Identifying tree species can be challenging when the traits typically used to describe them—leaves, buds, and twigs—are not clearly visible or, in the case of leaves, not even present. Join Michael Wojtech on Saturday, June 25, from 9 – 1 in the Hunnewell Building at the Arnold Arboretum in Jamaica Plain for an exploration of bark, the tree characteristic that is always visible in every season. A copy of his new book, Bark: A Field Guide to Trees of the Northeast, is included with the class fee. You will learn how to differentiate six different bark types, how to use the book’s identification keys, and begin to discover why such a variety of bark characteristics has evolved—Why do some species have smooth bark, while on others it is thick and broken? Why does bark peel? After a classroom session we will practice identifying native tree species on the grounds of the Arboretum. Open to naturalists at all levels of experience.  $55 Arnold Arboretum members, $70 for nonmembers.  To register, visit http://my.arboretum.harvard.edu/Info.aspx?DayPlanner=1026&DayPlannerDate=6/25/2011.