Presence / absence survey methods

Presence / absence survey methods

It is common to standardise presence/absence surveys by either the time spent searching and/or the area searched. In most cases, with a survey for a known species population, the search area can be narrowed down using information about the species, its ecology and physical habitat requirements (such as calcareous soils or ultramafic rock) obtained from local floras, herbaria, interviews with local botanists and past survey information. This will help narrow down where the species will most likely occur and will help determine the search area or site that is the target for your survey.

Once the target area is decided then relocating plant populations can involve a standard parallel-line search. This is where larger study areas are divided into blocks no larger than 10 hectares. Surveyors start at one end of one block and systematically move across the shortest distance in a series of parallel lines documenting all the populations that are found. The closer the transects are to each other across the blocks the more accurate the survey but the more time it takes.

When found, then details of the plant population should be recorded as well as the date and name of observer. This can be done by collecting a herbarium specimen or by recording details of the site on a record sheet or using a GPS unit. In most cases a species record form or map is used on which the locations of the species are recorded. Many varieties of field record sheets are used but they must include the following fields: observer, date, and time spent searching. If a GPS unit is used then an accurate location should be recorded.

This page last updated on 23 Sep 2012