|May 15, 2019|
Climate change may make trees live fast and die young
|Everyone from governments to oil companies is looking at tree-planting as a way to counter global warming, but this strategy could be less effective than we thought.|
In a warming world with growing levels of carbon dioxide in the atmosphere, researchers have hypothesised that trees will grow faster. But this isn't necessarily a good thing. Faster-growing trees may live shorter lives, reducing the amount of time they lock carbon away for.
Now data is beginning to suggest that this is the case. Ulf Büntgen of the University of Cambridge and his colleagues have looked at tree ring records going back 2,000 years, and found that the longest-lived trees were those with the slowest growth rates.
"We find that if a tree grows fast in its initial stage, there is a high probability that it will die younger," he says.
The team studied 1800 trees, all of which were mountain pines from the Spanish Pyrenees or Siberian larch from the Russian Altai region, which can live up to about 800 years. In a warmer world with more carbon dioxide, however, these trees might live just 150 years after growing rapidly.
We should keep planting trees to tackle climate change, says Büntgen. But we should realise that, on a timescale of centuries, the carbon these trees sequester may not stay there as long, he says. We should also question whether the fast-growing poplars and willows currently favoured by tree-planting schemes are the best species to use.
"It doesn't mean that the carbon sink [of forests] will go away, just that we may not have as much as we thought," says Pep Canadell of CSIRO Climate Science Centre in Australia
The effect might be offset somewhat by increasing droughts wrought by climate change which could, in some places, stop trees from growing so fast.
For the time being, any reduction in the time carbon is stored in trees in the northern hemisphere is also being outweighed by other factors -- such as longer growing seasons -- which are increasing the carbon those forests hold now.
Simon Lewis of the University of Leeds, UK, says the new study could help inform climate models, but warns against making confident carbon cycle predictions on the basis of one analysis of two species.