Using sampling techniques

Sampling plants

It is impossible to count all the plants in a habitat, so a sample is taken. A technique that is often used to sample plants is a quadrat. It marks off an exact area so that the plants in that area can be identified and counted. The number of plants counted in a sample of areas can be multiplied up to give an estimate of how many of that plant type are in the whole habitat.

A student crouches over a quadrat taking measurements.

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.

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.

Setting up pitfall traps:

  • 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.
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