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Mountain trees could help stabilize climate over millions of years

10 February 2014, by Harriet Jarlett

Tree roots in mountainous regions can help to regulate long term global temperatures, say scientists.


A new study, published in Geophysical Research Letters, shows that if global temperatures were to rise over geologic timescales, trees at higher elevations could play an important role in encouraging more carbon dioxide to be removed from the atmosphere.

The team, from the Universities of Sheffield and Oxford, conducted their research in the Peruvian mountains, where they found that in higher, colder conditions tree root growth slows. This means the roots don't reach far enough into the ground to cause the rocks beneath them to break down and combine with carbon dioxide, removing it from the atmosphere - a process called weathering.

But if global temperatures were to rise, then the layer of organic material between the root and the rocks would rot more quickly and so get thinner, allowing the roots to reach the rock and begin the weathering process.

'If the world gets warmer, as it would during a large volcanic event, decomposition of the organic layer would accelerate, and the organic layer would become thinner,' explains Dr Chris Doughty of the University of Oxford, lead researcher on the project. 'Instead of growing into the organic layer, as they do now, tree roots would grow into the area near the rock, breaking it down to release calcium and magnesium ions which would combine with carbon dioxide – effectively pulling the CO2 out of the air.'

Mountainous areas are also important as they are made of volcanic material such as granite and basalt. These contain more calcium and magnesium than the sediments found in lowlands so will have an even greater effect on carbon dioxide levels.

'There are several mechanisms where life basically stabilized the climate for life, we think that this is one of those mechanisms. It is important because it helps us to better understand how life has maintained itself on this planet for so long,' Doughty says.

The team measured the amount of roots that grew into the ground, and how thick the layer of organic matter was between the surface and the bedrock.

To measure root depth they placed mesh bags of root free soil into the ground. After three months they dug these bags up and measured the number and weight of roots which had penetrated them. The researchers then used computer models to calculate the amount of carbon likely to be pulled out of the atmosphere through weathering if the Earth became very hot.

'This is too slow a process to have any noticeable effect on the carbon dioxide people are adding to the atmosphere by burning of fossil fuels. Over millions of years, the increased carbon dioxide will accelerate weathering, but this will not help humans deal with anthropogenic climate change unfortunately,' he concludes.

Doughty, C. E., L. L. Taylor, C. A. J. Girardin, Y. Malhi, and D. J. Beerling (2014), Cenozoic global change possibly stabilized by montane forest root growth and soil organic layer depth, Geophys. Res. Lett., 41, doi:10.1002/2013GL058737.

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