City Forester, Tim Buchanan, reports that the American Elm was once the most abundant tree species in Library Park. Elms lined the entire sidewalk along Oak Street and several more were located throughout the park but especially in the area where the historic cabins are now located.

Approximately 50 American elms in Library Park succumbed to Dutch Elm Disease in the mid to late 1970s. Dutch Elm disease was first reported in Fort Collins in 1973-1974.