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AimWe examined patterns of rarity in the flora of a semi-arid mountain range with a high concentration of rare species and 150years of elevated grazing pressure, to establish the influences of habitat specialization, species biology, biogeography and grazing pressure in determining the distributions and abundances of species.

LocationGrey Range and associated Tertiary sandstone ranges, eastern semi-arid Australia.

MethodsWe characterized the major habitats by soil and vegetation parameters, and surveyed 647 sites across seven habitat units to determine the probability of occurrence of 19 rare species. We then analysed the occurrence of rare plants in relation to species biology (dispersal characteristics, flowering, fruiting and recruitment frequency), grazing pressure and, for the barren plateaux, their size and isolation.

ResultsRare species were found to be concentrated in three restricted habitat types - barren plateaux, gidgee toeslopes and sheltered habitats - which are clearly separated from other habitats in land-form, soil properties and floristics. Larger barren plateaux were more likely to harbour rare species, but there was no correlation between plateau isolation and the incidence of rare plants. No species seemed to be limited by low seed production, but barren-plateau shrubs recruited only infrequently. Only two species were adapted to long-distance dispersal, meaning that most are effectively stranded in their insular habitats. Although five perennial shrub species were heavily grazed, there were no significant relationships between the distance to water and the occurrence of rare plants.

Main conclusionsHabitat specialization, reproductive biology and biogeographical history interact to create the observed patterns of rarity in this semi-arid mountain range. There is no evidence that any species have become rare or restricted as a result of grazing pressure. Species confined to plateaux, sheltered habitats and gidgee toeslopes represent relictual populations, and the association of rare plants with larger plateaux suggests that local extinctions were more likely on smaller plateaux during Pleistocene climatic fluctuations.