Nonnative species – also called alien, introduced, exotic, intrusive or invasive species – are a direct threat to many desert species, both plants and animals.
In the next century, the greatest threat to our native plants and the wildlife species that depend upon them may well come from other plants. Thousands of plant species have been brought to North America in the past three centuries. Most are well-behaved, rarely penetrating natural areas. Several hundred, however, have no natural controls here, and are able to out-compete and gradually displace our native plants, even deep in forests and undisturbed ecosystems.
Some of these plants were brought here intentionally, for their medicinal, ornamental, or food value. Others hid in soil, crop seed, or ballast. Most came from other continents, but a few have spread from other parts of the US. In each region, different species are better adapted and therefore pose a greater threat.