Plant traits and local extinctions in natural grasslands along an urban-rural gradient

1 The effect that the surrounding landscape matrix has on the loss of species from fragmented patches remains largely unknown. To determine whether there were differences in the persistence of plants inhabiting remnant patches in contrasting landscape types we examined the local extinction of grassland plants along an urban-rural gradient in western Victoria, Australia. 2 Thirty small grassland remnants that had been comprehensively surveyed between 1979 and 1990 were intensively re-surveyed. A total of 289 (26%) of the 1104 plant populations present in the 1980s were not relocated and were presumed to be locally extinct. The proportion of populations lost differed along the gradient, with higher local extinction rates at patches in urban (37%) and peri-urban landscapes (27%) than those in the rural landscape (20%). 3 We calculated the probability of local extinction of species in urban, peri-urban and rural landscapes using Bayesian logistic regression models. Across all plant functional traits examined, species had a consistently higher probability of local extinction in the urban landscape. 4 Species that were geophytes or hemicryptophytes with a flat rosette and species with seeds dispersed by wind or ants had substantially increased risks of extinction in the urban landscape. Low seed mass, the lack of vegetative reproduction and the presence of a soil-stored seed bank increased the probability of local extinction in all landscapes. Regionally rare species had a higher probability of local extinction in rural and peri-urban landscapes but rarity had little influence on extinction risk in urban landscapes. 5 Urbanization has a strong influence on the species composition of urban grasslands and substantially increases the probability of local extinction of plants with particular combinations of functional traits.