Australian vegetation during the Tertiary: Macrofossil evidence

Abstract

The Australian Tertiary plant macrofossil record, although very incomplete, offers a unique insight into past vegetation composition and dynamics, and the effect of changing climate both on vegetation composition and plant evolution. During the Early Tertiary, southeastern Australia supported complex rainforests with a very high diversity of woody plant species. The prevailing climate included a moderate mean annual temperature and, more importantly, very little temperature variability away from the mean. As well as this, rain fall was high throughout the year, and humidity was also very high. There is no extant analogue either for this climate or for the vegetation it supported. As the climate cooled and temperature extremes developed, and rainfall declined and became more seasonal, rainforests in southeastern Australia declined in species numbers. Many taxa became extinct or migrated (or were restricted in range) northwards into the mid-high elevation equatorial rainforests where they, or their descendants, still occur. Some rainforest taxa evolved in response to the changing climate in southeastern Australia, although many of these were ultimately unsuccessful and became extinct in the region. As the climate further deteriorated, non-rainforest vegetation expanded in the drier and colder areas, although many of the taxa present in these expanding ecosystems may have had their origin in nutrient-poor rainforests.