The Long-Term Ecological Research (LTER) program, sponsored by the National Science Foundation, monitors ecological phenomena in a range of environments. The program supports 16 sites in North America and two in Antarctica, including the newest site in the McMurdo Dry Valleys—one of the most extreme deserts on Earth. The McMurdo LTER, headed by Dr. Robert Wharton, Jr. (Desert Research Institute), is the coldest and driest site. The study attempts to understand two processes: the influence of physical and biological constraints on dry valley ecosystems, and the effects of material transport on these ecosystems.