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By the time Robert Brown visited western Sydney (1802–1805), its vegetation was already beginning to be affected by settlers' activities. The Cumberland Plain Woodland that occurred on the clay soils has now been extensively cleared and long-term management of remnants for species conservation is of high priority. Robert Brown's collections in the area, together with descriptions by Atkinson, Cunningham and other writers, provide us with valuable information on the vegetation and its floristic composition. Supported by recent site monitoring at Mount Annan Botanic Garden at Campbelltown, we interpret this information in the light of current ecological knowledge and conclude that:
• Woodland structure is variable in the short term; therefore seeking to conserve structure exactly as described in the historical literature is not necessarily appropriate.
• While the historical literature provides evidence of the broad floristic composition of the Cumberland Plain area overall, it does not provide sufficient detail on individual sites; future management of specific sites must therefore be based on current data.
• The evidence suggests relatively few species have become extinct overall, possibly because many species appear to be relatively long-lived, and have mechanisms to survive drought, fire and grazing, though not soil alteration.
• Many species, however, are now distributed patchily in localised remnants and rare species are not clustered in a predictable way; species diversity is therefore likely to be lost if further clearing of remnants occurs.
During the past two centuries massive land use changes in Australia have altered fire regimes, changed hydrology, increased soil salinity and nutrient levels, and altered abundance and distributions of animals with which native plants interact. Such changes to plant habitats may induce changes in range of indigenous plant species. We need to consider very carefully how to treat native species that naturalise outside their previous ranges. The spread of Pittosporum undulatum in the Sydney region provides a case study for considering approaches to this question.