NatureServe Invasive Species Impact Rank (I-Rank)

Which non-native species pose the most serious threats to native species and ecosystems? To answer this question, NatureServe, in collaboration with The Nature Conservancy and the U.S. National Park Service, has developed a protocol for assessing and categorizing non-native plants according to their impacts on native biodiversity. The protocol is designed to focus specifically on the effects non-native species have on native plants, animals, and natural communities and to make the process of assessing non-native species objective, transparent, and systematic. It is intended to be applied to species as they occur over large areas, such as nations, ecoregions, provinces, or states.

The protocol is used to assess species individually for a specified region and to assign each an Invasive Species Impact Rank (I-Rank) of High, Medium, Low, or Insignificant to categorize its negative impact on natural biodiversity within that region. The protocol includes 20 questions grouped into four sections: Ecological Impact, Current Distribution and Abundance, Trend in Distribution and Abundance, and Management Difficulty. Each species is assessed by considering these questions, with the answers used to calculate a subrank for each of the four sections. An overall I-Rank is then calculated from the subranks. Text comments and citations to information sources are required to document the answers selected.

While designed for use in a specified contiguous, biogeographically diverse region, the protocol can be adapted to specified noncontiguous regions (such as the 50 U.S. states). NatureServe is now using the protocol to assess the non-native vascular plants that have established outside of cultivation in the United States.