The Forest for the Trees

Jan. 24, 2019

It’s no secret that water is becoming increasingly scarce. We’ve documented the land grab for water resources in California and the decreasing groundwater supplies for agricultural use throughout the Midwest. However, it seems that as temperatures warm, urbanization and agriculture are not the only areas impeded by water scarcity. The growth of trees in forests around the world is also becoming limited by water availability.

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A new study published in Science Advances outlines research conducted by the University of Arizona (UA) Laboratory of Tree-Ring Research and the Swiss Federal Research Institute WSL in Zurich.

The growth rings of a tree are naturally wider when conditions are better and narrower when conditions are worse. To evaluate the effect of climate on tree growth, a team of scientists compared the ring-width measurements of trees from 2,700 sites around the world during two time periods, 1930–1960 and 1960–1990.

The team also mapped average temperature, precipitation, and drought stress on plants for the two time periods on a grid. Correlating the tree-ring data with geographic map coordinates revealed that climate shifts and a decrease in water availability during the 20th century corresponded directly to the reduced ring-width measurements of trees worldwide.

“Our study shows that across the vast majority of the land surface, trees are becoming more limited by water,” first author Flurin Babst, who conducted the research, told Science Daily.

“Reduced growth is indicative of increased stress on plants—which can be linked to mortality,” 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.”

The team hopes that the integration of growth data from tree rings with climate data will help scientists understand how climate affects vegetation and improve digital models.
About the Author

Laura Sanchez

Laura Sanchez is the editor of Distributed Energy and Water Efficiency magazines.