In ecology, one aspect of an ecosystem which is studied by scientists is population. Because it can be difficult to accurately measure plant or animal populations, several methods have been devised to do estimate populations. One of these methods is random sampling with quadrats.
Quadrat sampling is done only to immobile organisms, namely, plants. Also, this type of sampling is done to find the population of one organism at a time.
The area which a population estimate is desired is divided up into many sections, or, quadrats. The quadrat shape is usually square or rectangle, but it can be a multitude of shapes. After dividing a region into quadrats, several quadrats are randomly chosen.
In these quadrats, scientists physically count each organism of the total population. This provides a proportion; scientists then calculate the amount of organisms per quadrat and multiply it by the number of quadrats to provide an estimate of the total population.
Citations:
Ecosystems & Human Influence. http://www.biologymad.com/master.html?http://www.biologymad.com/Ecology/ecology.htm. Biology Mad. April 5, 2004.