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Helping Trees Walk: Is Assisted Migration a Climate Solution or an Ecological Disaster?

Updated: Mar 1

“...Conservation is not just altruistic. It’s also selfish” (Tim McDonnell, New York Times). The impact of climate change on nature is concerning not only because of our empathy for the more-than-human flora and fauna that share our planet, but because our lives are also dependent on the health of our ecosystem. This is why conservation is becoming increasingly essential – and why scientists are turning to ever-stranger tactics to save the earth’s wildlife. They’re altering species’ DNA, spying on them with robots, and “helping trees walk,” assisting plants and animals in migrating hundreds of miles from their native territory. 


Climate change is affecting plants and animals’ habitat ranges, contracting them and shifting viable habitats from south to north, for instance, or higher in elevation. Organisms can adapt on their own – they’ve been doing it since the beginning of life on Earth. But most cannot keep up with the speed of human-caused climate change. Many trees, for example, can migrate only about 100 to 500 meters per year (for clarity, “migrate” refers not to an individual organism but the entire population.) That’s only a few football fields. And because of climate change, an estimated 12,000 species are at risk of extinction. The giant sequoia, for one, could be gone by the year 2100: in fact, a multi-millenium-old giant sequoia tree called the Waterfall Tree – one of the largest trees of its kind – died due to wildfire in 2020. 


That’s where assisted migration comes in. Assisted migration is the idea of helping move populations of plants or animals to new, more suitable habitats based on climate predictions in order to save them from extinction. Assisted migration does not involve uprooting the current population to transfer to a different home – instead, it’s about introducing new individuals to a more suitable location. For trees, that means planting seeds elsewhere. 


There are important distinctions to make between the different types – there’s assisted population migration, defined as “moving seeds to new locations within species range,” assisted range expansion, relocating to just outside of their normal range, and finally assisted species migration, moving them far beyond their current range. 


The lower risk associated with assisted population migration makes it the only form of assisted migration currently practiced by the U.S. Forest Service. There are many other local or independent organizations also testing assisted migration. These include the citizen-led PropagationNation, which works with, among other species, redwoods and sequoias; and the City of Portland’s Urban Forestry program, which is experimenting with 11 species, including the California black oak, canyon live oak, and the interior live oak. 

So far, there are good signs. Seeds such as the whitebark pine have been shown to grow  500 miles beyond their present range. Additionally, even a small amount of assisted migration can have great benefits: the new genes introduced to a population improve diversity in the gene pool, which can better a species’ chances of adapting to climate change independently. 




But there are many risks, too. The first and most obvious is that the species might simply not survive outside of the area where it currently dwells. Some species, such as the Florida Key deer, are what’s known as “narrow endemics” and only reside in particular places. The Key deer, true to their name, have only ever existed on a small island in the Florida Keys. 


The transplanted species could also become invasive. For example, scientists moved the rosy wolfsnail to Hawaii to consume African land snails, which backfired when it instead caused one third of native snail species to go extinct. Another risk is that the migrated species might hybridize with other, similar species – thus causing the original species to merge with a different population and disappear. 


Also, there is the fact that climate change is simply very difficult to predict. Shifting rates and effects of climate change could mean that a move to a new area might end up not being suitable for the species after all, decades or centuries into the future. 


To me, conservation always seemed laborious and painstaking, and for little payoff. But as Patrick Donnely, Great Basin program director with the Center for Biological Diversity, said, “moving them as opposed to just watching them go extinct seems to be the least bad option.” Of course, assisted migration comes with many risks, and it would be preferable if we prevented the damage from happening in the first place. But it only makes sense that in a human-caused climate crisis, something that is by no means “natural,” we should do all we can to find solutions, even if that means resorting to arguably unnatural interventions. 


If saving wildlife from extinction means moving the Florida Key deer out of the Florida Keys, or the California black oak out of California, then so be it.


 

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