Prioritizing Weeds

By Ron Hiebert

Which invasive species cause the most serious ecological threats? And, which are most amenable to management? With more than 100 alien plants on many wildland sites and the daunting prospect of long-term expensive management strategies, these are not academic questions. Many managers may be inclined to just throw up their hands and give up.

The alien plant ranking system (APRS) is an automated web-based resource that can help managers work through tough decisions about prioritizing the management of alien plants. APRS helps identify those species that have the most serious impact—those on site of limited distribution or off site with a high potential to invade, as well as those that appear innocuous (usually the majority). APRS also helps managers assess the feasibility of controlling the most threatening species.

The system guides managers through 25 questions in three sections relating to individual species: (1) current level of impact, (2) potential of a species to become a problem, and (3) feasibility of control. The sections include questions about the distribution and abundance of species, the number of seeds they produce, and their dispersal capabilities. There are also questions about whether a species is known to seriously impact other sites. When all the alien species known to occur on or adjacent to a site have been scored, the system ranks them according to current impact, potential impact, and feasibility of control.

Using the System

Step 1. List known and potential alien plants in the area. Good places to start include species lists and research reports, site-specific herbarium specimens, and a preliminary site survey. To determine which species are alien, each plant on the list should be checked against floras of the area.

Step 2. Survey the site. This more thorough site survey can be either a systematic walk through or a quantitative spatially-based sampling scheme such as a GIS-based survey. Though more expensive, GIS-based surveys show distribution and abundance information that can be correlated with disturbances, roads, and vegetation type, for example. GIS sampling schemes also can serve as the basis of invasive species monitoring programs.

Step 3. Search the literature. Managers will need to do a comprehensive literature search to answer the questions on the ecology, biology, and control methods for each alien species found. This is the most time-consuming step in the process. To help, the U.S. National Park Service has begun to front-end load data on alien species and prepare fact sheets for species already determined to be invasive.

Step 4. Fill out the data sheets. The system now has enough information to create graphs showing species scores and management status (Figure 1).

Step 5. Interpret the results. The final and most important step is to incorporate the outputs (listed below) in designing alien plant management strategies and action plans.

Considerations and Limitations

Although the APRS was initially designed to help make management decisions on individual sites, it has since been adapted for the State of Minnesotañand could be further adapted for use on a regional or even national scale. However, managers should bear in mind that results are good only for a limited space and time. Data should not be extrapolated from one site to another, nor should data be considered to reflect current conditions for a period of more than five years.

Another limitation of APRS is that many users have had difficulty responding with confidence to all questions. For some species, for example, seed longevity in the soil is not known; whether a species can be successfully controlled, what the side effects of control may be, or what the cost will be in time and dollars are other examples. Other users have had difficulty dealing with scale and heterogeneity issues. Alien species may be prominent in one location or community within a site and scattered or absent in others. Yet APRS asks for just one response. Lessons from use of the APRS in the Channel Islands National Park provide a good example of how to deal with this particular problem. As the distribution and abundance of alien species varied highly between islands, managers decided to rank species by island rather than for the entire park.

As is the case with most tools, the quality of the product is dependent on the skill of the user. The person who actually applies the system should have skills in plant ecology and be knowledgeable of the area. While the system helps the manager decide which species need what management efforts, it does not tell the manager what that management effort should be.

Most site managers are looking for a decision tool that is quick and cheap to apply and will provide all the answers. Unfortunately, APRS is neither. While more efficient survey methods and species fact sheets are being developed, managers still need to conduct thorough site surveys and often intensive literature searches. However, the outputs of the APRS do help managers design and build an invasive plant management plan. Furthermore, the system is purposely designed to allow flexibility in applying the information to a specific site with its own unique ecological and political setting.

For more Information:

Ron Hiebert

Colorado Plateau Ecosystem Studies Unit,

Northern Arizona University, P.O. Box 5765

Flagstaff, AZ 86011-5765

ron.hiebert@nau.edu

APRS is based on the system presented by R. Hiebert and J. Stubbendieck in the Handbook for Ranking Exotic Plants for Management and Control. Automation and revision of the system was a team effort involving Diane Larson and Jim Bennett of the USGS Biological Resources Division; Karl Beres from Ripon College; Diane Beres, David Lime, Anthony Starfield, and Jerrilyn Thompson from the Univeristy of Minnesota; and Ron Hiebert of the National Park Service.

Visit the APRS Web Site:
http://www.npwrc.usgs.gov/resource/literatr/aprs/

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