Water, not temperature, limits global forest growth as climate warms

ScienceDaily | 1/16/2019 | Staff
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The effect is most evident in northern climates and at high altitudes where the primary limitation on tree growth had been cold temperatures, reports the team this week in the online journal Science Advances.

"Our study shows that across the vast majority of the land surface, trees are becoming more limited by water," said first author Flurin Babst, who conducted the research at the UA Laboratory of Tree-Ring Research and the Swiss Federal Research Institute WSL in Zurich.

Time - Anybody - Tree - Growth - Responses

"This is the first time that anybody has projected the tree growth responses to climate at a near-global scale," Babst said.

The researchers compared the annual growth rings of trees during two time periods, 1930-1960 and 1960-1990. The growth rings are wider when conditions are better, narrower when conditions are worse. The ring-width measurements were taken from trees at about 2,700 sites spanning every continent except Antarctica.

Time - Periods - Team - Temperature - Precipitation

For those two time periods, the team also mapped average temperature, precipitation and measures of drought stress on plants onto a grid covering the world's temperate and boreal regions.

Adding tree-ring data to the map allowed scientists to see whether the changes in climate during the 20th century corresponded to the changes in growth of the world's trees.

Co-author - David - Frank - Areas - Part

UA co-author David Frank said, "We saw areas where, in the earlier part of the 20th century, temperature limited growth. But now we are seeing shifts towards moisture-drought limitation."

Comparing 1930-1960 with 1960-1990, the average temperature increased 0.9 degrees F (0.5 degrees C) and the land area where tree growth was primarily limited by temperature shrank by 3.3 million square miles (8.7 million square kilometers), an area about the size of Brazil.

Babst - Change - Temperature - Area - Trees

Babst was surprised that such a small change in temperature would shift such a large area of trees from being temperature-limited to being water-limited.

"That's much more than I expected," said Babst, who is...
(Excerpt) Read more at: ScienceDaily
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