A functional group analysis of change in the abundance and distribution of 207 plant species across 115 years in north-central North America

Identifying declining species is essential for conservation planning. This research assessed abundance and distribution changes of 207 plant species in north-central North America and evaluated the importance of a suite of functional characteristics in predicting their persistence over 115 years (1895-2009). Functional characteristics included native versus introduced origin, pollination syndrome, symbiosis and habitat requirements, and phenological responsiveness to temperature change. Plant specimens from Ohio State University's Herbarium were used to assess abundance and distribution changes. The partial Solow equation and the sighting rate model were used to calculate the average probability that a species had declined over the study interval. Rarefaction analysis was used to calculate the percent change in distribution as measured by county occurrences from historic (1895-1970) to modern (1971-2009) time periods. Twenty-seven percent of the 207 species decreased in abundance from 1895 to 2009 and 68 % showed distribution contraction. Native species were seven times more likely to decline in abundance and showed a two-fold greater distribution contraction compared to introduced species. Introduced species that strongly advanced flowering with warming showed greater distribution expansion than those with weak phenological responsiveness. Species that require a symbiont for growth or development were twice as likely to decrease in abundance as those without symbiont requirements. This analysis indicates non-random patterns of threat to species diversity among plant functional groups. With climate warming, highly responsive introduced species may become more widespread. Thus, climate warming may exacerbate the already substantial impacts of land-use change, symbiont loss, and non-native species invasion on species persistence.