The presence of invasive species typically reduces an ecosystem’s overall biodiversity. This is because they can displace native species, reduce food sources for wildlife, outcompete native vegetation for resources, etc. Invasive species can also alter disturbance regimes, which can increase the decline of other native species. For example, the introduction of cheatgrass (Bromus tectorum) increases the frequency of fire regimes, making it difficult for native vegetation to regenerate adequately between wildfires. Also, the introduction of diseases and disturbance agents, such as the fungi that cause Dutch elm disease (Ophiostoma ulmi and Ceratocystis ulmi), could result in widespread mortality of many native species. When invasive species are established, it is difficult and costly to control them, and eradication is often impossible.
Amy Grotta, Assistant Professor and Cooperative Extension Forester, Oregon State University
