In 2013 he was awarded the Veitch Gold Medal by The Royal Horticultural Society “in recognition of services given in the advancement of the science and practice of horticulture.” He has worked on numerous aspects of botany, horticulture and ecology over the past forty years. His interests are wide ranging and include such subjects as plant exploration in China, the root systems of woody plants, the natural and cultural history of the Ginkgo tree, and most recently urban ecology and vegetation, which is the subject of the recent book, Wild Urban Plants of the Northeast: A Field Guide (Cornell University Press, 2010). He has lectured widely in North America and Europe and has authored more than 130 scientific and popular articles.