An important environmental factor affecting the Niobrara National Scenic River valley is the presence of several exotic plant species including purple loosestrife, leafy spurge, Canada thistle, and spotted knapweed. Currently, The Nature Conservancy has integrated a biological control program on the Niobrara Valley Preserve (TNC owns approximately 25 miles of riverfront property in the Scenic River corridor) by releasing Galerucella spp. beetles to control loosestrife. Additionally, the University of Nebraska-Lincoln has an experimental plot on the Preserve where researchers are examining the effects of different tilling and mowing regimes on purple loosestrife.
Each summer the Northern Great Plains Exotic Plant Management Team visits the Niobrara NSR to spray noxious weeds and map treated acres. The NPS also works within the Middle Niobrara Weed Awareness Group (MNWAG) to encourage and assist private landowners in controlling noxious weeds. Both land (ATV and backpack) and aerial spraying have been utilized in controlling purple loosestrife, Canada thistle and leafy spurge. The NPS hopes to begin spraying with local park staff in 2008 to better control invasive species.