Control of invasive species, either directly or through broader management strategies like fire and grazing, take up more time than any other facet of the Nebraska program's land stewardship.
The USDA defines an invasive species as "non-native (or alien) to the ecosystem under consideration" and "whose introduction causes or is likely to cause economic or environmental harm to human health". According to Karie Decker, coordinator at the Nebraska Invasive Species Project, and Craig Allen, leader of the Nebraska Cooperative Fish and Wildlife Research Unit, there are approximately 500 established nonnative plants in Nebraska. It's the most commonly identified threat in Nebraska's Natural Legacy Plan.
For example, the biggest invaders in the eastern half of the state are exotic grasses like smooth brome, Kentucky bluegrass, and reed canarygrass because they can form dense monocultures and outcompete many other plant species. Once those grasses have become established and have reduced plant diversity, regaining that plant diversity requires massive restoration effort.
It is no surprise, then, that successfully controlling invasive species may be the most difficult (and important) part of prairie management, according to Eastern Nebraska Program Director Chris Helzer. "There are few things more frustrating than the realization that, despite your best efforts, there are more than there were the year before," he said.
Trees are a close second to non-native grasses, and problem trees include native species such as dogwood, sumac, honey locust, and eastern redcedar - and nonnative species like buckthorn, honeysuckle, Siberian elm, osage orange, and black locust. Trees are a major problem because they can transform the physical structure of natural habitats - in addition to decreasing plant diversity. They change grasslands into woodlands (eliminating most grassland wildlife and plant species) and open woodlands into dense woodlands that have much lower biological diversity.
The Conservancy has taken up the fight against invasives in several landscapes. On the Missouri River, the Conservancy is establishing high diversity restorations that are more resistant to invasive species and noxious weeds. We are keeping an eye on brome surrounding the lowland prairies of the saline wetlands. Fire and grazing management are integral parts of our stewardship efforts in the Platte and Niobrara River valleys. A major initiative on the Platte River is fighting phragmites.
Invasive species are a challenge to control and predict. "With invasive plants, the battle landscape is constantly changing," said Helzer. "We are still figuring it out."