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Forests are vital for climate regulation and biodiversity, yet they face unprecedented threats from human activities and climate change. Understanding what drives tree species diversity is essential for conservation. While factors like temperature, rainfall, and soil fertility have been widely studied, the role of mutualistic interactions, particularly mycorrhizal symbioses, remains underexplored. A recent paper by Feng Jiang et al. (with input from WILDCARD’s partner Wageningen University & Research), published in Science Advances (2025) delves more deep into the topic.

Mycorrhizal fungi form partnerships with trees, exchanging nutrients for carbon and offering protection against pathogens. Two major types dominate: ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) fungi. EcM fungi tend to provide stronger protection and alleviate negative plant-soil feedbacks more effectively than AM fungi. This has led to the EcM dominance hypothesis, which predicts that forests dominated by EcM trees will have lower species richness. Conversely, the mycorrhizal mixture hypothesis suggests that diversity peaks when both EcM and AM trees coexist, due to complementary nutrient acquisition strategies. A third view, the integrated hypothesis, proposes that both mechanisms operate together, with diversity peaking in mixed communities but declining in EcM-dominated forests.

Until now, these hypotheses lacked global-scale testing. Jiang and colleagues addressed this gap by analyzing over 400,000 forest plots worldwide, examining how EcM tree proportion relates to species richness across latitude and aridity gradients.

Key Conclusions

The study revealed that the relationship between EcM tree proportion and species richness varies with environmental conditions:

• Low latitudes & moist conditions: A strong negative relationship supports the EcM dominance hypothesis. Here, EcM fungi reduce negative plant-soil feedbacks, favoring conspecific survival and lowering overall diversity.
• High latitudes & arid conditions: A unimodal relationship supports the mycorrhizal mixture hypothesis. Stressful environments weaken negative biotic interactions, making niche partitioning between EcM and AM trees more important for coexistence.
• Intermediate conditions: A negatively unimodal pattern aligns with the integrated hypothesis, suggesting both mechanisms operate simultaneously.

Overall, the study concludes that mycorrhizal symbioses are a critical, yet overlooked, driver of global forest diversity, interacting with climate and soil factors. This insight expands our understanding of biodiversity maintenance from an aboveground perspective to include belowground mutualisms.

What does rewilding mean to you? Together with our sister project REWRITE, Wildcard is inviting artists, photographers, creatives and storytellers to explore rewilding, not just as an ecological practice, but as a social and cultural response to today’s interconnected environmental challenges. Accepted mediums include photography, drawing, painting, sculpture, short video and audio, with submissions open to anyone aged 18 or older. 

The Initiative aims to bridge art, science, and society, translating complex ideas into accessible experiences that inspire societal transformation. By amplifying the missions of REWRITE and WILDCARD, the call unites coastal, marine, and terrestrial perspectives, offering hope and new ways forward. 

What do you gain by participating? 

If selected: 

• Be featured in an online zine available through WILDCARD and REWRITE websites and an international partner magazine. 

• Exhibit at physical events in 2026, including a “Rewilding Forum” in February 2026. 

• Share your work with a wide European audience, including actors from science, practice and policy. 

• Join a regenerative movement connecting art, science, and society. 

Learn more about the call via “Rewilding through Art” Open Call – Wildcard 

The passing of the EU Nature Restoration Regulation was a landmark decision for nature. This first-of-its-kind legislation aims to restore significant areas of degraded terrestrial and marine ecosystems across the EU member states. It implies an upscaling of ecological restoration far beyond current practice, which will require novel perspectives and solutions that are environmentally effective, economically feasible, and socially acceptable.

Join the European Climate, Infrastructure and Environment Executive Agency (CINEA), Horizon Europe projects wildE, REWRITE, WILDCARD, and the Society for Ecological Restoration Europe at this pioneering debate which will discuss the opportunities and challenges for implementing restoration in a way that “lets nature do the job”.

The event will bring together leading European experts from the research and policy sectors to consider where and when nature could help create ecosystems that support biodiversity, store carbon and enhance livelihoods which will enable both nature and people to better cope with the growing impacts of modern climate change.