Species-rich forests store twice as much carbon as monocultures
On average, species-rich subtropical forests can absorb twice as much carbon as monocultures. This is the result of an international study carried out as part of a unique field experiment led by Martin Luther University Halle-Wittenberg (MLU), the German Centre for Integrative Biodiversity Research (iDiv) and the Chinese Academy of Sciences.
The experiment consists of specially created forests in China; for the study, data from experimental areas with a total of more than 150,000 trees were evaluated. From the researchers’ point of view, the results suggest that many different tree species can be used for reforestation. This could be used to protect both species and the climate.
In 2009, tree mixes with different numbers of species were planted – from monocultures to species-rich forests with 16 different tree species. After eight years, such a forest stored an average of 32 tonnes of carbon per hectare in its above-ground biomass. An average monoculture, on the other hand, stored only 12 tons of carbon per hectare, not even half of it. If a forest stores more carbon, this helps to reduce greenhouse gases and at the same time indicates a high productivity of the forest.
Reforestation with different tree species helps biodiversity and climate
The fact that productivity increases with species diversity has already been shown by experiments in meadow ecosystems in Europe and the USA, for example in the “Jena Experiment”. For the forest, on the other hand, a small effect of species diversity was suspected, since it was assumed that all tree species had similar ecological niches. Obviously, however, this assumption was wrong, because in the forest experiment biomass increased just as quickly as in grassland. As a result, even after four years there were clear differences between the monoculture and the species-rich forest.
These results have great ecological and economic significance, emphasises Prof. Bernhard Schmid from the University of Zurich, the last author in the team of over 60 authors of the study. A previous study had already shown a positive relationship between biodiversity and carbon storage. However, the previous study was based on pure observations and therefore it was not possible to clearly prove that the higher biodiversity was the reason for the higher productivity.
With a mixture of native tree species, it is therefore possible to achieve higher productivity and thus better protect the climate. Species-rich forests are also less susceptible to diseases or extreme weather events, which are becoming increasingly frequent as a result of climate change. And they contribute to the conservation of biodiversity, which is threatened worldwide.
Mixed tree cultures are also an economic gain
The study also shows that it pays off economically to use mixed cultures for afforestation, according to the authors of the study: “If the effects observed in the experiment on the world’s forests are extrapolated, a decline in tree species by ten percent would lead to production losses of 20 billion US dollars per year worldwide.