The Great Plains face a surprising threat: Too many trees

To really understand what’s going on in the Nebraska Sandhills, Shelly Kelly told me, it’s helpful to see it from the air. From the window of her father’s Bonanza A36, we looked out over the heart of one of the most rural landscapes in the United States. The Sandhills are a 19,500 square-mile swath of grassy dunes embellished with grazing cattle, serpentine rivers, and sunflowers. Kelly has spent her life on the prairies of the…