Floristic response to urbanization: Filtering of the bioregional flora in Indianapolis, Indiana, USA.

PREMISE OF THE STUDY: Globally, urban plant populations are becoming increasingly important, as these plants play a vital role in ameliorating effects of ecosystem disturbance and climate change. Urban environments act as filters to bioregional flora, presenting survival challenges to spontaneous plants. Yet, because of the paucity of inventory data on plants in landscapes both before and after urbanization, few studies have directly investigated this effect of urbanization.

METHODS: We used historical, contemporary, and regional plant species inventories for Indianapolis, Indiana USA to evaluate how urbanization filters the bioregional flora based on species diversity, functional traits, and phylogenetic community structure.

KEY RESULTS: Approximately 60% of the current regional flora was represented in the Indianapolis flora, both historically and presently. Native species that survived over time were significantly different in growth form, life form, and dispersal and pollination modes than those that were extirpated. Phylogenetically, the historical flora represented a random sample of the regional flora, while the current urban flora represented a nonrandom sample. Both graminoid habit and abiotic pollination are significantly more phylogenetically conserved than expected.

CONCLUSIONS: Our results likely reflect the shift from agricultural cover to built environment, coupled with the influence of human preference, in shaping the current urban flora of Indianapolis. Based on our analyses, the urban environment of Indianapolis does filter the bioregional species pool. To the extent that these filters are shared by other cities and operate similarly, we may see increasingly homogenized urban floras across regions, with concurrent loss of evolutionary information.