Because habitats are made up of many species, it is usually too difficult to measure all the biodiversity. So biologists chose to measure a smaller part of the biodiversity of an area. For example, they may study the biodiversity of trees or birds in a tropical rainforest, the insects or flowering plants in an English meadow, or the fish living on a coral reef. When biologists measure biodiversity in an area they usually count two things: 1. the number of species, and 2. the number of individuals (or abundance) of each species Biologists often want to compare different areas to see which has the highest level of biodiversity. Or they may want to monitor one site over a long period of time to see if the biodiversity at that site is changing. To make direct and accurate comparisons, biodiversity must be measured in the same way every time. This means that a standardised sampling method must be used to record the biodiversity at each site. For example, a common method used to study the biodiversity of trees in a rainforest is to mark out a one hectare plot (100 m x 100 m) and then identify and count all the trees with a trunk larger than 10 cm diameter. These studies have shown that the rainforest of Borneo (a large island in Southeast Asia), has the highest number of tree species per hectare of any forest in the world. The sampling method used to record biodiversity must be appropriate to the group of animals or plants being studied. For trees, a large plot size is used but for insects a smaller sampling area can be used. Do you know why? On the savannahs of East and Southern Africa, some types of big animals that move over large distances, such as elephants and rhinos, are best recorded from an aeroplane. Another common method to sample biodiversity is quadrat sampling. The Fieldwork section explains two methods you can use to sample plants and invertebrates with a quadrat. Go back