Sampling techniques

It is impossible to count all the plants in a habitat, so a sample is taken. A quadrat is often used to sample plants. It marks off an exact area so that the plants in that area can be identified and counted.

A quadrat
A quadrat

Facts about quadrats

  • Quadrats should be placed randomly so that a representative sample is taken.
  • Many quadrats should be placed so that a representative sample is taken.
  • Quadrats may also be used for slow moving animals such as snails/slugs.

There are some limitations of using a quadrat. Human judgement can be an issue when using a quadrat. For example, some plants may be partially inside/outside a quadrat so there are basic rules that scientists follow that reduce the chance of human judgement affecting results.

Sampling animals

It is impossible to find and count all the animals in an area. You can get an idea of the variety and number by taking a sample.

Pitfall traps are often used to sample the small invertebrates living on the ground. You are likely to trap beetles and other insects, as well as spiders and slugs.

Cross-section of a bug trap showing an insect at the top of a hole. The hole is covered by a board which is raised from the ground at an angle by stones either side of the hole.

How to set up pitfall traps properly:

  • The top of the container should be level with the soil surface.
  • Cover the trap with a stone or piece of wood to keep out the rain, to make it dark and to stop birds eating your catch.
  • The traps must be checked often to avoid the animals escaping or being eaten before they are counted.
  • As with most methods a large number of traps makes results more reliable and minimises the effects of unusual results.