A level Biology exam revision resources written by A level Examiners


Once a quadrat has been placed either randomly or systematically the organisms within it must be surveyed. This can be done simply by counting the number of individuals of each species in the quadrat. This method is a good way of establishing the population density of the species. However this method may be overly time consuming if there are very large numbers present.

Another method of measuring the organisms within a quadrat is to measure the percentage of the quadrat that is covered by the organisms of particular species. This provides an estimate of the abundance of the species present based on the proportion of the sample area that they cover, not the number of individuals in the species. The diagrams below show how this can be done objectively.

Frame Quadrats are simply subdivided quadrats which can be used to estimate percentage cover of plants.


In this quadrant estimating the percentage cover is done by eye and is therefore subjective.


With the frame quadrant, the method presented below, can be followed to estimate percentage cover.

Using a method to estimate percentage cover using a frame quadrat.


Count whole squares occupied by plant.


Count the part occupied squares and estimate how many whole squares this equates to.


Add these figures together, divide by the total number of squares in the quadrat and multiply by 100 to give the percentage cover.

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