A Late Holocene Vegetation and Environment Record from Byenup Lagoon,South-western Australia

South-western Australia has a Mediterranean-type climate and its infertile soils support a highly diverse angiosperm flora. Little is known of the vegetation history of this region, and this means that little can be said of the roles of environmental stability, climate change, or human impact on the maintenance or development of the high biodiversity of the region. This study presents a pollen and fossil charcoal record from two peat profiles from a freshwater lagoon region near Lake Muir, east of Manjimup, in south-western Australia. The record shows a glimpse of an early Holocene where a mix of Casuarina and eucalypts with an understorey of heath and some open herbaceous vegetation, including chenopods, occurred. Fire was not an important factor at this time. The main record begins from about 4800 BP, and shows a vegetation mix of Corymbia calophylla and Eucalyptus marginata, with the latter becoming dominant by about 3500 BP. Corymbia calophylla again becomes prominent in the last few centuries. A heathy understorey is present throughout the last 4800 years, but was apparently less dense during phases when C. calophylla was more prominent. Melaleuca woodland has been the main vegetation type around the wetland areas and areas of inundation since the mid-Holocene. Major fire periods at Byenup, around 4200 BP and between about 3000 and 2000 BP, did not result in major vegetation changes. An analysis of cation content in the sediments suggests that weathering and erosion rates have been relatively stable throughout the record, but an increase in phosphorus and possibly organic matter in the surface layers suggests that agricultural practices have led to changes in the chemistry of sediments. It is hypothesised that an increase in effective precipitation about 4800 BP led to the initiation of the continuous part of the sediment record at Byenup. This increase most likely resulted from a more effective westerly wind stream. Changes since this time are more likely a result of changing fire regime and the interaction of species, rather than climate shifts.