Vegetation Patterns across the Sydney Basin during the Last Glacial Maximum based on Plant Biogeography, Ecology, Geomorphology and Climate

Despite the importance of the Last Glacial Maximum (LGM) in the formation of modern Australian vegetation, no comprehensive account exists of the likely vegetation of this period in the Sydney Basin. Likely past LGM vegetation events and patterns for this region are proposed, based on geomorphological, palynological and archaeological studies, combined with current geographical distributions of endemic, restricted and common plant species, inferences from basic ecological characteristics, observed vegetation community interactions, and morphological or genomic variation. Based on ecological attributes (stress-tolerators, competitors, ruderals), and geographic distributions, individual species are associated with likely past survival during the drier and colder LGM climate (28 000-18 000 years BP), across the different landscapes within the region. These include the old, climatically buffered, infertile (OCBIL) Sydney sandstone plateau systems; the old but more fertile shale (OCFEL) areas (Illawarra, western Sydney, Central Tablelands); the younger fertile alluvial lowlands (YODFELs); and the now-inundated LGM continental shelf/coastal plain. Potential LGM vegetation scenarios include Blue Mountains moisture-related stress-tolerant heath, mallee, seepage and cliffline vegetation on an LGM subalpine zone (>800 m elev.) with snowmelt and effectively better moisture; dry grassland and mallee shrubland on the Central Tablelands and western Sydney shale areas; and eastward movement of western clay soil species through Hunter Valley/Southern Highland connections and sclerophyll shrubs across mid-elevation dry sandstone. The importance of the coastal plain/continental shelf, including coastal wallum vegetation, is suggested as the origin of many species' distribution disjunctions. By interweaving circumstantial evidence and speculation, hypotheses and narratives can be developed to provide a spur to plant ecological and biogeographic research and advance research in the field. Manuscript received 30 May 2023, accepted for publication 6 December 2023