The evenness of species within a community is key to increasing forest productivity 

3 May 2023

New research shows that high forest productivity is not only the result of how many different species occur in a forest, but also how abundant the species are.

Typically, a greater number of species increases an ecosystem’s productivity. However, a new study shows that the effects of diversity are not only a matter of species richness. If many species coexist in a forest, even distribution of species abundances is key for high ecosystem diversity and productivity.  

Biodiversity is an essential factor for ecosystem health and productivity. A higher biodiversity generally leads to higher productivity. Indeed, the number of species in an ecosystem has been found to positively correlate with forest productivity. Previous research, however, has also pointed to a limit in increasing forest productivity at a high number of coexisting species. What is the reason? 

Sergio de Miguel, a researcher at Forest Science and Technology Centre of Catalonia (CTFC) and professor of forest science at the University of Lleida, has participated in a new publication in Journal of Ecology that provides evidence at global scale that the number of species, also known as species richness, is not sufficient to measure the effect of biodiversity on forest productivity. Biodiversity is a product of species richness, but also the relative abundance of species in the community (evenness). Evenness refers to the distribution of species abundance: for example, a plot with 50 trees and five species at each ten trees can be considered even. However, a forest plot with 46 trees of one species but one each of the other species would be considered uneven.  

Based on data from over one million forest plots worldwide, the study shows that there is a negative relationship between the richness and the evenness of species within forests around the world. Forests with a high species count therefore tend to be highly uneven, with a few species dominating the community, while the majority of species are rare. In these cases, evenness will be more important for improving forest productivity than increasing the number of species.  

“Our work shows how the number of trees within a species is as important as the number of species a forest is home to. If we want to increase the productivity of forests, we need to take evenness into account,” stresses de Miguel.  

Overall, this study demonstrates the importance of species evenness in influencing forest diversity and productivity. At a time when diverse and productive forests are needed to fight climate change and biodiversity loss, understanding the role of species abundances is critical for guiding ecosystem conservation and management.  

Further information:  

Last modified: 3 May 2023