Many land managers know firsthand the damage invasive species can do to natural resources, but no one knows exactly why these species are able to out-compete native plants.

This is not just a Kentucky problem, as invasive species are common throughout the world. A long-held theory, developed by biologists, hypothesizes that invasive plants are more numerous in introduced sites compared to their native, or home, range, because an ecological change occurs during their invasion that gives them an advantage over native plants. This theory is known as the abundance assumption.

An international team of scientists that included University of Kentucky College of Agriculture’s Rebecca McCulley tested the abundance assumption on 26 invasive plant species at 39 grassland locations on four continents. Their results found that most species (20 of 26) had similar or lower abundances at the introduced sites compared to their home range sites.

McCulley and her lab members contributed two sites to the study, a pasture at Spindletop Farm in Lexington and Hall’s Prairie, a restored native tallgrass prairie in Logan County.

Eight species from both sites were considered invasive and included in the study. For the most part, the invasive species from Kentucky fell in line with the international findings. However, two species from Spindletop, Kentucky bluegrass and plantain, were more common here than their native sites.