The effect of exotic pasture development on floristic diversity in central Queensland, Australia (original) (raw)
Related papers
2006
Despite major land use changes, much of the ground-layer vegetation on the Northern Tablelands of New South Wales is still dominated by native grasses. The native grassy ecosystems of the region were studied to determine the impacts of grazing, fertilising and cultivation history on vascular plant species richness. Sampling was stratified on the basis of management. The incidence of all plant species in 30 m quadrats was recorded at 373 sites within a 60 km radius of Armidale. Sites with a history of cultivation were found not to contribute any additional native species to the total number of native species found in uncultivated sites. In sites with no history of cultivation or fertiliser, the never grazed and infrequently grazed sites had significantly higher native species richness than grazed sites. The combined effects of increasing grazing intensity and fertiliser inputs significantly reduced native species richness and increased exotic species richness.
Weeds are commonly considered a threat to biodiversity, yet interactions between native and exotic species in grasslands are poorly understood and reported results vary depending on the spatial scale of study, the factors controlled for and the response variables analysed. We tested whether weed presence and abundance is related to declines in biodiversity in Australian grasslands. We employed existing field data from 241 plots along a disturbance gradient and correlated species richness, cover and Shannon diversity for natives and exot-ics, controlling for seasonal rainfall, climatic gradients and nutrient status. We found no negative relationships in terms of emergent diversity metrics and occupation of space, indeed, many positive relationships were revealed. When split by land-use, differences were found along the disturbance gradient. In high-moderately disturbed grasslands associated with land-uses such as cropping and modified pastures, positive associations were enhanced. Tolerance and facilitation mechanisms may be involved, such as complementary roles through different life history strategies: the exotic flora was dominated mainly by annual grasses and herbs whereas the native flora represented more diverse growth-forms with a higher proportion of perennials. The positive relationships existing between native and exotic plant species in high-moderately disturbed grasslands of South Australia are most likely due to facilitation through different strategies in occupation of space given that the effect of habitat suitability was controlled for by including environmental and disturbance factors. Consequently, although particular weeds may negatively impact biodiversity, this cannot be generalised and management focusing on general weed eradication in grasslands might be ineffectual.