Holocene vegetation change in the mediterranean-type climate regions of Australia

In Australia mediteranean-type climates occur in southwestern Australia and in near coastal South Australia and adjacent western Victoria. These regions support species-rich sclerophyllous heaths and shrublands with the biodiversity particularly high in the southwest. Palynological records show that around the timne of the Last Glacial Maximum the climate was sufficiently severe that the vegetation of the southeastem regions was of a different character compared to today with grasses and Asteraceae more common everywhere. In the southwest the differences between Last Glacial Maximum and the Holocene were less pronounced and the tree and shrub genera Casuarina and Allocasuiarina were more prominent, and heathland and shrubland remaining the main vegetation type. Most of the records from the Last Glacial Maximun verify that common taxa in mediterranean-type climate environments today were present through that period in low niumbers. The modem chairacter of the vegetation developed arounid two key periods: the Pleistocene/Holocene boundary, and, to a much smaller degree, from the mid-Holocene, with the chaniges somewhat less in the southwest. The mid-Holocene period was mnarked by slightly wetter and waimer conditionis than present across all of southeastem Australia, yet most palynological records show little if any response in terrestrial vegetation in relation to this climate. The most significant Holocene changes appear to be a gradual decline in the importance of Casuarina, and changes in the abundance of Corymbia calophylla in the southwest. Many of the palynological records also have fossil charcoal histories and it is clear that, while there has been some regional variation. fire has been an important environmental feature of the regions throughout the Holocene. However, there are few indications that fire had any major role in vegetation change. What is clear is that European settlement, from about 150-180 years ago, wrought the greatest changes on vegetation, and possibly because of the parallel climate and environmental conditions the main invasive species have come from other mediterranean-type climate regions.