Impacts of key threatening processes on grass-dominated ecosystems in a high CO₂ world: a case study of Cumberland Plain woodland

Rising atmospheric CO₂ concentration is one of the best documented global changes of the past half century and may have a profound effect on the structure and functions of ecosystems globally. Grass-dominated ecosystems (hereon referred to as grasslands) may be particularly vulnerable to this increase in atmospheric CO₂ concentration due to their highly dynamic nature. Historically, the major threat to grasslands was their conversion to an agricultural landscape. Although this conversion continues today, grasslands face a number of other threatening processes whose impacts may be exacerbated by rising atmospheric CO₂ concentration. This thesis explores how these threatening processes interact with elevated CO₂ levels and each other to impact the structure and function of grasslands. Four threatening processes to grasslands that may be substantially modified under elevated CO₂ levels were identified and examined in this thesis. These threatening processes were extreme climatic events, exotic plant invasion, woody plant encroachment and changes to fire regime. Data for all chapters were obtained by carrying out manipulative CO₂ glasshouse experiments using Cumberland Plain Woodland, an open grassy woodland community of western Sydney, as the model grassland system. Chapter 2 and 4 test the vulnerability of grasslands to extreme drought and woody plant encroachment under elevated CO₂ levels. Chapter 3 investigates the interaction between extreme drought and elevated CO2 levels and how this may facilitate exotic plant invasion. Chapter 5 examines the changes in leaf flammability and fuel load accumulation of grassland species under elevated CO₂ levels.