â€œWe are doing some repair work on the systems that measure the sap flow through the tree.â€
How do you measure the water consumption of a 350-foot-tall redwood tree? By installing tiny sap flow sensors into the outermost layers of the treeâ€™s woodthe sapwood. Welcome to Pulse of the Planetâ€™s Science Diaries, a glimpse of the world of science from the inside. Marie Antoine [ANN-twon] and Anthony Ambrose are working with ecologist Steve Sillett in Californiaâ€™s redwood forests.
MA: â€œWe’ve just gotten down to the bottom of the tree and that scraping sound is the sound of Anthony enlarging a small hole in the bark, and then he’s going to drill three tiny holes into which the sap flow probes will be placed.â€
AA: â€œThese sap flow probes work by way of two sets of thermo couples that surround on the upstream and downstream sides of the sap wood. And there’s a heating element that’s put in the center. And periodically it gives off a little heat pulse, and the thermo couples measure the change in temperature. The magnitude of that change is dependent on the rate of flow of the water through the sap wood. These sap flow probes are very sensitive to changes, and they’re able to detect changes in direction as well as the magnitude of flow. So we can tell when water is going up the tree from the roots to the foliage, as well as when there’s water flowing down the opposite direction. Coast redwoods have a remarkable ability to absorb water condensed from fog on their foliage, so that they can take in water from both the soil as well as the atmosphere.â€
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Pulse of the Planetâ€™s Science Diaries are made possible by the National Science Foundation. Iâ€™m Jim Metzner.