On the cover: David Wedin, University of Nebraska forest ecologist, inspects a pine seedling before planting it in a research plot at the 25,000-acre Nebraska National Forest near Halsey. The world's largest planted forest is a unique laboratory for studying the implications of widespread tree planting or encroachment on native grasslands. Wedin's team is studying what happens to grass production, soil moisture, groundwater recharge and carbon storage as tree density increases. See stories on pages 6 and 7.

Cover photo by Brett Hampton