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Helping Forests Migrate

March 7, 2017


A few weeks ago I had coffee with Connie Barlow, an author of popular science books (including The Ghosts of Evolution, 2002), as she and her partner Michael Dowd stopped in Santa Rosa en route southward. Among other things, we talked about the human-assisted migration of trees in response to climate change. I didn’t know much about the topic before, but have done a little reading recently at Connie’s behest, and the subject seems worth exploring in an essay.

Here, in short, is the argument for helping forests migrate:

  1. Trees and forests are important. Trees are vital to most terrestrial ecosystems, they hold soil and water, they produce oxygen, and they are key to the future survival of humans.
  2. Climate change is leading to shifts in rainfall and climate zones, resulting in threats to many important tree species in their current growing ranges.
  3. Unlike many other organisms, trees can’t move very quickly. If we figure a 30-year average generation time from seeding to reproduction, and an annual seed dispersal and fertilization range of a few miles at most (much less than a mile in most cases), then forests can migrate only a few miles per decade at best. But many climate zones are moving faster than that, putting forests and in some cases entire tree species at risk. (Topography is important: forests growing on mountainsides can often migrate to a new climate zone just by shifting a relatively short distance uphill; for flatland forests, that’s not an option. Geography is important too: some forests exist as islands in a sea of roads, buildings, and other impassable human infrastructure, making unassisted migration nearly impossible.)
  4. Assisted migration is feasible. What’s required are a rough idea of what the climate is likely to be in 30-60 years, and the human and economic resources needed to plant a large number of trees of a selected species in a region where future conditions will be to its liking.

The idea of assisted migration has been around for a while now. Carl Zimmer wrote a key article on the subject (addressing not just trees but other species as well) in the New York Times in 2007; as he noted, the subject is not without controversy. Old-line conservationists have argued against assisted migration, using arguments that I mostly agree with. Such efforts could take time, resources, and attention away from climate change mitigation and the conservation of remaining wilderness areas. Further, climatologists and conservationists can only make rough predictions about future habitats and future relationships among species within those changed habitats. The unknowns are staggering. Humanity has already sown havoc in ecosystems worldwide by deliberately or inadvertently introducing non-native species. Might well-intended efforts to save endangered forests through assisted migration end up creating as many problems as the similarly well-intended introduction of cane toads into Australia?

Further, for me the idea has some unpleasant associations. Emma Marris discussed assisted migration approvingly in her 2011 book Rambunctious Garden; she is sometimes characterized as an eco-modernist (other eco-modernists—also sometimes called eco-pragmatists or “bright greens”—include British author Mark Lynas along with Ted Nordhaus and Michael Schellenberger of the Breakthrough Institute). Marris and the eco-modernists have been opposed by critics such as conservation biologist E. O. Wilson, who are skeptical of claims that the continued growth of human numbers and consumption rates is compatible with the survival of natural systems. I was present at a debate between Marris and Wilson at the Aspen Environment Forum in 2012 (I publicly debated Lynas at the same gathering); in my view, Wilson made by far the stronger case, arguing that the world’s last wild places really do require and deserve extraordinary defense (to Marris, everyplace is nature, including the shopping mall, so what’s the big deal?). “Where do you plant that white flag you’re carrying?”, he famously asked Marris. In their 2015 manifesto, 18 self-professed eco-modernists wrote, “. . . we affirm one long-standing environmental ideal, that humanity must shrink its impacts on the environment to make more room for nature, while we reject another, that human societies must harmonize with nature to avoid economic and ecological collapse.” I firmly believe that second long-standing ideal, rejected by the eco-modernists, is cast aside at our enormous collective peril.

Nevertheless, without acceding to the overarching eco-modernist views of Lynas, Nordhaus, Schellenberger, and Marris, who care little about preserving whatever bits of pristine wilderness are left, I have to agree that the case for helping forests migrate is persuasive. And it appears that many if not most conservationists are coming to the same conclusion. Indeed, the pushback from traditional conservationists is subsiding as the grim reality of climate change asserts itself. The debate about assisted migration of species seems to have peaked in the years 2006-2014 (an article in Orion in 2008 summarized the arguments well). Today, assisted migration is widely discussed in forest conservation plans as a key component of “climate adaptation.” Public and private forestry professionals routinely forecast how the ranges of native tree species will shift, and plan accordingly. Assisted migration efforts are well underway in the forests of Alaska and western Canada. (Here is Connie Barlow’s information page on the subject, where you can find just about any imaginable resource.)

Reading the arguments as they evolved among conservationists over the past decade or two is sobering, frightening, and occasionally heart-rending. One realizes just how much is at stake, how much has already been lost, how much is at risk over the short term, and how much more over the long term. The essential motive of wild lands conservation was and is to keep relatively undisturbed areas away from human interference so that native species can persist in their myriad diversity, and so that evolution can continue to do its slow, transformative work. The fact that many conservationists are now contemplating or actively involved in assisted migration programs should tell us just how dire the climate crisis is.

The impact of climate change on forests is already staggering. Forest fires, pests, disease, and drought connected in some way with greater weather extremes and shifting rainfall and temperature patterns are decimating forests in North America, South America, Siberia, and Australia. And those impacts are projected to intensify dramatically in the next decades. Here is the EPA page on climate change impacts on forests (read it while it’s still there!).

Tens of thousands of people work in conservation in the U.S. alone—from employees of the Department of Interior to regional and local conservation officials and employees, to conservation biologists employed by industry. Their various philosophical and practical approaches have been subsumed under rubrics such as reservation ecology, restoration ecology, resilience ecology, and reconciliation ecology. Just about everyone agrees that the challenges are growing rapidly, and that one of the worst of these is the ethical dilemma of whether, when, and how to interfere with nature in order to mitigate the effects of past human interference.

E.O. Wilson has proposed the sensible strategy of setting aside half of Earth for the maintenance of biodiversity. Given large areas in which to maintain sufficient population sizes, and corridors for migration, it is likely that many species would be able to respond to a changing climate through adaptation, competition, and migration. But even Wilson’s “Half Earth” solution, bold as it is, might fail to save most of the planet’s forests. And without forests, innumerable other species would perish as well. The only way to save the forests now is to intervene, despite all the myriad risks that human intervention entails.

It seems almost silly to be discussing Wilson’s brave proposal in the context of new Trumpian political realities. The EPA will soon be a shadow of its former self, discussion of climate change will have been expunged from government web pages, and federal conservation work will be at least partly defunded, with whole programs disappearing. That means if assisted migration is to occur in the United States, it will depend largely on the action of private forestry companies and scientist-led citizen groups—backyard gardeners, state-supported botanical gardens, urban tree planters, and guerilla tree planting operations.

In a short 2004 video, Connie Barlow explains the rationale for helping an endangered conifer tree, Florida Torreya (Torreya taxifolia) recover from otherwise certain extinction. Connie coordinated the formation of Torreya Guardians, an organization that has legally planted nursery-grown seedlings of Torreya taxifolia in two forested plots of private land in the mountains of North Carolina. This is, of course, only a token example of the efforts that would be required in order to make a significant difference in the survival of North American tree species.

In addition to movements of resistance (against oil pipelines, among other things), there is also increasing need for citizen movements of preservation and conservation. A century from now, looking backward, which will have had greatest positive impact? Your guess is as good as mine.