Determinants of plant extinction and rarity 145 years after European settlement of Auckland, New Zealand

We analyze a 114-year historical record (1871–1985) of the change in abundance of 373 native plant species in Auckland, New Zealand, with the aim of identifying the attributes that predisposed some species to local extinction and rarity following European settlement. The 1871 survey records the relative abundance of native plants in the Auckland area just 31 years after Europeans began clearing the native vegetation for settlement, whereas the 1985 survey records the relative abundance of the same species 114 years later, when the area had been transformed into an urban landscape. Four attributes were significantly and independently related to the probability that a species was locally extinct or rare in 1985: (1) compared with species that were common in 1871, initially rare species were more likely to be extinct or rare in 1985; (2) compared with tall species, short species were more likely to be extinct or rare in 1985; (3) gymnosperms and dicotyledons were more likely to be extinct or rare in 1985 than were pteridophytes or monocotyledons; and (4) species occupying habitats that suffered the greatest loss of area following European settlement were more likely to be extinct or rare in 1985 relative to species occupying less affected habitats. Two additional attributes, long-distance dispersal ability and capacity for clonal spread, failed to independently explain significant variation in 1985 abundance. We discuss the likely causes of these relationships and consider their implications for understanding extinction processes.