Climate Change: Drought May Cause Large Trees to Die First

Drought is still a major issue as the climate continues to change. Now, scientists have found that drought has had a more detrimental impact on the growth and survival of larger trees. In addition, while the death of small trees may affect the dominance of trees in a landscape, the death of large trees has a far worse impact on the ecosystem.

"Previous studies at a few sites had shown that large trees suffer more than small trees during and after droughts, and our theory suggested this should be a globally consistent pattern, but this project was the first to test this hypothesis globally," said Nate McDowell, one of the researchers, in a news release.

Living trees soak up greenhouse gases and then store it for long periods of time in their woody tissues. Dying trees, though, release it. This carbon sink then becomes a carbon source.

Not only that, but larger trees release more water into the atmosphere, cooling the land and supporting cloud formation. This, in turn, affects how much solar radiation is reflected back to space and impacts precipitation. These large trees also play a role in biodiversity, creating environments on which many plant and animal species are dependent.

In this latest study, the researchers analyzed 38 forests worldwide, and the experiment itself included both natural and experimental droughts. The researchers accounted for standard growth and mortality rates, and analyzed tree size-related variation responses based on diameter growth and death under drought and normal conditions.

So what did the researchers find? It turns out that drought-related death increased with tree size in 65 percent of the droughts examined.

The findings show that as droughts increase, the increased deaths of large trees could be a major issue. It also shows that large trees will suffer the most from a warming climate, drier soils and more severe drought stress.

The findings are published in the journal Nature Plants.

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