In a new study published in the journal Nature, researchers have analyzed data from hundreds of plots in Canada’s National Forest Inventory (NFI). The goal was to clarify the relationship between tree diversity and changes in carbon and nitrogen storage in soils from natural forests. The experts found that preserving the diversity of forests potentially increases the accumulation of these two substances in the soil, helping to sustain soil fertility and mitigate climate change.
Forest soils play a major role in sequestering carbon extracted from atmospheric CO2 during photosynthesis, storing at least three times more carbon as living plants do. At the same time, nitrogen is an essential nutrient driving carbon assimilation and plant growth in forests.
Although a variety of biodiversity-manipulation experiments have already suggested that higher tree diversity can lead to a larger accumulation of carbon and nitrogen in forest soils, this is the first study to provide evidence of a similar outcome in natural forests.
The researchers analyzed organic soil horizon samples from 361 plots and mineral soil horizon samples from 245 plots covering much of Canada’s landmass, and hosting a variety of fir, maple, pine, spruce, hemlock, cedar, and other tree species.
Then, by comparing data from two NFI sample-plot censuses – one from 2000-2006 and another from 2008-2017 – the experts calculated changes in soil carbon and nitrogen storage over time and assessed the relation between these changes and tree diversity, which was quantified as a combination of tree richness (the number of tree species in a sample plot), species evenness (a measure of the relative abundance of tree species), and functional diversity (the various functional traits of tree species within a community).
The analysis revealed that increasing species evenness from its minimum to its maximum value enhanced carbon storage in the organic soil layer by 30 percent and nitrogen storage by 42 percent, while increasing the functional diversity of trees to its maximum value enhanced carbon storage in the soil mineral layer by 32 percent and nitrogen storage by 50 percent.
“Our study, for the first time, shows the sustained benefits of tree diversity in storing soil carbon and nitrogen in natural forests,” said study lead author Xinli Chen, a postdoctoral fellow in Forest Ecology at the University of Alberta in Canada.
“A greater diversity of species translates into a mixture of different types of trees with different ways of acquiring and storing biomass—both in live trunks, roots, branches and leaves and in newly dead and decaying plant detritus on and in the soil,” added co-author Peter Reich, the director of the Institute for Global Change Biology (IGCB) at the University of Michigan.
These findings suggest that promoting tree diversity not only increases productivity but can also help mitigating climate change and reducing soil degradation, thus highlighting the importance of biodiversity conservation in forests and guiding efforts to use forests for carbon and nitrogen sequestration.