For millions of years, Brazil’s Amazon and Atlantic rainforests have been home to some of the world’s most diverse ecosystems. But how have tree species managed to migrate between these two vast and isolated forests, separated by dry savannas and unsuitable landscapes?
New research has uncovered a fascinating answer: riverside forests serve as hidden “highways” for tree migration, facilitating the movement of species across otherwise impassable terrains. This discovery sheds light on the long-term connectivity of South America’s rainforests and underscores the importance of conserving riparian ecosystems.
The Discovery: A Continuous Exchange of Species
A study led by scientists from the Royal Botanic Garden Edinburgh (RBGE) and the University of Exeter has challenged previous assumptions about tree migration. Traditionally, scientists believed that rainforest trees could only migrate between the Amazon and Atlantic forests during ancient wet climate periods when these ecosystems were more connected.
However, DNA analysis of 164 species of Inga trees—a diverse genus of tropical trees common in Latin America—reveals a different story.
🔍 Key Findings:
✅ Migration has been occurring continuously over time, not just during past wetter climates.
✅ Trees move gradually, generation by generation, along river corridors.
✅ There have been 16-20 documented dispersal events from the Amazon to the Atlantic Forest.
✅ Movement in the opposite direction (Atlantic to Amazon) was extremely rare.
This suggests that Brazil’s rivers act as natural bridges, allowing species to spread and adapt over millions of years, despite the presence of dry forests and savannas that would otherwise be barriers to migration.
Examples of Tree Migration in Other Parts of the World
This phenomenon of tree migration through natural corridors is not unique to Brazil. Similar patterns have been observed in various parts of the world:
🌿 1. The African Rainforest Migration (Congo Basin to West Africa)
- The Congo Basin and West African rainforests are separated by dry savanna regions.
- Studies on mahogany and iroko trees show that species have migrated over thousands of years via river corridors.
- The Niger River has played a major role in the dispersal of plant species between Central and West Africa.
🌲 2. Boreal Tree Migration in North America
- As glaciers retreated after the Ice Age, tree species like spruce and pine migrated northward.
- River valleys and lowland wetlands helped trees expand their range faster than those relying solely on wind or animal dispersal.
🍃 3. The Role of the Mekong River in Southeast Asia
- The Mekong River has allowed tree species to migrate between Thailand, Cambodia, and Vietnam despite dry monsoon forests acting as barriers.
- Species like Dipterocarps (which dominate Southeast Asian rainforests) have used riverbanks as migration corridors.
These examples confirm that rivers act as natural biodiversity highways, facilitating migration across different ecosystems worldwide.
Tracing Tree Migration Through DNA Analysis
To uncover these migration patterns, researchers examined the genetic history of Inga trees. By reconstructing their family tree and mapping their geographical locations, scientists could determine when and how species moved between rainforests.
One striking observation is the dominance of Amazon-to-Atlantic migration. Researchers believe this is due to the sheer size of the Amazon, which produces a higher volume of tree seeds that eventually find their way into the Atlantic Forest through river pathways.
🌿 Why is this Important?
✔️ It reveals that rainforest ecosystems are more interconnected than previously thought.
✔️ It highlights the critical role of rivers in biodiversity conservation.
✔️ It challenges the idea that species migration is solely climate-dependent.
The Importance of Conserving Riverside Forests
The study reinforces the urgent need to protect riparian (riverside) forests, which are already recognized under Brazilian environmental laws. These ecosystems serve as crucial migration corridors, ensuring the long-term survival of many rainforest species.
🚨 Conservation Challenges:
🔹 Only 20% of the Atlantic Forest remains intact due to deforestation.
🔹 Climate change and human activities threaten key river ecosystems.
🔹 Disrupting migration corridors could impact the genetic diversity and survival of species.
Professor Toby Pennington from the University of Exeter emphasizes the importance of not just protecting existing forests, but also maintaining the connections between them. Preserving these natural highways is essential for the continued exchange of species, ensuring the resilience of South America’s rainforests for generations to come.
Looking Ahead: The Future of Tree Migration Studies
This study opens new doors for understanding how tree species adapt to environmental changes and migration barriers. Future research could explore:
🌍 How climate change might alter these migration pathways
🌱 Whether other tree species follow similar dispersal patterns
🌊 The role of river systems in maintaining biodiversity under global warming
By recognizing rivers as vital biodiversity corridors, conservation efforts can be better targeted to protect both trees and the ecosystems they sustain.
The discovery of tree migration “highways” connecting Brazil’s rainforests challenges long-standing scientific assumptions and highlights the hidden power of rivers in shaping ecosystems. As deforestation and climate change threaten these natural corridors, protecting riverside forests is more critical than ever.
By preserving these migration pathways, we can help sustain the incredible biodiversity of South America’s rainforests, ensuring they continue to thrive for future generations.
🌿 What are your thoughts on tree migration and rainforest conservation? Let us know in the comments! 🌍💬
📖 Reference:
Nicholls, J. A., Ringelberg, J. J., Dexter, K. G., et al. (2025). Continuous colonization of the Atlantic coastal rain forests of South America from Amazônia. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2024.1559
