Species diversity is measured through a combination of species richness (the number of species present) and species evenness (the abundance of each species). Species richness and evenness can be combined into a single indicator, and in ecology the Shannon Index is commonly used.
To calculate species diversity we need to know the area of the forest and the area occupied by each species. This information can come from a forest survey or from inventory data.
Species diversity can be calculated at many scales, whether for a forest management unit, the whole forest area, regionally, or even nationally.
Generally the larger the forest area the more species are present, we need to consider this when comparing forests.
Why should we measure it?
Increasing forest tree species diversity is an important component in building our resilience to climate change and to reducing the risk from pests or pathogens damage.
Measuring species diversity allows us to:
identify forests with lower/higher species diversity
compare the diversity of different potential management approaches