NPS

Zebra mussels (Dreissena polymorpha) in nearby Lake Mead

Nonnatives, or exotics, are species that have been intentionally or unintentionally introduced to an area outside of their native range as a result of human activity. These species are not natural parts of our ecological communities, which includes plants and animals. Native ecological communities have evolved together over time as species adapted to new pressures and natural processes. Some species became extinct or extirpated (locally extinct) while others colonized the communities. As these changes took place, the original community was lost over time. This process is slow, but can be accelerated by fire, flood, and sudden climate change.

The introduction of nonnative species can disrupt the native ecological community which has developed over time. Because nonnative species are not a natural part of our ecological systems, they have not evolved with native species and lack natural checks on their populations, such as predators, competitors, and parasites. Nonnatives are typically adaptable and tolerant to a wide variety of conditions and are able to take over an area, sometimes forming a monoculture (an area dominated by a single species). Though some nonnative plants do not reproduce without human help (e.g., crops and ornamental plants), some spread very quickly and aggressively. Nonnatives can replace native species, which degrades the integrity and diversity of an area. These species disrupt the complex native ecological communities and the natural evolution of those communities, degrading native habitats and polluting gene pools by hybridization. The presences of nonnative species can also alter fire, water, nutrient cycles, and food chains.

NPS

Ravennagrass (Saccharum ravennae) removal

Many nonnative species have been introduced unintentionally, but some are introduced purposefully. Chukar (Alectoris chukar), a Eurasian exotic, was introduced to the Southwest in the 1940s as a familiar game bird for new immigrants. Nonnative fish have been introduced to many bodies of water for sport fishing, often outcompeting native fish. Nonnative plants such as tamarisk (salt cedar, Tamarix chinensis) and Russian olive (Elaeagnus angustifolia) were introduced to prevent soil erosion and as ornamental plants. They are now widespread and often severely degrade the ecosystems they invade. Plants can also be accidently introduced by “hitchhiker” seeds that get caught on boots and cars. The European starling (Sturnus vulgaris) was introduced to Central Park in 1890 in hopes of establishing all of the birds mentioned in William Shakespeare’s work in the United States. The starling evicts native birds from their nests and is now found across the United States, including the developed areas of Glen Canyon NRA. Nonnative species have also been intentionally introducing for industrial development and wildlife habitat enhancement.

Zebra mussels (Dreissena polymorpha), native to Eurasia, were accidently introduced to the U.S. in the ballast water of a ship. They have since spread from the Great Lakes to the much of the eastern U.S. and, more recently, across the Rocky Mountains to nearby Lake Mead, Lake Mohave, and Lake Havasu. Zebra mussels are typically spread by vessels that have been in an infested body of water and have not been allowed to completely dry or decontaminated before entering another body of water. These invasive mussels compete with native species and clog pipes. Zebra mussels are not known to be in Lake Powell, and a program is in place to prevent their spread to Lake Powell.

The National Park Service preserves natural ecological processes and native species. Nonnative invasive species threaten the resources preserved in Glen Canyon NRA. Glen Canyon controls eight invasive plant species through mechanical (e.g., cutting and pulling) and herbicidal treatments. Chemical herbicides that are not dangerous to humans or wildlife are often necessary to control or eradicate invasive plants, though controversial. Some plant species such as cheatgrass (Bromus tectorum) and Russian thistle (Salsola pestifer) are so well established and abundant that they are too difficult to control. Prevention programs such as the zebra mussel program at Glen Canyon NRA, aim to stop the spread of invasive species to Glen Canyon NRA. Increased awareness about invasive nonnative species can also help prevent the spread of these destructive species.

Published 8/07