Pros and cons of presence / absence surveys

Pros and cons of a presence /absence survey

Presence/absence surveys tend to record presence only. Absences cannot be absolutely confirmed and often require several subsequent surveys to confirm. This technique can therefore produce false negatives. That is, an absence does not necessarily mean the plant is not there, only that it has not been detected during the survey.

In addition, this method provides no information on the trend in the population unless the species disappears entirely. Because it is a crude and basic measurement you are unable to monitor mortality and recruitment. There are also reasons why relocating plant populations can be problematic. Firstly, errors may have been made when the site was recorded during an earlier survey. Original observations may have been made many years ago and changes at the site may have occurred since then including changes to the name of the location and changes to the vegetation. Landmarks used in directions to the site, such as fence lines or tall trees, may not be there any more. The information obtained cannot be applied in very many ways for effecting improved management of a species in the wild.

On the other hand, this method requires few specialist skills except an ability to identify the species. Monitoring in this way also takes very little time (compared with other techniques) and can often be done by field staff when doing other work. Presence/absence surveys of a species population or a number of populations are adequate to determine, in a crude way, the annual status of a target plant population.

This page last updated on 23 Sep 2012