Corydalis incisa: A new non-native herb is spreading through an urbanized riparian watershed in NY and negatively impacting native spring ephemerals

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Christina Andruk, Biology, Iona College, New Rochelle, NY and Suzanne Nolan, Director, Bronx River Parkway Reservation Conservancy, New Rochelle, NY

Background/Question/Methods
Corydalis incisa (Incised Fumewort) is an annual to biennial herb that is native to Asia. It was prioritized for early detection and rapid response by the NYDEC and USDA. Populations have been detected in riparian habitat throughout the Mid-Atlantic. The objectives of this study were to a) document the distribution of C. incisa in 2017 and 2020 along the Bronx River in NY, b) assess its relationship with native and other non-native species, and c) report on effectiveness of two control methods. We established ninety 1-m2 plots in C. incisa populations along the Bronx River in the Bronx River Parkway Reservation in Westchester County NY in spring 2017. Plots were randomly assigned to be pulled, clipped, or left as control (N=30). We recorded percent cover of all vascular species and counted the number of adult and juvenile C. incisa individuals in each plot in spring 2017-2019. We used a count model to assess the effect of treatment on the number of C. incisa individuals across the three years. We also analyzed the effect of C. incisa cover on native and non-native cover, species richness, and the cover of dominant native and non-native species.
Results/Conclusions
We include a map showing an increase in the geographic range of Corydalis incisa from 2017 to 2020 despite extensive control efforts both inside and outside plots. C. incisa was most often found in areas close to the river with high deposition that were not already invaded by the non-native Ficaria verna (Lesser celandine). Analysis of plot data and our personal observations have demonstrated the difficulty in studying this species in a highly dynamic riparian system. Corydalis incisa was often absent from our permanent plots, even though it was still present in the area surrounding the plots. Even so, we were able to conclude that simply clipping individuals was not sufficient to control populations and that pulling was more effective. Plot data indicated a significant negative relationship between C. incisa cover and the cover of native spring ephemerals Claytonia virginica (Spring beauty) and Asarum canadense (wild ginger). This is likely due to high trait similarity between C. incisa and many native wildflowers which are also are myrmecochorous spring ephemerals. This highly urbanized system still has some native understory which warrants protection so that the public can continue to have access to this historic resource.