What do old trees tell us about future water?

Trees respond to water like all living things, and they make useful records of dry and wet seasons. When it’s wet, the trees flourish. When it’s dry, they’re stressed. All those responses show up in a tree’s rings. Using those ring records, dendrochronologists have been able to take a look back in time and get a sense of water and drought in the West. Last month, scientists at Utah State University, Brigham Young University and The U.S. Forest Service announced they’d traced the Bear River’s stream flow back 1,200 years. That’s long before Mormon pioneers started building the first towns and cities in the area, and longer than any other tree-ring record in northern Utah to date. “One of the key messages is there is no ‘normal,’” said Roger Kjelgren, a professor and plant scientist at USU. “(Northern Utah) really is like a grandfather clock. It oscillates back and forth, moving between orbiting around a dry period and then shifting and oscillating back to a wet period.” The trick is lining up all that wet-dry variation with climate models. Climate models do a good job at predicting temperatures, but they’re not as good at predicting future precipitation. That’s where the trees can help. “I wouldn’t say it’s a match made in heaven, but it’s kind of a jigsaw-puzzle fit, taking the past tree record from the tree rings and combining it with the climate models to get an idea of these cycles,” Kjelgren said. During a wet season, trees drink in water and grow proportionally. As the season dries, they harden and cell walls get darker. That’s how tree rings form. During dry years, the rings will be tiny, sometimes requiring a microscope to see. The Bear River tree-ring study went back 1,200 years with the help of Utah juniper trees, a particularly finicky and telling species when it comes to water...more