Giant sequoias are the largest trees on Earth by mass, and some are more than 3,200 years old. While they’ve survived drought, fire, and disease for centuries, climate change is making these threats more intense and harder to withstand.

Much of the research on sequoias has focused on the above-ground critical zone (CZ) - the part of the environment that includes tree canopies and leaves. But during times of drought, what happens below ground becomes just as important. Water uptake begins in the subsurface CZ, which includes soil, weathered rock (saprolite), and bedrock. Understanding this zone is key to uncovering how sequoias find and use water.

In Yosemite’s Mariposa Grove of Giant Sequoias, we use ground-penetrating radar and seismic refraction to 'look' underground without digging. These tools help us map root systems, and determine soil thickness and subsurface structure. We want to know: How deep do sequoia roots go? Do sequoias depend more on shallow soil water, water in weathered rock, or from bedrock moisture? Can this information help make more informed strategies for long term sequoia management and protection?