Land managers may benefit from spending more time monitoring nonindigenous invasive plants to identify those that pose the greatest threat, according to an article in the January-March 2009 issue of Invasive Plant Science and Management.

The article, "The Rationale for Monitoring Invasive Plant Populations as a Crucial Step for Management," relates results from a model simulation of four plant management strategies. Authors Bruce D. Maxwell, Erik Lehnhoff, and Lisa J. Rew examine how land managers can best deal with invasive plants despite budget constraints and a lack of knowledge.

Most often, land managers rely on the "early detection rapid response" (EDRR) strategy, with little regard for the length of the plant invasion or its potential to multiply. "The EDRR strategy is logical and represents an economic optimum approach if detection and eradication possibilities are high," according to the authors.

But the researchers wanted to see if other methods would improve the eradication rate. Specifically, they used a simulation model to evaluate four plant management strategies over a 20-year period:

  • Managing a fixed number of populations at random each year (EDRR random).
  • Managing an equivalent number of populations along a road each year (EDRR road).
  • Managing half of the fixed populations that are determined to be sources of new populations (monitoring every year).
  • Managing an equivalent set of source populations only in even years, leaving the odd years for monitoring (monitoring every other year).

The simulation found that the EDRR that restricted management to roadsides was the least effective for reducing the number of plant populations, which is "disconcerting considering the prevalence of management restricted to roadsides," according to the authors. Currently, they write, "invasive species populations are treated primarily along roads without regard to their potential for further spread or stage of invasion," and that process may deserve re-evaluation.

According to the simulation, the two most effective strategies for reducing an increase in total plant populations were EDRR random and monitoring every year. But controlling them over time may require more specific measures.

"Critics of monitoring populations believe that the time and money taken for monitoring would be better spent directly on managing populations," according to the authors. However, "efficient evaluative techniques for identifying source populations could improve management of species that have recently arrived."

The simulation found that monitoring to identify source populations was effective when more than 10 plant types were present before management was started, because "the value in identifying source populations increased as the number of years of simulation was increased."

There may be a brief period when land managers can effectively treat invasive plant sources with EDRR, but the researchers say "invasions may rarely be detected early enough for EDRR to be the most effectively strategy for reducing the invasion rate into a management area."

They suggest further research on how to best monitor plant populations and identify their invasion or source potential.

"Land managers may be wise to adopt a new mantra: 'early detection, rapid monitoring, and thorough management,'" according to the authors.

To read the entire article, "The Rationale for Monitoring Invasive Plant Populations as a Crucial Step for Management (Vol. 2(1):1-9)," click here.