Fast moving and not overly technical, the tale of "Witness Tree" takes us down the path of bio-geographic research, particularly as it pertains to trees. Long-lived as they are, today's trees are likely to encounter unprecedented conditions as they age. The story takes place at Harvard Forest in Petersham, MA, one of the most studied forests in the world. Much of the institution's historical research is at the center of today's inquiries into climate futures and, of course, the future of the world's vegetation. Researchers from multiple disciplines bring their specialties there, including some top-level canopy research by highly skilled tree-climbers.