Tropical trees die younger in hot temperatures

A new study from the University of Leeds has produced the first clear evidence that the lifespan of tropical trees will be limited by global warming. The researchers determined that the life expectancy of tropical trees is reduced once the temperature exceeds the critical threshold of 25 degrees Celsius.

As temperatures rise, the rate of tree mortality is expected to increase in tropical regions including the Amazon, Pantanal, and Atlantic forests. 

Even though tropical rainforests account for only 7 percent of the Earth’s total land area, these ecosystems provide habitats for about 50 percent of all plant and animal species. These rainforests also hold approximately half of all carbon stored in the world’s forests, which means that even small disruptions can cause significant CO2 emissions. 

“Many regions in the tropics are heating up rapidly and substantial areas will become warmer, on average, than approximately 25 C,” said study co-author Professor Manuel Gloor. “Our findings – which are the first to demonstrate that there is a temperature threshold – suggests that for trees in these regions, their longevity is likely to be negatively affected.”

“This indicates that tropical forests may be more vulnerable to increasing heat than has been previously thought,” noted Dr. Roel Brienen. “As a result of global warming, we therefore expect a shortening of tree lifespans in the tropics. These results are a warning sign that, along with deforestation, global warming adds extra stress on the Earth’s tropical forests.”

In collaboration with experts at the University of São Paulo, the researchers spent four years examining tree-ring data from more than 100,000 trees belonging to 400 different tree species from 3,000 sites across the globe.

“In the tropics, trees grow, on average, twice as fast as those in cooler regions of the world. But they also have a shorter average lifespan of 186 years, compared to 322 years of trees in other climates. Our analysis suggests that the life-spans in the tropics will likely decrease further still,” explained study lead author Dr. Giuliano Locosselli. 

“If tropical trees die earlier, this will affect how much carbon these forests can hold, raising concerns about the future potential of forests to offset CO2 emissions from fossil fuel burning. It could also cause changes in biodiversity and a decrease in the number of species on the planet.”

Currently, the average temperatures throughout tropical rainforests range from 21 to 30 degrees Celsius, but these numbers will continue to rise.

“Temperatures will keep rising in the near future even if we were to take drastic emissions reductions measures. Thus it is unavoidable that the critical threshold for tree longevity will increasingly be exceeded in the tropics and thus it is even more important to protect tropical forests and curb greenhouse emissions,” said study co-author Professor Marcos Buckeridge.

“While tropical rainforests in the Amazon are already close to this temperature threshold temperatures in the Congo are lower. But, with this great increase in temperature, we might begin to see signs of increased tree mortality. From this point of view, the scenario is quite bleak,” said Dr. Locosselli.

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer