Herbarium specimens reveal regional patterns of tallgrass prairie invasion and changing species abundance across 130 years

Matthew Austin, Andrew Kaul, Adam Smith, Matthew Rothendler, Richard Primack

The spread of non-native species is an acute threat to global biodiversity. However, a lack of long-term, spatially widespread occurrence data has prevented investigation of how multi-species invasions affect native assemblages. We harnessed more than 65,000 digitized herbarium specimens across 522 species to study how relative abundances of native and non-native species have changed since the 1890s in tallgrass prairies in three ecoregions of Missouri, USA. To validate specimen-based relative abundances against standardized field surveys, we compiled 65 paired field-herbarium datasets and tested whether native percent cover positively correlates with relative abundance of native specimens. Non-native species were more likely to have increased in the Interior Plain and Interior Highland ecoregions, while species that changed in abundance in the Atlantic Plain were more likely to have decreased regardless of native status. Native percent cover and relative abundance of native specimens were positively correlated and trends were robust to overall sample size through time. Our results support the use of herbarium specimens for investigating patterns of relative abundance shifts of native and non-native species. Specimen-based relative abundance shifts have scientific value for providing quick, taxonomically- and spatially-broad overviews of how non-native species have affected native assemblages, which can guide more precise, fine-scale investigations.