Tropical forests can handle the heat, up to a point

By Richard B. Primack

“What though the woods be cut down, this emergency was long ago foreseen and provided for by Nature.”  

-Henry David Thoreau in his Journal.

Tropical forests face an uncertain future under climate change, but new research published in Science suggests they can continue to store large amounts of carbon in a warmer world, if countries limit greenhouse gas emissions.

Our research group contributed data from long-term forest plots in Malaysian Borneo to this international research project that evaluated over half a million trees in 813 forests across 24 tropical countries. In these plots, trees were measured every few years for their diameters and heights to determine growth rates.  This allowed our team to assess how much carbon is stored by forests growing under different climatic conditions today.

Location of plots used in this study.

We showed that tropical forests continue to store high levels of carbon under elevated temperatures, demonstrating that in the long run these forests can handle heat up to an estimated threshold of 32 degrees Celsius (90 degrees Fahrenheit) in daytime temperature; above this temperature, growth slows, trees die, and carbon storage declines. This carbon storage is an important ecosystem service in the fight against global climate change.

Increasing temperature results in a decline of tree growth rates.

Yet this positive finding is only possible if these species-rich forests have time to adapt, they remain intact, and if global heating is strictly limited to avoid pushing global temperatures above the 32 degrees Celsius (90 degrees Fahrenheit) threshold. The key actions needed are limiting the emission of greenhouse gases and protecting forests against uncontrolled logging and conversion of forests to agriculture and plantations. 

Measuring a tree for its diameter in a long-term plot at Bako National Park in Malaysia.

The paper Long-term thermal sensitivity of Earth’s tropical forests is published in Science 22 May 2020 (Embargo 21 May 19:00 BST/ 14:00 ET) (DOI: 10.1126/science.aaw7578).