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ENV510 Landscape Ecology and GIS
Kellerberrin
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Vegetation with a grass dominated ground layer was sampled between October 1990 and March 1991. Data was collected in the form of presence/absence records for all higher plants in the 120 quadrats (which were 16m x 5m in area).
A disturbance rating was made for grazing, soil disturbance and water enrichment (ie where sites are receiving extra water from run-off) at each site. Ratings were based on physical evidence at the site, that is factors like irregularities on the surface, defoliation, dung and animal presence.
An ordination approach was used for analysis. This took the form of Canonical Correspondence Analysis (Hill, 1974).
The results showed that lithology accounted for most of the intersite variability in species composition and that soil disturbance was the most important disturbance factor. Grazing and water addition seemed to have a lower contribution, while a combination of soil disturbance and grazing had the greatest impact on floristic composition (McIntyre and Lavorel, 1994).
Richness was found not to vary singly in relation to environmental factors such as lithology, altitude and slope, but was affected by disturbance.
Reduced species richness occurred with increased soil disturbance and water enrichment, and under severe grazing intensity.
Environment and disturbance factors explaining floristic variability were lithology, altitude and soil disturbance. These factors had the strongest influence. While slope position, grazing and water loss was found to be less important.
Prior to European settlement, the occurrence of native species would have reflected ecological specialisation to environmental factors and effects associated with endogenous disturbances such as fire. This study suggests that the original vegetation patterns still remain, but these underlie the effects of impacts of exogenous disturbance regimes and exotic species.
Grassland communities are highly variable in space and time because of the role of chance in determining the composition. Combining distribution and environmental factors accounts for about 32% of the total variation for vegetation. This means that chance may contribute to a proportion of the unexplained variation, but also important may be factors like nutritional status, and details of grazing and soil disturbance in the past (McIntyre and Lavorel, 1994).
This study revealed that severe stock grazing, human induced soil disturbance and water enrichment were all causing a decline of native species and increased richness of exotic species in this area. In comparison, where conditions of moderate grazing could be found, higher native species richness was recorded.
A decline in rare species richness in heavily grazed sites, compared with less of a decline in lightly grazed sites, can be attributed to strong relationships between human modification of habitats and the decline of native and rare species richness. Native and rare species richness can therefore be seen to be an appropriate measure of conservation status for grassy communities in the region (McIntyre and Barrett, 1992).
The results of this study are a reflection of general trends that have been observed in Australian rangeland landscapes.
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