Quadrat Sampling

Quadrats provide quantitative data either as numbers of individuals or as percentages. They are generally square, wire frames that are 50 cm by 50 cm and they can be used to estimate or count plants and slow moving animals. Their main limitation is that, due to their size, quadrats can only really be used to study the ecology of habitats where trees and bushes are widely spread or completely absent.

Quadrat sampling consists of randomly placing a quadrat on the ground in the area to be sampled. The position of the quadrat must not be chosen by the experimenter. Numbers and types of plants and animals can then be estimated for the whole habitat by counting them in the individual quadrats. The method is very useful as it is quick and easy to do but needs to be used with care to give valid results. When using quadrat sampling, either actual numbers can be counted or the percentage area covered by each species of plant is estimated. The results can then be scaled up to the area of the area being studied. If the total area of habitat is 200 square meters and the total area sampled using quadrats was 10 square meters, the quadrat count just needs multiplying by 20 to give a result for the full habitat.

Where the environment is not uniform, analysis along a line transect can also be carried out to establish gradual changes (across a field that is boggy at one side but dry at the other for example). A relationship between the number of organisms and the environmental conditions can be worked out using this method.

Try this quiz to see how much you know about using quadrat sampling when studying the ecology of habitats.