The influence of Eucalyptus globulus Labill. on the environment and vascular plants in a Tasmanian grassy woodland

The aims of this thesis are to document and explain heterogeneity creating processes associated with the presence of Eucalyptus globulus in a fire-prone grassy woodland ecosystem, with the research hypotheses being that: (1) Eucalyptus globulus creates environmental heterogeneity; (2) this induced environmental heterogeneity is reflected in the species richness of the woodland. Log shadows, linear bare patches, assumed to be the location of burnt fallen logs of Eucalyptus globulus, seemed best explained by soil moisture. In comparison to adjacent ground with dense grass cover, the log shadows had: low microbial activity, low N, low SOM, more sand, less silt, less clay and higher infiltration rates. Log shadows parallel to the contours had different patterns to those orthogonal to the contours. Tree diameter influences floristic composition close to the tree. For plots located immediate to the tree, ordination scores were strongly separated by tree diameter class. The separation became less obvious when the plots were further from the tree base. Soil available phosphorus and nitrogen did not vary by position in relation to the tree. Organic matter content and particle size in the soils near the tree base is affected by tree size. The highest organic matter and sand contents are found next to the small trees. Soils on the up side of the trunk were more level than soils on other sides. Rock cover was higher in the down side of the trunk than the up side. Rock cover significantly increased with tree size. The accumulated leaf litterfall under the canopy and in the open was not significantly different by the end of the year. The annual bud and flower litterfall under the canopy of Eucalyptus globulus was significantly higher than in the open. Annual fruit litterfall was also significantly greater under the canopy. Significant differences in bark litterfall between under the canopy and the open occur only in November, December and March. Branch litterfall under the canopy was higher than in the open with exception of March. Annual litterfall of possum droppings was also significantly greater under trees. The majority of nutrients originated from the leaf litter, although most of litter mass comes from bark. Wildlife may be an important component in the cycle of nutrients in the Eucalyptus globulus dominated woodlands. In addition to the rapid decay of possum dropping, the average monthly nutrient contents in possum droppings were remarkably higher than other litter materials. Most of the litterfall occurred under the canopy. If the same amount of litterfall occurred in the open, the release of nutrients from the litter into the system might become much greater since the rates of decomposition of all types of litter were lower under the canopy. These slow rates might relate to low soil moisture content under the canopy.