Tall trees in the Amazon face an uncertain future

Climate change has increased temperatures across the world, affecting the most ecologically important regions such as the Amazon rainforest. 

The International Panel on Climate Change (IPCC) Sixth Assessment Report, highlights increasing concerns for the Amazonian forests. If greenhouse gasses (GHG) and CO2 emissions double by 2050, maximum temperatures in the Amazon will likely exceed 35 degrees Celsius at least 150 days a year by the end of the century.

A recent study published in the journal Nature Communications led by researchers at the University of Helsinki elaborates on how climate change impacts these ecosystems. 

The study used measurements from terrestrial scanning LiDAR which allowed researchers to track how different layers of the forest are affected by the changing environmental conditions caused by climate and fragmentation. 

Tall trees in Central Amazonia are impacted by maximum temperatures of the understory (the underlying layer of vegetation in a forest or wooded area)  above 35 degrees. This is because the canopies of old-growth forests provide shade and buffer high temperatures. 

When the temperatures in underlying layers reach 35 degrees, some trees are impacted by water stress, which reduces leaf development. As a result, the tall trees start to shed their leaves and branches. While 35 degrees (95 degrees fahrenheit) may seem like a reasonable climate for the Amazon, only the months of August and September usually reach that level of heat in normal conditions.

“If the number of days registering these very high temperatures inside the forests also increases, we might see that the tall trees will suffer considerably,” explained study lead author Matheus Nunes.

The risks to the Amazon rainforest aren’t limited to climate change, but are further exacerbated by deforestation. The study also revealed a feedback loop between deforestation and warming temperatures.  

Reduced tree cover allows more light to penetrate the forest, leading to hotter temperatures in the understory. The hotter temperatures add further pressure on the tall trees, causing trees to shed their leaves and branches for a prolonged time. 

More research is needed to better understand how tropical ecosystems respond to climate change. There remain uncertainties between  the timing and causes of seasonal events, such as leaf shedding and burst. 

Despite these uncertainties, the study demonstrates the complexity of climate variations on taller trees and highlights the effects of climate and human disturbance on the Amazonian rainforest. If deforestation continues and forests become more fragmented, severe consequences will follow, and we can expect to see a large-scale shift in the way tropical ecosystems breathe.

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By Katherine Bucko, Earth.com Staff Writer