Michael A. Dirr is a Professor Emeritus of horticulture at University of Georgia. He is widely acknowledged as one of the leading experts on trees and shrubs for landscapes and gardens. He holds BS and MS degrees in horticulture from Ohio State University and the PhD from University of Massachusetts. Dirr has introduced over 200 woody plants to cultivation and holds 29 patents with the UGA Research Foundation. 

Keith S. Warren, tree breeder and nurseryman, has significantly reshaped the tree palette of the American landscape through introduction and promotion of improved tree cultivars. As Director of Product Development for J. Frank Schmidt and Son Co., one of the world’s largest nurseries, he created an extensive tree evaluation program, testing virtually every new deciduous cultivar during his 40-year career.