Animation shows Earth ‘breathing’ carbon

Global warming will reduce the amount of carbon stored in forests, according to a 2019 study in Nature Communications.

Scientists said it is down to the fact that trees tend to ‘live fast and die young’ in the world’s continually warming climate. 

The research team, led by Cambridge University scientists, said that increasing temperatures boost annual tree growth but slash their lifespan. 

The overall result, they said, is a reduction in the amount of carbon stored in forests as it returns to the environment when they die.  

Warm temperatures provide ideal growing conditions for trees which the researchers believe doesn’t prepare the plant for adversity.

They say the lack of ‘toughening up’ often leads to the trees perishing when those grown in cooler climates would survive. 

The researchers said their findings have implications for global carbon cycle dynamics and, ultimately, the amount of CO2 in the atmosphere. 

As the Earth’s climate continues to warm, they say tree growth will continue to accelerate, but the length of time that trees store carbon – the so-called ‘carbon residence time’ – will diminish.

During photosynthesis, trees and other plants absorb CO2 from the atmosphere and use it to build new cells.

The research team explained that long-living trees, such as pines from high elevations and other conifers found across the high-northern latitude forests, can store carbon for many centuries.

Study lead author Professor Ulf Büntgen, of Cambridge University’s Department of Geography, said: ‘As the planet warms, it causes plants to grow faster, so the thinking is that planting more trees will lead to more carbon getting removed from the atmosphere.

‘But that’s only half of the story. The other half is one that hasn’t been considered: that these fast-growing trees are holding carbon for shorter periods of time.’

Professor Büntgen uses the information contained in tree rings to study past climate conditions.

He explained that tree rings are as distinctive as fingerprints: the width, density and anatomy of each annual ring contains information about what the climate was like during that particular year.

By taking core samples from living trees and disc samples of dead trees, scientists are able to reconstruct how the Earth’s climate system behaved in the past and understand how ecosystems were, and are, responding to temperature variation.

For the study, Professor Büntgen and colleagues sampled more than 1,100 living and dead mountain pines from the Spanish Pyrenees and 660 Siberian larch samples from the Russian Altai. Both are high-altitude forests that have been undisturbed for thousands of years.

The researchers used the samples to reconstruct the total lifespan and juvenile growth rates of trees that were growing during both industrial and pre-industrial climate conditions.

They found that harsh, cold conditions cause tree growth to slow, but they also make trees stronger, so that they can live to a great age.

But trees growing faster during their first 25 years die much sooner than their slow-growing relatives.

The negative relationship remained ‘statistically significant’ for samples from both living and dead trees in both regions, according to the findings.