Warmer temperatures can harm tall trees in the Amazon

High maximum temperatures impact tall trees in Central Amazonia, causing them to shed their leaves and branches.

Deforestation and fire are causing Amazon forests to become increasingly fragmented. A new study published in Nature Communications, guided by researchers at the University of Helsinki in collaboration with scientists worldwide, employs a novel approach to quantify the effects of fragmentation on plant phenology. The study depicts the annual life-cycle events in plants, beginning with budburst and leaf expansion and ending with leaf and branch fall. 

The researchers were able to track how different layers of the forest area were affected by changing environmental shapes caused by climate and fragmentation thanks to detailed measurements from terrestrial scanning LiDAR. 

The effects of global warming on Amazonian forests

According to the IPCC's Sixth Assessment Report, if very high greenhouse gas (GHG) and CO2 emissions double from current levels by 2050, maximum temperatures in the Amazon will likely exceed 35 degrees Celsius at least 150 days per year by the end of the century. 

The study, published in Nature Communications, explains why this is bad news for the Amazon rainforest. The study found that maximum understory temperatures above 35 degrees Celsius affect tall trees in Central Amazonia.

Many regions of the Amazon experience very high maximum temperatures above 35 degrees in August and September. The canopies of old-growth, intact forests usually buffer against the high temperatures observed in the understory. However, when the temperatures in these underlying layers reach 35 degrees, the tall trees shed their leaves and branches.

"If the number of days with these very high temperatures inside the forests increases, we may see that the tall trees suffer significantly," says postdoctoral researcher Matheus Nunes, the study's lead author.