L. M., & Zak, D. R. (2005). Phosphorus efficiency of Bornean rain forest productivity: Evidence against the unimodal efficiency hypothesis. Ecology, 86(6), 1548-1561.
Penfold, G. C., & Lamb, D. (2002). A test of the hypothesis of ecological equivalence in an Australian subtropical rain forest. Journal of Tropical Ecology, 18(3), 327-352.
Prior, L. D., Grierson, P. F., McCaw, W. L., Tng, D. Y. P., Nichols, S. C., & Bowman, D. M. J. S. (2012). Variation in stem radial growth of the Australian conifer, Callitris columellaris, across the world’s driest and least fertile vegetated continent. Trees – Structure and Function, 26(4), 1169-1179. doi: 10.1007/s00468-012-0693-8
Richards, M. B., Stock, W. D., & Cowling, R. M. (1997). Soil nutrient dynamics and community boundaries in the fynbos vegetation of South Africa. Plant Ecology, 130(2), 143-153. doi: 10.1023/a:1009742225383
Sangha, K. K., Jalota, R. K., & Midmore, D. J. (2006). Litter production, decomposition and nutrient release in cleared and uncleared pasture systems of central Queensland, Australia. Journal of Tropical Ecology, 22(2), 177-189. doi: 10.1017/s0266467405003020
Specht, R. L., Batianoff, G. N., & Reeves, R. D. (2006). Vegetation structure and biodiversity along the eucalypt forest to rainforest continuum on the serpentinite soil catena in a subhumid area of Central Queensland, Australia. Austral Ecology, 31(3), 394-407. doi: 10.1111/j.1442-9993.2006.01628.x
Stock, W. D., & Verboom, G. A. (2012). Phylogenetic ecology of foliar N and P concentrations and N:P ratios across mediterranean-type ecosystems. Global Ecology and Biogeography, 21(12), 1147-1156. doi: 10.1111/j.1466-8238.2011.00752.x
Warman, L., Bradford, M. G., & Moles, A. T. (2013). A Broad Approach to Abrupt Boundaries: Looking Beyond the Boundary at Soil Attributes within and Across Tropical Vegetation Types. PLoS ONE, 8(4). doi: 10.1371/journal.pone.0060789
Wright, I. J., Westoby, M., & Reich, P. B. (2002). Convergence towards higher leaf mass per area in dry and nutrient-poor habitats has different consequences for leaf life span. Journal of Ecology, 90(3), 534-543. doi: 10.1046/j.1365-2745.2002.00689.x
Rationale
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.
Task
For the major assignment, you will produce a bibliographic essay exploring the above topic.
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