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Quick guide: plain English, key facts and method
In plain English: You cannot count every plant in a field, so you count a few samples and scale up to estimate the whole population.
Key facts
- A quadrat is a square frame used to sample organisms.
- Place quadrats at random (for example using random coordinates on a grid) so the sample is not biased.
- Mean number per quadrat = total counted ÷ number of quadrats.
- Estimated population = mean number per m² × total area in m².
- A 50 cm × 50 cm quadrat has an area of 0.25 m², so multiply by 4 to get the number per m².
- Use a transect (a line with quadrats at regular intervals) to see how a population changes with distance.
How to do it
- Find the mean number per quadrat.
- Convert to the mean number per m² if the quadrat is not 1 m².
- Work out the total area: length × width.
- Multiply the mean per m² by the area.