Hilary Callahan headshot


On August 2, 2021, Hilary Callahan, professor of biological sciences, published new research in the journal Urban Ecosystems, titled “Seasonal patterns of native plant cover and leaf trait variation on New York City green roofs.” Alongside her co-authors, Kevin L. Griffin, Matthew I. Palmer, Sojin Lee, and Eric G. Yee, Professor Callahan evaluated green roof performance. Lead author Eric Lee, now a doctoral student researcher at Johns Hopkins University, earned a master’s degree in Conservation Biology at Columbia University in 2016 and served as a laboratory associate at Barnard between 2016 and 2017. 

Their study investigates the variation of abundance and leaf traits in plant species found on four different New York City green roofs during the 2015 growing season. The researchers determined that three major plant families (Asteraceae, Lamiaceae, and Poaceae) were the most present during this growing season and spanned the largest growth of green cover. Their investigations also showed that leaf traits were significantly affected by the growing season.  By ranking planted and spontaneous species in accordance to both cover and functional trait values, Professor Callahan and her co-authors were able to identify 11 species suitable for New York City green roofs