Buckthorn is the most common tree in the Chicago Region, making up approximately 40 percent of our canopy (source: 2010 tree census by the U.S. Forest Service and The Morton Arboretum).
The Lake County Forest Preserve has provided these brochures to suggest the replacement native plantings/seedings of Buckthorn:
Brochures:
Invasive Hedge and Screen Replacement Guide
Links:
Chicago Region Trees Initiative