The greening of western australian landscapes: The phanerozoic plant record

Abstract

Western Australian terrestrial foras frst appeared in the Middle Ordovician (c. 460 Ma) and developed Gondwanan afnities in the Permian. During the Mesozoic, these foras transitioned to acquire a distinctly austral character in response to further changes in the continent’s palaeolatitude and its increasing isolation from other parts of Gondwana. This synthesis of landscape evolution is based on palaeobotanical and palynological evidence mostly assembled during the last 60 years. The composition of the plant communities and the structure of vegetation changed markedly through the Phanerozoic. The Middle Ordovician – Middle Devonian was characterised by diminutive vegetation in low-diversity communities. An increase in plant size is inferred from the Devonian record, particularly from that of the Late Devonian when a signifcant part of the fora was arborescent. Changes in plant growth-forms accompanied a major expansion of vegetation cover to episodically or permanently fooded lowland setings and, from the latest Mississippian onwards, to dry hinterland environments. Weter conditions during the Permian yielded waterlogged environments with complex swamp communities dominated by Glossopteris. In response to the Permian–Triassic extinction event, a transitional vegetation characterised by herbaceous lycopsids became dominant but was largely replaced by the Middle Triassic with seed ferns and shrubs or trees atributed to Dicroidium. Another foristic turnover at the Triassic–Jurassic boundary introduced precursors of Australia’s modern vegetation and other southern hemisphere regions. Most importantly, fowering plants gained ascendancy during the Late Cretaceous. Characteristics of the state’s modern vegetation, such as sclerophylly and xeromorphy, arose during the Late Cretaceous and Paleogene. The vegetation progressively developed its present-day structure and composition in response to the increasing aridity during the Neogene–Quaternary. Show more