Ann Arbor Times

A new study led by the University of Michigan has found that biodiversity plays a more significant role in promoting tree growth in wetter climates than in drier ones. The research, published in Nature Ecology & Evolution, analyzed data from 15 tree diversity experiments worldwide, covering 100,000 trees and nearly 130 species.

“Diversity matters everywhere we look,” said Peter Reich, professor of environment and sustainability and director of the Institute for Global Change Biology at the University of Michigan. “But in our experiments, we see it matters more in the wetter climates.”

The project drew on the Tree Diversity Network, which includes 34 sites globally and is recognized as the largest network of its kind. The study involved collaboration among researchers from almost a dozen countries and over 30 institutions. Funding came from international organizations such as the U.S. National Science Foundation, German Research Foundation, São Paulo Research Foundation, and University of Chinese Academy of Sciences.

“This provides a more nuanced insight into how biodiversity works in different environments,” said Reich, who is also a professor at the University of Minnesota. “If you’re thinking of restoring or regrowing, it makes a lot of sense to plant diverse trees,

especially in wetter areas.”

Reich clarified that “wetter” forests are not limited to tropical rainforests; by their criteria, regions like Michigan’s forests also qualify as wet.

Lead author Liting Zheng explained some of the findings: “We find a tree growth boost in diverse tree neighbourhoods with different species and functional traits—for example, specific leaf area and wood density.” Zheng conducted this work as a postdoctoral fellow at Michigan’s School of Environment and Sustainability and now works at the German Center for Integrative Biodiversity Research.

“Our results highlight the importance of establishing and maintaining high neighborhood diversity in forest management—especially to maximize the potential of biodiversity as a nature-based climate solution in wetter regions.”

Previous studies have produced mixed results regarding biodiversity’s benefits under varying climate conditions. Reich noted that many earlier projects focused on single sites or used broad measures of biodiversity across entire communities rather than examining individual trees and their immediate neighbors.

“What’s unique about our study is it has 15 long-term experiments with lots and lots and lots of trees,” Reich said. “Then, rather than looking at an entire community, we looked at every individual and eight or so of its neighbors and asked, ‘Are those neighbors diverse or not?'”

He acknowledged one limitation: all studied trees were relatively young (4 to 14 years old), but suggested there is no clear reason why results would differ for older forests.

The study also found that while biodiversity has a greater effect on growth in wetter climates overall, this impact does not increase during particularly wet years within those climates.

“Diversity appears to be better suited for the average condition, which matters for management,” Reich said. “There’s thinking that biodiversity is really going to help you when you have those extreme years and some evidence supporting this idea, but in our data this was not the case.”

Kai Zhu and Inés Ibáñez from Michigan’s School of Environment and Sustainability also contributed to the research.