Assisted migration could help plants find a new home
Laura Nielsen for Frontier Scientists –
Plants, evolved to move with the natural rhythms of the world, cannot keep up with the rapid pace of climate change we are facing today. Their ideal habitats are sliding north as the world heats up. Do we get our hands dirty and help move the species most at risk, throwing the idea of conservation as preserving untouched land out the window? Or do we watch many plants go extinct before our eyes? It’s a harder question to answer than you might think.
Forecasts of the future
Average global temperatures are expected to increase by 2.2 to 10°F [1.4° and 5.8°C] over the next century, with higher temperature increases at higher latitudes. Even a modest estimate of 3.6°F [2°C] would shift ideal growing conditions for many plants in North America north by 200 miles [322 kilometers]. That would mean that a pine tree species would have to migrate an average of 2 miles [3.2 kilometers] per year- that is, pinecones would have to fall, (hopefully) be carried by animals, and sprout young pines further north which successfully grew to maturity and produced their own pinecones. Yet Kayri Havens, Chicago Botanic Garden’s director of plant science and conservation, notes that for most plant species, “Seeds only disperse a few hundred yards, half a mile at most, naturally.”
A biome is a community of plant and animal life. Many communities need to shift north. Ecosystems thrive in the climate that best suits them. And they are already on the move: North American plants are pushing the limits of their ranges either northward across latitudes or (where available) upward into the mountains, toward cooler temperatures. The question is how swiftly they can accomplish this shift. Many species cannot seed-disperse north fast enough to keep up with the climate they can tolerate, meaning their ranges are shrinking. We can already see the results in Arctic plants and animals that have nowhere to retreat to. The New York Times reports that an international team of scientists estimated global warming would drive 15 to 37 percent of species extinct by 2050. An even greater percentage will be put in danger of extinction because their habitats are changing so rapidly.
Not only are humans changing the world’s climate at a rapid rate never before witnessed via anthropogenic (human-caused) inputs like carbon dioxide, but we’ve made plants face a veritable obstacle course. Urban centers, agriculture, deforested areas, cattle ranges, and even interstate highways can prove impassable. And climate-tied stressors including record breaking drought, strange weather patterns, and unprecedented wildfire make it difficult for plant species to disperse and establish themselves. Journalist Michelle Nijhuis explains the related uncertainty succinctly: “Each species [is] reacting somewhat differently. Ecological communities, never as stable as we might like to think, are disarticulating in new ways.”
Margaret Davis, ecologist at the University of Minnesota, told NASA “Our best shot at preserving biodiversity may be to create large forest reserves at all latitudes,” which are linked by corridors to ease migration. And in last week’s feature, FrontierScientists took a look at seed banks and projects like the Bureau of Land Management’s Seeds of Success. 2011-2020 has even been declared the United Nations Decade on Biodiversity Yet despite the best intentions of these programs, for many species it will not be enough. To safeguard biodiversity we might want to pursue even more drastic efforts. The famous conservationist Aldo Leopold wrote in his journals: “...Who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering.”
Conventional strategies aren’t the only option in our fight to save endangered species. Lately there has been discussion among botanists and conservationists surrounding a controversial approach: assisted migration. Assisted migration proponents propose that humans ship plant populations northward, planting seeds or re-planting established adult specimens in areas where conditions and temperatures are right for them to thrive. Essentially, the approach would mimick what plants would do themselves over time, but speed up the dispersal process with human help.
After all, humanity’s neverending need for progress and machinery has caused this problem. Can humanity not help to mitigate the ills that result?
There are risks
Yet it’s a controversial proposal, and one being discussed with caution. Opponents of assisted migration worry that choosing what plants to move would be difficult, the process potentially costly. Transplanting a species to another habitat is always risky because the species might outperform the plants that were already there, taking up resources and upsetting the local balance. We’ve introduced invasive species before with ill results: kudzu, leafy spurge, garlic mustard, creeping thistle. Others warn that artificially-relocated plants could potentially carry diseases that their local habitat was able to resist but that their new neighbors might succumb to. Unexpected interbreeding between species could result in hybrids, lowering overall genetic diversity. And, importantly, laws generally forbid moving flora from one place to another. These apply especially to endangered species if the destination is not part of their original range. To some, the act seems too much like playing God.
There are payoffs
To others, we’ve already enforced such radical changes upon our planet that it would seem irresponsible to not try to mitigate them. And, they point out, species are already moving to ranges where we haven’t seen them before. For many plants the move won’t be fast enough. Efforts like assisted migration could reduce the number of species that face certain extinction as the planet warms.
The perhaps more cautions supporters of assisted migration have proposed using botanical gardens as stopovers for plants, because botanical gardens have the resources, expertise, and connections to watch how plant species interact with one another and notice the characteristics of possible invaders. Some experts note that species migration is normal: the last ice age pushed North American plants south toward warmer refuges, and then many plant species followed the retreating ice edge north again. The difference is merely that the ice ages occurred over the span of many thousands of years, while our modern-day climate shift is happening right before our eyes.
In our lifetimes, we will witness many iterations of a new world. What will be growing there?
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- ‘Assisted Colonization and Rapid Climate Change’ O. Hoegh-Guldberg et.al. in Science Magazine (2008) via National Wildlife Federation
- ‘A Hunt for Seeds to Save Species, Perhaps by Helping Them Move’ Anne Raver in New York Times : Science (2009)
- 'The Migrating Boreal Forest' Rebecca Lindsy for NASA Earth Observatory (2002)
- ‘Plan seeks 'chaperones' for threatened species’ Virginia Gewin in Nature | News (2013)
- ‘A Radical Step to Preserve a Species: Assisted Migration’ Carl Zimmer in New York Times : Science (2007)
- ‘Taking Wildness in Hand: Rescuing Species’ Michelle Nijhuis in Orion Magazine (2008)