"Flying over Oregon's woodlands, tree health specialist Danny DePinte was stunned by what he saw: a stretch of dead fir that seemed to go on and on.
"As we continued to fly along, it just kept going. It didn't stop for miles and miles," DePinte, who conducts research in the Pacific Northwest region for the U.S. Forest Service, told NPR.
Since 1947, the U.S. has been conducting annual aerial surveys across the country to monitor the health of trees. Flying up to 2,000 feet in the air, observers scan terrain in a grid-like pattern, analyzing about 30 acres per second, DePinte said. With a tablet, a pen and a trained eye, they are able to spot and diagnose unhealthy trees based on their color, posture and fullness."