A pair of recent studies show that rising temperatures are shortening the lives of trees in tropical forests and reducing their capacity to absorb carbon dioxide from the atmosphere.

This phenomenon is already being observed in parts of the Amazon, where the temperature has already crossed a critical threshold of 25°C (77°F); by 2050, the same may happen in the Congo Basin, the world’s second-biggest tropical rainforest.

Forests play a major role in fighting global warming, but the authors of the recent studies say we shouldn’t be overly reliant on them as a solution, given their diminished capacity to absorb carbon dioxide.

Instead, they say that cutting emissions is more urgent than ever.

The studies look at the links between rising temperatures and tree growth and mortality rates. Both studies use data from the International Tree-Ring Data Bank, the world’s largest public archive of this type, maintained by the U.S. National Oceanic and Atmospheric Administration (NOAA). The rings that appear in cross-sections of tree trunks provide crucial information about the individual tree’s age, growth rate, and the prevailing environmental conditions.

In 2015, Brienen had already observed a change in the dynamic of growth and mortality of Amazonian trees. He analyzed data collected in 321 different parts of the forest during the past three decades. “We label all the trees, identify the species and measure their diameters. Then we come back some years later, measure them again, calculate how fast they have been growing, how many new trees have been recruited, and how many trees are dying,” he says.

Looking at the data, Brienen realized that the trees grew faster in the 1980s and the 1990s. On one hand, that’s good news: the faster a tree grows, the more carbon it can take out of the atmosphere. But on the other hand, the faster a tree grows, the sooner it dies. “It is the ‘grow faster, die young’ phenomenon,” Brienen says. “If they grow too fast, they quickly reach a certain diameter and a certain height at which they die, because the leaves can’t pump all the water they need from the roots up to the canopy. Then they die of hydraulic failure.”

In the 1980s and 1990s, however, this trade-off between growth and mortality played in our favor. Accelerated growth made up for the trees’ early deaths when it came to the net amount of carbon captured. From 2000 to 2010, however, the situation began to reverse. “The increase in the growth rates have flattened, but the mortality rates continued to increase. It means that over recent times the forest is taking up less carbon from the atmosphere than it did before,” Brienen says.

Read the full article about tropical trees by Fernanda Wenzel at Mongabay.