Leaves of Absence
For millennia, forests have migrated to survive. Will climate change outpace their ability to adapt?
Review by Robin Tatu
The Journeys of Trees: A Story about Forests, People, and the Future
By Zach St. George.
W. W. Norton, 2021.
256 pages.
Woodlands are restless entities. While individual trees remain rooted, their collective copses retreat from hostile environments—be they Holocene ice sheets or fire-prone modern California—toward more nurturing habitats, one dropped seed and hardy sprout at a time. Studying fossils, researchers now can track tree-range migration, work that anchors science journalist Zach St. George’s absorbing portrait of resilience, climate change, and conservation. Since their beginnings, he writes, trees have “shuffled back and forth across continents,” sometimes following the same route more than once. Yet today, they may not be moving fast enough to survive. Should they fail, ecosystems across the globe could follow, imperiling the survival of our own species.
The Journeys of Trees takes readers on treks to Alaska, Michigan, and New Zealand, tracing the evolving paths of ancient forests from fossil remains and exploring modern groves of dying ash trees, stressed sequoias, and delicate hybrid saplings intended to revive the near-extinct American cedar. This lively blend of travelogue and science is informed by deep research. As St. George interviews academic, government, and industry experts who study the world’s forests, it becomes clear that warming temperatures, multiplying fires, and rising activity of beetles and borers are all taking a heavy toll. Even the fire-resistant California sequoias are now succumbing to wildfires while failing to produce enough new seedlings for successive generations. Given the prospects, St. George asks, what are the possibilities of human-assisted tree evolution? Who is doing the research, and what are the potential dangers?
The narrative opens with the historical sweep of human-assisted arboreal movement from 1500 BCE, when Egyptians imported frankincense trees for their valuable fragrant resin. Another significant effort dates from the late 1800s, when the New Zealand government, alarmed at the loss of timber sources after English settlers cleared local forests for sheep and cattle farms, began experimenting with tree imports from around the world. California’s Monterey pine, Pinus radiata, proved ideal, hardy and quick to reach maturity for commercial harvest. New Zealand’s success inspired radiata pine plantations in Australia, Spain, and Chile. Today, Monterey pine transplants cover an area 500 times greater than that of wild trees.
Imports can harm local ecosystems, however. Indeed, American tree species have fallen prey to fungus carried by beetles on Chinese chestnuts, while Dutch elms and East Asian ash devastated their native counterparts. Gene modification could offer these endangered indigenous tree species a potential lifeline. In New Hampshire, for instance, the US Forest Service currently is cultivating blight-resistant chestnuts—the result of several decades of crossbreeding the hard-hit American tree with hardier Chinese varieties. In California, Sierra Pacific Industries oversees the Giant Sequoia Genetic Conservation Plan to collect, plant, and monitor seeds from 70 genetically distinct sequoia groves, some located hundreds of miles north of the originals. St. George calls the program a textbook example of carefully planned and orchestrated assisted migration.
While investigations into assisted evolution are increasing—including by the National Park Service, which in 2019 began a set of risk-assessment guidelines for movement of species such as the bull trout, blue butterfly, and giant sequoia—actual projects remain small and few and the concerns significant. Ecologists interviewed in this book express appreciation for the passion of activists planting or moving trees. But they stressed the need for great caution. A tree placed in the wrong spot can become invasive and overwhelm local populations or harbor destructive pests. In monoculture plantations, imports can reduce rather than increase biodiversity.
While St. George acknowledges the risks and shortcomings of intervention, he believes that bold measures are required if forests are to have a future. Trees have served humans well, providing “raw materials, fuel, fruit, shade, and habitats for other species,” he writes. “They slow erosion, dull the wind, produce oxygen, and store carbon.” Trees also offer beauty and solace. For the author, this is timber worth fighting to preserve.
Robin Tatu is Prism‘s book editor.
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