31 July 2018

Publication in Nature Ecology and Evolution

New theory unravels social network of trees

How is it possible that so many different tree species live side-by-side in forests? An intriguing question for scientists for decades, researchers have now discovered a way to mathematically describe the social network that creates and maintains biodiversity in forests. The research, led by researchers from Utrecht University and the University of Kansas, has been published in Nature Ecology and Evolution. In our age of global biodiversity loss, the findings can benefit nature conservation and restoration efforts.

This breakthrough enables the researchers to calculate whether soil microbes are strong enough to create and maintain biodiversity. “We found a way to characterize the interactions of any tree-microbe network, whether it consists of 2 or 2000 species, by a single number. This tells us whether soil microbes enable these tree species to live together or not,” explains Dr Maarten Eppinga, an Assistant Professor at Utrecht University and lead author of the research.

Unlike Facebook

Soil microbes influence and connect tree species. Through these so-called plant-soil feedbacks all tree species in a forest are connected, forming a social network of ecological interactions. “Unlike Facebook, plant-soil feedbacks create networks in which every member is connected to all the other members. This creates an enormous number of different pathways through which tree species can influence each other. Even in a community of only ten tree species, there are already millions of such pathways. It is therefore quite remarkable that we were able to derive mathematical results that hold for communities of any size,” adds Dr Mara Baudena, an Assistant Professor at Utrecht University and second author of the study.

Warm and cold forests

The authors tested their theory using observations of tree species diversity on more than 200,000 locations in North America. “We had previously found spatial patterns of seedlings consistent with strong plant-soil feedback in the data. Our new theory enables us to demonstrate that these feedbacks can explain the high diversity of tree species in warm, moist forests in the South East of the United States and the decline in tree diversity in colder and drier forests,” says Jim Bever, professor at the University of Kansas and senior author of the study.

Maarten Eppinga

Maintaining forest diversity

Nature conservation and restoration efforts benefit from a better understanding of what created this diversity in the first place. “Our new theory can help us in identifying species that are playing a key role in maintaining forest diversity. It will also enable more detailed projections of how diversity might change when forests are disturbed by human activities or climate change,” Eppinga concludes.


Frequency-dependent feedback constrains plant community coexistence
Maarten B. Eppinga *, Mara Baudena *, Daniel J. Johnson , Jiang Jiang, Keenan M. L. Mack, Allan E. Strand and James D. Bever
Nature Ecology and Evolution, 2018

(* = from Utrecht University)