Sampling with quadrats and transects

Overview

Using random quadrats to find the mean number of a plant per square metre, generating random coordinates, percentage cover, belt transects across a changing habitat, measuring light and soil moisture, sample size and sources of error, and the mean, median and mode of quadrat counts.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a quadrat?

   Model answer

   A quadrat is a square frame of known area placed on the ground so the organisms inside it can be counted.

2. 2

   Describe how quadrats are used to find the mean number of daisies per square metre in a field.

   Model answer

   Place several quadrats at random positions, count the daisies inside each one, then divide the total count by the total area sampled.

3. 3

   Explain why quadrat positions must be chosen at random when sampling an area of even habitat.

   Model answer

   Random placing removes the bias of choosing where to sample, so the results are more likely to represent the whole area.

4. 4

   Describe how random positions for quadrats can be generated in a field.

   Model answer

   Lay two tape measures at right angles to make a grid, then use pairs of random numbers as the coordinates for each quadrat.

5. 5

   What is percentage cover, and when is it recorded instead of counting individual plants?

   Model answer

   Percentage cover is the proportion of the quadrat area filled by a species, used when plants such as grass or moss cannot be counted as separate individuals.

6. 6

   What is a belt transect?

   Model answer

   A belt transect is a line laid across a habitat along which quadrats are placed to record how the species present change with distance.

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