Eric Waller

Photo of Eric Waller

“Satellite Data Reveal Unique Climate for Giant Sequoia”

Introduction by Brad Balukjian

The restriction of Giant Sequoia (Sequoiadendron giganteum) to the southern Sierra Nevada has long puzzled ecologists, as an appropriate climate appears to exist in the northern Sierra. Custom-developed cloud cover climatologies from AVHRR and MODIS satellite imagery demonstrate that Giant Sequoia environs in the southern Sierra are among the cloudiest of California over the course of a year, and are the cloudiest on March and April afternoons. Cloud frequency predicts Sequoia distribution far better than any other climatic variable regardless of statistical model. MODIS land surface temperature data reveal that the Sequoia belt also has unusually low diel temperature range, even on clear days. Meteorological data from 55 meter towers confirm this pattern, showing unusually low spring maximum temperatures, and relative humidity regularly peaking in the afternoon. Climatological data don’t capture these patterns due to the sparse network of surface-influenced stations in the rugged Sierra Nevada. Evidence from satellite derived information has also been historically hindered, with errant classification of higher elevation snow cover in the Sierra as cloud in formal cloud-mask products contaminating the signal of true cloud cover over the lower elevation Sequoia belt. It appears that the high frequency of cloud cover in the area is a result of regional pooling of cold and moist air aloft, often in combination with local transport of water vapor through convection. The extent to which Giant Sequoia is dependent on this cloud cover for its reduction of water deficit, delaying of snowmelt, or increasing of diffuse vs. direct light, or is dependent on the many other related aspects of the unique environment is yet to be determined.

One of my best memories in ESPM is the Kremen lab vs. Brashares lab dance-off at the past graduate symposium.

I would like to thank my committee of Dennis Baldocchi, Max Moritz, and David Ackerly, as well as the many wonderful graduate students, researchers, and staff whom I’ve had the pleasure of interacting with over the years.