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

Invasive species are common throughout the world. A long-held theory developed by biologists hypothesizes that invasive plants are more numerous in introduced sites than in 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–called the Nutrient Network–that includes Rebecca McCulley, MS, PhD, a grassland agroecologist with the University of Kentucky College of Agriculture, tested the abundance assumption on 26 invasive plant species at 39 grassland locations on four continents. Their results were contradictory to the abundance assumption, indicating that most species (20 of 26) had similar or lower abundances at the introduced sites than at their home range sites.

McCulley and her lab members contributed two Kentucky 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, McCulley’s observations about the invasive species in Kentucky fell in line with the international findings. However, two species from Spindletop–Kentucky bluegrass and plantain–were more common there than at their native sites