Plenary Session Abstract

Developing Control Strategies for Invasive Plants

Bernd Blossey
Department of Natural Resources
Cornell University

The invasion of non-indigenous plants is considered a primary threat to the integrity and function of ecosystems and to rare and endangered species. While parks, nature preserves and other natural areas are managed for the preservation of their native fauna, flora and natural processes, they are under increasing pressure by many invasive species, including aquatic and terrestrial plants. While we have accumulated evidence for negative impacts of non-indigenous species as a group, the full extent of changes in ecosystem processes and floral and faunal composition as a result of the increased abundance of a single non-indigenous species is often anecdotal. Management practices should favor the long-term sustainability and health of protected areas, which may be dramatically altered by the invasion of non-indigenous species. In the absence of quantitative evidence, the important question for natural resource managers is how much evidence for negative impacts is sufficient or necessary before undertaking control programs and whether preventive management, including eradication of newly arrived species and of small populations, can be justified.

Common sense, experience and theory predict that control of invasive species is most economical and successful when they occur in small populations. At low abundance, non-indigenous plants may have no or only minor detectable ecosystem impacts. Justification for controlling small populations can then only be based on principles of economy, feasibility and concerns over potential (but not presently realized, recognized or quantified) negative impacts of species. This approach has been strongly criticized by some when applied to purple loosestrife (Lythrum salicaria L.), a Eurasian wetland plant introduced to North America. The important question is how much evidence do we need to begin a control program, including the development of biological control? While recognizing the considerable need to collect and publish quantitative evidence for ecosystem impacts of non-indigenous species to guide management decisions, I submit that negative ecosystem impacts are likely greatly underestimated. I will discuss new findings about impacts, development and implementation of nationwide control programs (particularly biological control) that target aquatic plant species such as purple loosestrife and phragmites.

Proud Partners in the Watershed-Wide
Chesapeake Bay Invasive Species Workshop

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