A method for evaluating the potential ecological impact of invasive species

Researchers have developed and tested a new method for evaluating the potential ecological impact of the invasive species at a site. Their approach, called the Index of Alien Impact - is innovative for a couple of reasons.

First, the method goes beyond the conventional approach of just measuring how common invasive species are at a site, and in addition, assesses their specific qualities of invasiveness (e.g. the extent to which they alter the ecosystem, their ability to grow in different conditions, their dispersal mechanism etc). More traditional approaches, by focusing on metrics like abundance that describe the current extent of invasion, may miss out on certain warning signs for future problems.

Second, the method takes a cumulative approach in which it calculates a combined invasive impact score for an entire site based on the individual scores of all the exotic species present. Compared to conventional approaches that just look at individual species, this cumulative metric can give resource managers a better perspective for restoration planning and monitoring.

Teresa Magee and fellow researchers tested the approach on streamside vegetation along 35 reaches in Eastern Oregon. Their findings published in the journal Environmental Management illustrate some of the advantages of their method compared to more traditional approaches.

Certain areas scored highly on the Index of Alien Impact even though the relative cover of invasive species was low. This signals that these areas could be in the early stages of a problematic invasion. Metrics looking only at invasive species cover might miss these warning signs.

They also found that the alien index scores varied widely across certain sites and were greater in certain vegetation communities than others. Comparing scores across areas can allow restoration planners to prioritize efforts.

Furthermore, the method had advantages for monitoring restoration success. For example, restoration efforts that target one invasive plant may achieve eradication giving the impression of success even though other exotic species have moved into its place. By taking a cumulative approach, the index of alien impact is better able to catch these types of problems.

While the researchers tested the method on streamside habitat in Oregon, they note that the approach is potentially applicable to any location. In different areas, one would have to adjust the criteria used for evaluating species to better reflect the local conditions that affect invasion.

Similar to all research published in Environmental Management, this study gives an extremely thorough methodology of how to develop and implement the Index of Alien Impact in a given location. For those interested in the approach, I highly recommend you check it out.

--Reviewed by Rob Goldstein

Magee, T., Ringold, P., Bollman, M., & Ernst, T. (2010). Index of Alien Impact: A Method for Evaluating Potential Ecological Impact of Alien Plant Species Environmental Management DOI: 10.1007/s00267-010-9426-1