Tropical Rainforests Are Losing Their Resilience Worldwide

Tropical rainforests hold a wealth of biodiversity but are globally approaching a critical point. The drastic decline is happening faster than expected, concludes an international research team. The team includes biologist Hans ter Steege, affiliated with Utrecht University and the Naturalis Biodiversity Centre.

A team of researchers, including tree expert Hans ter Steege of Naturalis Biodiversity Center and Utrecht University, has provided new insights into the status of tropical forests worldwide. The team identified all tree species found in tropical rainforests, their distribution, and applied new calculations to these data. The results, published in the journals Nature and Science, collectively answer the question: how are tropical rainforests faring?

Understanding Forests Better

Tropical forests such as those in Africa, the Amazon, and Southeast Asia are hotspots of biodiversity. Researchers wonder why these areas were able to develop this way. What do these forests have in common, serving as a home to millions of species for centuries? Ter Steege and his team pondered these questions. They discovered that just a small number of common species contribute to half of the biodiversity in these forests.

“But despite differences in geography, climate conditions, and history, we find the same distribution of common species in these different forests,” says Ter Steege.

Common and Robust Species

The exact reasons for this are still a mystery. “Likely, the very common species are more resistant to insects and fungi than rare species, allowing them to reach higher densities,” says Ter Steege. Although researchers don’t fully understand how this distribution occurred, it helps them better understand and protect the biodiversity of forests.

Underestimated Decline

According to Ter Steege, this protection is urgently needed. Recent research, in which Ter Steege participated, showed that only 15% of the Atlantic Forest in Brazil remains. The rest has been cleared and damaged due to significant population pressure and deforestation in the country.

“As a result, more than 80% of the tree species unique to the Atlantic Forest in Brazil are threatened with extinction,” says biologist Renato Lima, who led the research.

When the researchers included population size in their calculations, they made the alarming discovery that many more species are threatened than previously thought. “It turns out that almost 5000 tree species found in the Atlantic Forest are threatened with extinction,” says Lima. “And thirteen species, found exclusively there, may have become extinct.”

Decline at Multiple Locations

Unfortunately, this decline is likely happening in multiple locations. “Our forecasts suggest that between 35 and 50% of tree species on earth could be threatened solely by deforestation,” Lima concludes. With the new models developed by the research team, the threat level of thousands of species can now be assessed on a large scale.

“This is essential,” says Ter Steege, “because the findings still underestimate the extent of future decline.” The research only considers past threats, such as deforestation, and does not account for future threats, such as climate change, which could further accelerate species extinction risks.

Stretching the Limits

This risk is confirmed in earlier research on the tropical rainforests of the Amazon, which did consider these future influences. For 65 million years, the resilient forests of the Amazon served as a buffer against climate change. That seems to be changing now. The research proves that the resilience of the once resilient forests of the Amazon is waning, putting them at a dangerous tipping point.

Rainforests Turning Into Savannas

“We estimate that by 2050, 10 to 47% of the forests in the Amazon will be exposed to such disturbances that the current ecosystem will collapse, leading to even more dramatic regional climate change,” says Ter Steege. According to the researcher, the rainforest will then turn into damaged patches of forest dominated mainly by a single species, such as bamboo. Another possibility is that it will turn into a plain savanna.

Restoring the Forest Balance

We can turn the tide, says Ter Steege. “To restore the resilience of tropical rainforests, global efforts must halt greenhouse gas emissions. Only then we can limit global warming.”

Local efforts can also help restore the forest balance. Ter Steege: “Firstly, deforestation and forest degradation must stop. Additionally, we need to promote forest restoration in affected areas.” This can be achieved, for example, by expanding protected and indigenous habitats.