Giant sequoias are the largest tree by mass on the planet, and have been around since the start of the Bronze Age ~3200 years ago. They have shown incredible resilience to drought, disease, and fire - all of which are becoming more frequent and intense with worsening climate change. 

Along the southeastern boundary of Yosemite National Park, the ~250-acre Mariposa Grove of Giant Sequoias is home to over 500 mature sequoias, two of which are among the 30 largest in the world. The key to their survival lies in the subsurface, and how roots and water are distributed below ground. Subsurface moisture is a critical aspect of sequoia growth and life (Muir 1901, Rundel 1972).

Currently, roots are thought to go no deeper than 1m (Hartesveldt et al. 1975), although the trees themselves can weigh up to 2.7 million pounds (NPS). This constrains their 600-800 gallon daily summer water requirements to the first three feet of the subsurface. But, is it possible roots go deeper than this? Beyond the soil and into fractured bedrock, perhaps?

My work aims to image the unexplored subsurface beneath the giant sequoias using (1) Ground Penetrating Radar and (2) Seismic Refraction to visualize root structures, determine subsurface porosity, and map lateral soil depth variability. 

The 3D grid and accompanying analysis will provide a more complete picture of how these ancient trees interact with their subsurface environments. Using seismic refraction data will also enable us to position roots in the context of subsurface weathering, which will build upon work by Muir 1901 and Rundel 1972 that currently constrains water uptake to be occurring in just moist soil layers. 

A clearer understanding of how sequoia roots access moisture in changing conditions is critical for predicting their resilience and informing adaptive management strategies. This knowledge can guide forest and managers in identifying groves that may be more susceptible to climate stress, and assess where targeted interventions such as prescribed burns, irrigation trials, or soil moisture monitoring could be applied.