Global warming will reduce the amount of carbon stored in forests, warns a new study.
Scientists say 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 boosts annual tree growth but slashes their lifespan.
The overall result, they claim, is a reduction in the amount of carbon stored in forests as it returns to the environment when they die.
Carbon from plants and trees enters into the carbon cycle when they die and this eventually manifests itself as carbon dioxide – a greenhouse gas.
Cambridge University scientists found that as temperatures increase, trees grow faster – but they also tend to die younger (stock)
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 carbon dioxide 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.
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 (stock image)
For the current study, Professor Büntgen along with colleagues from Germany, Spain, Switzerland and Russia, 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.
The idea of a carbon residence time was first put forward by co-author Professor Christian Körner, of the University of Basel in Switzerland, but the study is the first time that it has been confirmed by data.
The link between growth rate and lifespan is comparable to the relationship between heart rate and lifespan seen in the animal kingdom, explained the researchers, as animals with quicker heart rates tend to grow faster but not live so long.
Professor Büntgen added: ‘We wanted to test the ‘live fast, die young’ hypothesis, and we’ve found that for trees in cold climates, it appears to be true.
‘We’re challenging some long-held assumptions in this area, which have implications for large-scale carbon cycle dynamics.’
The full findings were published in the journal Nature Communications.
WHAT CAN TREE RINGS TELL US?
Trees can live for hundreds—and sometimes even thousands—of years.
Over this long lifetime, a tree can experience a variety of environmental conditions: wet years, dry years, cold years, hot years, early frosts, forest fires and more.
Concentric rings in tree trunks tell us how old the tree is, and what the weather was like during each year of the tree’s life.
The light-coloured rings represent wood that grew in the spring and early summer, while the dark rings represent wood that grew in the late summer and fall. One light ring plus one dark ring equals one year of the tree’s life.
Because trees are sensitive to local climate conditions, such as rain and temperature, they give scientists some information about that area’s local climate in the past.
Concentric rings in tree trunks tell us how old the tree is, and what the weather was like during each year of the tree’s life. One light ring plus one dark ring equals one year of the tree’s life
For example, tree rings usually grow wider in warm, wet years and they are thinner in years when it is cold and dry.
If the tree has experienced stressful conditions, such as a drought, the tree might hardly grow at all in those years.
Very old trees can offer clues about what the climate was like long before measurements were recorded. This field—the study of past climates—is called paleoclimatology.
Paleoclimatologists rely upon natural sources of climate data, such as tree rings, cores drilled from Antarctic ice and sediment collected from the bottom of lakes and oceans. These sources, called proxies, can extend our knowledge of weather and climate from hundreds to millions of years
Combined with weather and climate information from satellites, they can help scientists model major climate events that shaped our planet in the past.
And these models can also help us make predictions about what climate patterns to expect in the future.