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Presence/Absence

Method Type

Qualitative

Other Names

Description and Uses

Presence/absence sampling is nothing more sophisticated than determining whether a species (or other object or event) occurs at a location or not. In general, presence/absence is applied in a qualitative manner because parameters defining the specific area to be searched and the amount of effort to devote to searching are not specified.

Advantages and Limitations

According to Elzinga et al., the primary advantages of presence/absence sampling for monitoring are, “… that no special skills are required (anyone who can recognize the species can do the monitoring) and that the monitoring requires very little time.” Presence/absence sampling can be a very fast method for collecting information if the only thing that is needed is knowledge of whether or not something was present. As such this method can perform well for measuring or understanding the distribution of things across landscapes. A significant limitation of this method, however, is that it does not provide information on things like the abundance, density, or condition of individuals at the site. These factors can be important leading indicators of changes that might take a long time to be expressed through changes in distribution.

Many of the quantitative methods for assessing cover and density (e.g., Line-Point Intercept) tend to under-represent species that are not common in the plot. For many applications this is not an issue, but often times sampling needs to cover multiple objectives. For example, when monitoring rangeland condition, bare ground cover and presence of invasive species might be important. Transect-based cover measures might miss invasive species that occur in the plot. For this reason, it is common to do some presence/absence sampling within a plot to augment other data collection efforts.

Manuals/Instructions

  • 2009 National Resources Inventory (NRI) Grazing Land On-Site Study Handbook of Instructions (March 26, 2009). Chapter 16 - Plant Census. This reference specifies a more quantitative approach to presence/absence sampling through fixed plots and times searches.
  • see the Plant Species Richness page for information on a related presence/absence-based method.

Similar Approaches

The Plant Species Richness method - based on the Modified Whitaker Approach - is essentially a quantitative version of presence/absence sampling where plots of fixed size are defined and searched for a specified duration.

Rangeland Application References

  • The 2009 NRI Grazing Land Study used presence/absence searches to census for rare and invasive plants in their study plots
  • Many habitat or distribution modeling projects use presence/absence data.

Web Search Results

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References

  • Elzinga, C. L., D. W. Salzer, and J. W. Willoughby. 1998. Measuring and monitoring plant populations. BLM Technical Reference 1730-1. BLM National Applied Resource Sciences Center. Denver, Colorado.

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field_methods/presence_absence.txt · Last modified: 2012/03/08 15:35 by jgillan