Hidden ‘highways’ connect Brazil’s rainforests
University of Exeter
image:
An Inga tree (I. affinis) growing alongside a river in the cerrado savanna region of central Brazil
view moreCredit: RT Pennington
Forests flanking Brazil’s rivers act as “highways” that have allowed tree species to move between the Amazon and Atlantic rainforests for millions of years, new research shows.
The two rainforests are separated by hundreds of miles of dry forest and savanna, where most rainforest trees cannot survive.
Until now, it was thought that tree species only passed between the Amazon and the Atlantic forests during periods long ago when the climate was wetter and much of South America was covered in rainforest.
But the new study – led by the Royal Botanic Garden Edinburgh (RBGE) and the University of Exeter – reveals a different story.
“Rather than tree species being exchanged during specific wetter periods in the past, we found that species have dispersed consistently over time,” said Dr James Nicholls, of RBGE.
“This probably happens slowly, by generations of trees growing along the ‘highways’ provided by rivers that run through Brazil’s dry ecosystems.”
The research team – including scientists from Brazil – studied 164 species of Inga trees, which are common in Latin American rainforests.
By analysing DNA, they reconstructed the trees’ family tree – seeing when each species split from its various ancestors. They then mapped where each species is found, allowing them to examine patterns of movement between the Amazon and Atlantic rainforests.
They found 16-20 “dispersal events” when species arrived in the Atlantic forest from the Amazon, and successfully established themselves. These occurred throughout the evolutionary history of Inga – not just during periods when humid forest covered much of Brazil.
Meanwhile, the study only found one or two occasions when species moved from the Atlantic to the Amazon forest. The researchers think this may reflect the relative size of the forests – with the vast Amazon simply producing more outflow of tree seeds.
The findings highlight the importance of conserving riverside forests – which are protected in Brazilian law.
Professor Toby Pennington, from Exeter’s Department of Geography and the Global Systems Institute, and RGBE, said: “This legal protection – and efforts to preserve these riverside forests – are highly valuable for long-term habitat connectivity.
“The study also tells us something fundamental about the history of the incredible biodiversity of the Atlantic rainforest, which contains about 3,000 more plant species than the Brazilian Amazon.
“Only 20% of the Atlantic rainforest now remains intact.
“In the short term, we need to protect these precious rainforests. In the long term, our study shows that we must also conserve the connections between them.”
The study was funded by the United States National Science Foundation.
The paper, published in the journal Proceedings of the Royal Society B, is entitled: “Continuous colonization of the Atlantic coastal rain forests of South America from Amazônia.”
an Inga tree (I. sessilis) from the Mata Atlantica
Credit
RT Pennington
Journal
Proceedings of the Royal Society B Biological Sciences
Article Title
Continuous colonization of the Atlantic coastal rain forests of South America from Amazônia
Amazonian mangrove forests provide nutrients for the ocean
New study highlights the role of mangrove systems in
global biogeochemical cycles
Mangrove forests are not only critical carbon sinks and biodiversity hotspots but also play a key role as suppliers of trace elements to the ocean. This is shown by a study conducted by the GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany. For example, mangrove systems along the Amazon coastline release about 8.4 million grams of dissolved neodymium into the ocean each year – 64 percent of the total neodymium input in this region. Similar processes are likely for other essential trace elements, such as iron or manganese, which are crucial for marine ecosystems and the carbon cycle.
“Our research shows that mangroves play a central role in the global cycle of trace elements,” explains Dr Antao Xu, first author of the study from GEOMAR. “They act as biochemical reactors, releasing nutrients and metals into coastal waters through processes such as sediment dissolution and pore water exchange.”
Mangrove Systems as "Nutrient Pumps"
The research team analysed water samples from coastal waters, estuaries and mangrove sediments along the Amazonian coast. Distinct isotopic patterns of neodymium and hafnium were identified, revealing their origin and the interactions between sediments, pore water, and seawater. “Mangroves are not only buffer zones that retain material from land; they are also key players that process and selectively release these substances and micronutrients into the ocean,” says Professor Martin Frank, co-author of the study and head of the research division Ocean Circulation and Climate Dynamics at GEOMAR. This exchange of substances supports coastal food chains.
Globally, mangrove systems contribute between six and nine percent of the total neodymium input to the ocean, according to the researchers. This contribution is comparable to the global input of neodymium from the atmosphere via dust.
Global Importance of Mangrove Conservation
The study’s findings underscore the urgent need to protect these threatened ecosystems. Xu states: “Mangroves sit at the interface between land and sea and provide invaluable services for biodiversity and climate regulation. Their prominent role as a source of trace elements is another compelling reason to prioritise their conservation.”
Journal
Nature Communications
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
The Amazonian mangrove systems accumulate and release dissolved neodymium and hafnium to the oceans
Article Publication Date
8-Jan-2025
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