Many countries have climate-protection policies designed to conserve tropical forests to keep their carbon locked up in trees. But a focus on policies to conserve tropical forests for their carbon storage value may imperil some of the world's most biologically rich tropical forests. This is the conclusion of new research by, amongst others, Frans Bongers and Marielos Pena Claros.
The new study, led by the University of Leeds, suggests these policies could miss some of the most diverse forests because there is no clear connection between the number of tree species in a forest and how much carbon that forest stores. International programmes often encourage the conservation of forests with high carbon stocks, but until now it was not known whether these programmes would also automatically protect the most biodiverse forests. “And probably they don’t,” says Frans Bongers.
Scientists from 22 countries measured both tree diversity and the amount of carbon stored in 360 locations across the lowland rainforests of the Amazon, Africa and Asia. The results, published in Scientific Reports, show that African tropical forests, spanning the Congo and West Africa, store high levels of carbon but are the least species rich. Forests in the Amazon and Asia, mostly in Borneo, have the greatest diversity of tree species, yet the Amazon tends to store less carbon per hectare than forests in Africa and Asia.
Although sites with more species usually tend to lock up more carbon, this doesn't always work for tropical forests. Frans Bongers: “Beyond a certain point of species richness, more species make no difference to carbon stocks. We found forests with relatively few species that stored a lot of carbon, while some forests with a high biodiversity stored remarkably little carbon. However, the huge value of tropical forests goes beyond carbon stock alone. Preserving biodiversity is equally important. Borneo, for example, is under extreme pressure from deforestation, but it's also a place where extremely high tree diversity and carbon stocks often coincide. Protecting these forests helps both biodiversity and climate protection goals.”