Fire-mediated effects of overstorey on plant species diversity and abundance in an eastern Australian health
2003
Tozer, M.G. | Bradstock, R.A.
Overstorey shrub species are known to influence the composition of the understorey in Southern Hemisphere heathlands. Overstorey densities are susceptible to variations in fire frequency; thus, fire regimes may influence overstorey/understorey interactions and overall floristic composition. We compared patches of Banksia heath which had supported an overstorey during a fire interval of about 30 y with patches where the overstorey was absent during the same period, and tested for differences in species composition as a function of overstorey presence. Floristic composition varied significantly between overstorey patches and open patches. Most species were less abundant in overstorey patches, however some were more abundant. The relative abundance of species in relation to overstorey was unrelated to their fire response, propagule longevity or propagule storage location. There was significantly less biomass in overstorey patches compared with open patches. The effect of the overstorey varied with soil moisture. In a dry area, the number of species was lower in overstorey patches, with fewer herb and shrub species present compared with open patches. Fewer species were recorded in a wetter area, but overstorey had no effect on the number of species recorded. Reduced intensity of competition among understorey species in overstorey patches could be responsible for the higher abundance of some species in these patches. We postulate that full diversity will be maintained when the density of overstorey shrubs fluctuates widely over a relatively short period of time. This is most likely when fire frequency is highly variable.
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