You first need to calculate the total area of your forest and the area covered by each species. This may be available from inventory data or you might need to carry out a forest survey.
If you have a list of smaller forest components you need to calculate the total area for each species. You can do this in Microsoft Excel or any statistical or GIS software. A worked step by step method using Excel is available.
Species richness is the number of species present in the forest. For small datasets it can be calculated by counting the number of species in your forest manually. For larger datasets we provide a worked example.
Species evenness describes the relative abundance of each species. Once you have measured the area of each species in your forest you can see how evenly they are distributed. The percentage area of the most dominant species can be helpful in understanding evenness. A worked example is available.
The Shannon Index
The Shannon Index combines species richness and evenness into a single indicator. You can calculate the Shannon Index in Microsoft Excel or other statistical software.
We provided an example and step by step example using Excel which you can download below.