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 abunda nce of 373 native plant species in Auckland, New Zealand, with the aim of i dentifying the attributes that predisposed some species to local extinction and rarity following European settlement. The 1871 survey records the rela tive abundance of native plants in the Auckland area just 31 years after Eu ropeans began clearing the native vegetation for settlement, whereas the 19 85 survey records the relative abundance of the same species 114 years late r, when the area had been transformed into an urban landscape. Four attribu tes 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 l ikely 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 monoco tyledons; and (4) species occupying habitats that suffered the greatest los s of area following European settlement were more likely to be extinct or r are in 1985 relative to species occupying less affected habitats. Two addit ional attributes, long-distance dispersal ability and capacity for clonal s pread, failed to independently explain significant variation in 1985 abunda nce. We discuss the likely causes of these relationships and consider their implications for understanding extinction processes.