In the early years of the 20th century an introduced fungal blight killed an estimated 4 billion American chestnut trees, effectively eliminating what had been a foundational species of eastern North American woodlands.  Scientist Andrew Newhouse of the State University of New York explains how his university is preparing to release a race of American chestnuts genetically engineered to withstand the blight, so that this essential tree may flourish in the forest once again.