Drought can set back tree growth for up to four years, study claims

Trees can take up to four years to recover from severe drought and resume their normal growth patterns, a US study has found.

Image: Lassen Volcanic National Park
Image: Lassen Volcanic National Park

Using the International Tree-Ring Data Bank, the researchers from a range of institutions analysed data of 1,338 forest sites mainly in North America and Europe.

They concluded that forests exhibit a drought "legacy effect" of three to four years' reduced growth following drought, during which time that are less able to act as a carbon sink. The effect was most pronounced in pine trees, though puzzlingly, some trees also showed a positive effect.

Leaves lost during a drought may impair growth afterwards, the paper says, and trees may also be left more vulnerable to pests and diseases.

Princeton Environmental Institute researcher and lead author of the paper Dr William Anderegg added: "We desperately need to assess if drought legacies occur in tropical forests too, which we weren't able to do in this study. Most tropical trees don't form tree rings, which makes tree ring analysis quite difficult."

Droughts are forecast to increase in frequency and severity as a result of climate change, he pointed out, suggesting that carbon absorption models may need to revised.

A 2005 study calculated that the 2003 drought in Europe led to a 30 per cent reduction in tree growth, giving a net loss of carbon to the atmosphere.

The current study is published in Science.

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