Summary 1.As human populations increasingly live in cities, urban floras and the ecosystem services they provide are under increasing threat. Understanding the effects of urbanization on plants can help to predict future changes and identify ways to preserve biological diversity. Relatively few studies document changes through time in the flora of a focal region and those that do primarily address European floras. They often rely on contemporary spatial gradient studies as surrogates for changes with time. 2. We compare historical species records (prior to 1940) with the current flora for Marion County, Indiana, USA, home to Indianapolis, the 13th largest city in the United States. Specimens from the Friesner Herbarium of Butler University and other vouchered records for the county provided the basis for historical records. Current records are derived from inventories of 16 sites conducted by Herbarium staff and other botanists over the past 15 years. 3. Physiognomic group, wetland classification and nativity (native vs. non-native) were determined for each species. Fidelity to high-quality habitat was quantified using coefficients of conservatism (C-values). 4. The last 70 years have seen a significant turnover in species presence, most notably a decrease in native plant species number (2.4 per year) and quality, with an accompanying increase in non-native plants of 1.4 per year. Loss of species has been non-random, with a disproportionate number of high-quality wetland plants lost. The signature of past land use can be seen in physiognomic changes in the composition of the flora that reflect the shift from agriculture to urban ⁄ suburban land use. 5. Many invasive non-native shrubs now present have escaped from cultivation, highlighting the combined threats of habitat conversion and human plant preference to native flora in cities. These invasives likely present the greatest threat to remaining biodiversity. 6. Synthesis. This study demonstrates the value well-documented historical records, such as those housed in herbaria, can have in addressing current ecological issues.

Urban environments pose special challenges to flora, including altered disturbance regimes, habitat fragmentation, and increased opportunity for invasion by non-native species. In addition, urban natural area represents most people's contact with nature, given the majority of the world's population currently live in cities. We used coefficients of conservatism (C-values), a system that ranks species based on perceived fidelity to remnant native plant communities that retain ecological integrity, to quantify habitat quality of 14 sites covering 850 ha within the city of Indianapolis, Indiana, in the Midwestern United States. All sites contained significant natural area and were inventoried via intensive complete censuses throughout one or two growing seasons within the last 15 years. Mean C-values for five sites were high, especially when compared to values reported for the highest quality preserves in central Indiana. However, for most sites the difference in mean C-value with and without non-natives was rather high, meaning that natural quality is likely to have been compromised by the presence of non-natives. Sites receiving the highest levels of stewardship and those with the least public access via trails had the highest mean native C-values. A total of 34 invasive non-native species were found across all 14 sites. Most were woody species. Mean C-value over all sites was significantly negatively correlated with the number of non-natives present, especially those considered invasive. These results demonstrate for the Indianapolis area, and likely other urbanized OPEN ACCESSDiversity 2011, 4 612Midwestern cities, remnant natural areas can retain high ecological value, especially if they receive regular environmental stewardship.

ABSTRACT.-Peri-urban natural areas, at the boundaries of cities and adjacent agricultural/ rural land, are subject to ecological threats endemic to both land use types. We used permanent plots to document changes in habitat quality by monitoring herbaceous-layer plant species presence and cover over a decade (1996/97 and 2007) in two peri-urban nature preserves in central Indiana, U.S.A. The preserves are comprised of different forest community types: wet-mesic depressional forest and mesic upland forest. Habitat characteristics, based on Floristic Quality Assessment parameters, showed only a single change for either preserve between survey years: wetness values were lower in the wet-mesic depressional site in 2007 than in 1996, indicating more plants with affinity for wet soil. No changes in community structure (total species richness, evenness, and diversity) were found. The number of nonnative species increased between survey years, especially in the wet-mesic depressional forest, where numbers went from zero to six, five of which are classified as invasive. There was considerable turnover in individual species presence, with perennial forb species the most likely species to be found in only 1 y or the other. Species did not rearrange themselves within plots, but completely appeared or disappeared from all plots within a preserve between the sample years, suggesting that species composition of the flora is dynamic. Management recommendations, including those related to evidence of heavy deer browse, are presented based on our findings. Repeat monitoring of our plots in future decades will allow quantification of any extinction debt that may now be in place due to the increased presence of nonnative species, especially invasive shrubs escaped from landscaping.