Changes in the Abundance and Diversity of Proteaceae in South‐western Australia: a Review of an Integrated Palaeoenvironmental Study

Abstract

South-western Australia is a globally significant hotspot of Proteaceae diversity. This review reports on changes in the abundance and diversity of Proteaceae in south-western Australia. Using palynology, the data were obtained from three sediment sequences from the Eocene, Pliocene and Holocene, as well as a modern pollen rain study, in the context of a vegetation history framework. The total percentages of Proteaceae pollen in pollen counts indicate that the number of Proteaceae in the vegetation are highest at present, slightly lower, yet still high in the Eocene, reduced by the Pliocene and lowest in the Holocene. It was found that Proteaceous genera can contribute up to 50% of the total modern pollen rain. Sediment from Lake Lefroy showed Nothofagus-dominated rainforest occurred in the Middle to Late Eocene. Proteaceae species were at least as diverse as today, contributing up to a maximum of 42% of the total pollen rain, and varying across small lateral distances. A laminated Pliocene age sequence from Yallalie confirmed other studies that south-western Australia was covered by a rich vegetation mosaic consisting of heath and wet rainforest elements. Proteaceae species were a consistent component of the counts, although diversity and abundance (maximum 5%) were low. A Holocene record from Two Mile Lake, near the Stirling Range, recorded little environmental change. Proteaceae species were noted in low abundance, at a maximum of 3.5% of the total pollen count. It is likely that both changing pollination mechanisms and changes in associated vegetation are important in determining the dispersal of Proteaceous pollen.

Fire-adapted Gondwanan Angiosperm floras evolved in the Cretaceous

“…Atmospheric oxygen levels were up to 15% higher than currently and burn probability was the highest for the last 60 My (Figure  3). Further, deeply weathered sands or siliceous/lateritic rocks, often in open, well-drained parts of the landscape, were widespread and would have provided ideal refugia for the sclerophylls, especially Proteaceae, in their own communities [38,40-42]. Indeed, the Proteaceae ( Banksia -like wood, pollen akin to Petrophile , Adenanthos ) at Lake Lefroy, SWA in the mid-Eocene accounted for 34% of all pollen (when Nothogfagus was omitted), with species richness values comparable with those in SWA scrub-heath today [42].…”

“…Further, deeply weathered sands or siliceous/lateritic rocks, often in open, well-drained parts of the landscape, were widespread and would have provided ideal refugia for the sclerophylls, especially Proteaceae, in their own communities [38,40-42]. Indeed, the Proteaceae ( Banksia -like wood, pollen akin to Petrophile , Adenanthos ) at Lake Lefroy, SWA in the mid-Eocene accounted for 34% of all pollen (when Nothogfagus was omitted), with species richness values comparable with those in SWA scrub-heath today [42]. Interestingly, where fire did occur around the eastern Otway Basin, it not only led to a severe reduction in Nothofagus but also in Proteaceae and Myrtaceae [43], implying that the species there were more vulnerable to fire than their western counterparts [42].…”