Hemlock: A Forest Giant on the Edge ed. by David R. Foster (review)

If a famous tree could tell us its story and offer its wisdom, it might read something like Hemlock. Few trees or stands of trees in the world might merit such a book-length biography, and the arc of many of those biopics could perhaps trace the relation of a tree to the development of a religion. Just as a hallowed fig tree in Bodh Gaya could shed light on the birth of Buddhism, or groves of olive trees around Jerusalem could add color to the chapters of early Christianity, there exists a set of hemlock stands in central New England that offer witness to a budding science of resiliency. Fusing forestry, biogeography, environmental history, and ecology, Hemlock brings scientific enlightenment that casts its light far beyond the cathedral-like canopies of its subjects on the Harvard Forest in central New England. Indeed, these trees, and their interlocutors at Harvard Forest tell a tale that we all would do well to hear as we contemplate the Anthropocene.

Devoid of the typical trappings and jargon of academic literature, this creatively structured and carefully edited book cleanly reads as a general-audience oriented story of curiosity and discovery. Those of us with an academic bent to their reading will be thankful that the team of Harvard Forest-based authors have also penned a parallel set of highly useful and engaging bibliographic essays. I certainly encourage you to read (and perhaps assign to your students) both these parallel stories within this fascinating, timely, and gorgeous book. To help you decide whether to spend some time with Hemlock, my review proceeds by answering three questions that you may have: First, why hemlock? Second, why read this book now? And finally, in telling the story of a species whose range covers much of eastern North America, what is gained by focusing on just several stands of hemlock in central New England?

Surely, Hemlock is partly homage to the tree itself. Beautiful and ecologically important, eastern hemlock (Tsuga canadensis) is an old friend to those of us who love the forests of eastern North America. Its shady evergreen canopy forms forest cathedrals on streambanks and mountaintops from Nova Scotia to Alabama and Maryland to Minnesota. As described in rich scientific and poetic turns (including a lovely chapter epigraph from Longfellow) within the book's second chapter, David Orwig summarizes reams of scientific literature documenting how the special adaptations of hemlock set it apart from other species in the eastern forest. For instance, he describes how hemlocks fundamentally alter the physiology of their ecosystem, often in fascinating and paradoxical ways. By being miserly with their water loss, hemlocks create wet environments that hold snow and water in their deeply shaded and rich forest floor. In the fifth chapter, Aaron M. Ellison and Benjamin H. Baiser convincingly argue that all these adaptations make hemlock a foundation species, which, if lost, would fundamentally change the ecosystem. And this is crucial, because this is exactly what is happening.

The book's subtitle, A Forest Giant on the Edge, points toward the ongoing range-wide decline of hemlock at the hands, or indeed the stylet, of the parasitic hemlock woolly adelgid insect. Since it hitched a ride across an ocean and a continent in 1951 on a Japanese hemlock bound for a tree nursery in Virginia (p. 124), this invasive insect has spread rapidly, infesting and killing hemlocks from Maine to Georgia. Especially as climate change reduces the frequency of cold winter temperatures that can slow the insect's march, we do not know of any way to stop its spread.

Many have lamented the loss of the hemlock, and the book's editor, David Foster writes a thoughtful lament in the epilogue. This bookends nicely with Hemlock's forward, an entertaining piece written by Robert Sullivan, sections of which also appeared in the top environmental...