by Zach St. George
W.W. Norton & Company, 2020
“More than any other living thing, trees define their surroundings,” Zach St. George writes in the opening of The Journeys of Trees: A Story About Forests, People, and the Future. “They break up the horizon, mark the trail, soften hard edges. You can pick them out, one by one…. Entire scenes can be conjured by the presence or absence of trees: the forest; the field; the house on the corner with the maple in the yard. A tree is a rooted thing, so a tree is also a place.”
Trees and forests, of course, cannot simply get up and move, so they face unique challenges in a rapidly changing climate. With a focus on five very different species of trees in very different circumstances – giant sequoia, ash, black spruce, Florida torreya, and Monterey pine – St. George outlines the challenges of forestry and conservation in the face of ongoing climate changes. He examines a series of questions. In a warmer world, how will “more stressed trees; hotter, deadlier drought; more insect outbreaks; [and] more fire” affect forests? What are people doing to help them? When should they stand back and do nothing?
As many foresters and landowners in the Northeast know, the scourge of ash trees is the emerald ash borer, which St. George calls “one of the most destructive invaders ever to hit North American forests.” The invasive beetle, which is believed to have arrived in Michigan in a wooden shipping pallet in 2001, has now reached 36 states, 5 Canadian provinces, and western Russia. The International Union for Conservation of Nature, which monitors species at risk of extinction, lists 16 ash species, with 1 (Carolina ash) endangered and 5 others – including white, blue, and black ash, which are native to the Northeast – as critically endangered.
St. George recaps other disasters accidentally caused by humans: the gypsy moth infestation, the chestnut blight, and the Dutch elm disease. Each has had long-lasting impacts on forests in the Northeast – and beyond. He describes invasive pests as “biological pollution” and notes that globalization has increased their frequency and that climate change has made it easier for some harmful insects and diseases to thrive.
The story of the ash is perhaps the grimmest in the book. St. George reports on the failures and very limited successes of quarantines, felling trees, and using biological controls in trying to save them. For the other trees, he writes about additional strategies, including assisted migration or colonization (transplanting trees to new areas) and assisted population migration (planting seeds from the best-performing southern trees to the north, within the existing range of the species). Both approaches are experimental, controversial, and come with risks, including the possibility of introducing unwelcomed insects and diseases to new areas. “This is not gardening,” ecologist Thomas Abeli told St. George. “I think assisted colonization should be strictly supervised by ecologists and conservationists.”
Although most of the book is about the present state of forests, St. George takes a long view, starting with evidence from the fossil record that shows truly ancient tree migrations, as well as numerous examples of how humans have managed forests – or not. Without any Lorax speaking for the trees, “management” has sometimes amounted to nothing more than deforestation. On the other hand, 2,000 years ago, the Romans brought stone pines to other parts of the Mediterranean and numerous trees and crops to the British Isles, including chestnuts, elms, pears, cherries, figs, and onions.
The Journeys of Trees presents some grim realities and re-emphasizes the threats of climate change; however, St. George repeatedly reminds us how much people appreciate and depend on trees. As he highlights efforts to help trees through climate change, he draws a picture of a symbiotic relationship in which people need trees and trees need people.