Assisted Migration of Native Plants


A couple of weeks ago, I attended a very interesting symposium, “Rooted in Place,” sponsored by the Berkshire Botanical Garden.  The focus of the symposium was new trends in environmentally-based gardening, and it led off with a talk by the marvelous Dr. Douglas Tallamy about fostering moths, butterflies, and caterpillars to feed bird populations.  I had heard him speak before, but this talk contained fresh information from his new book (to be published in February, 2020), Nature’s Best Hope.  The talk I found most interesting on this occasion, however, was delivered by Dr. Bethany Bradley, an ecologist at the University of Massachusetts Amherst.

Dr. Bradley spoke to the subject of assisted migration.  She began with a stunning fact, that if we continue on the path we are on now, the climate of Massachusetts will be by mid-century (in just 30 years) similar to that of present-day Maryland.  Then she shared a possible response, that of assisting the migration of warm-climate species to central New England.

She noted some possible complications.  There is, for example, the danger of introducing invasive species, even when the introductions are limited to North American natives.  She cited the black locust (Robinia pseudoacacia), a native of the central to southern Appalachians that has been introduced to central New England and become invasive there.  Then she discussed how ecologists might predict the behavior of natives released onto new, more northern territory, while admitting that such science is not foolproof.

Black locust, Robinia pseudoacacia, by By AnRo0002 – Own work, CC0,

This is one reason, she stated, why some ecologists resist assisted migration altogether, asserting that it is safer not to do anything than to risk doing something harmful.  But given the holes that climate change is going to tear in our local ecosystems, Dr. Bradley said that she thought that doing nothing would in fact be harmful in itself.  If we leave such holes unfilled, she pointed out, something is going to move in to fill them, and it will likely be garden escapes, invasive exotics.

As Dr. Bradley pointed out, gardeners are already involved in assisted migrations on a grand scale, by their purchasing and planting of non-local plants.  She wants to harness that for good, by persuading gardeners to experiment with warmer-climate natives, rather than the exotic species we so often favor.  Gardeners can have a powerful impact if they insist that local nurseries and garden centers stock such natives.

There is a lot to think about, pro and con, with respect to this subject.  If you would like to hear it discussed at greater length, you may wish to listen to my interview with Dr. Bradley on my podcast, “Growing Greener.”

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Thomas Christopher

My father was a compulsive tree planter, but it was my mother who taught me the finer points of gardening.

Her homeschooling was followed by two years in the New York Botanical Garden’s School of Professional Horticulture, and then ten years as horticulturist at an Olmsted Brothers designed estate on the Hudson River Palisades.

I’ve worked as a horticultural journalist for 35 years, contributing to publications ranging from Martha Stewart Living to the Journal of the Royal Horticultural Society and The New York Times.  My most recent book is Nature Into Art: The Gardens of Wave Hill, which is a tour of the lessons to be learned from that great public garden.  I’m currently focusing on my new podcast (at which features weekly interviews with leaders of environmentally-informed gardening.

My special enthusiasms include sustainable gardening, especially sustainable lawns;  heirloom chicken breeds; and recreating vintage New England hard ciders.


Contact Tom by email


  1. Whether or not this is a good idea remains to be seen. However, if one decides to do this, then there’s the problem of timing. I’m in zone 8a. Exactly when will I become zone 9 and when I am, could the cold temps suddenly swing back to zone 8a for a day or two? I know there are many gardeners who play with plants that don’t grow in their zone, but I’m not willing to chance it. While climate change doesn’t give a da*n about whether or not I like plants from hotter zones, the fact is that I don’t love cacti and agaves. I am, however, planting more plants that span zones 7-9, but will I eventually be a zone 10 and if so, does this mean those plants are toast? Perhaps by then, I’ll be compost, and it won’t matter. P.S. I’ve been listening to “Growing Greener”. It’s great.

  2. Thanks for the critique — you raise some important issues. Assisted migration is a provocative idea but I don’t think the ecologists have examined the subject in depth yet. I do know that my garden is half a USDA zone warmer than it was when I started planting 15 years ago. I’m experimenting with pawpaws, a native tree which wouldn’t have fruited successfully there a generation ago. And I’m hoping to experiment with native persimmons. A small start, but a beginning nevertheless.
    I’m glad you enjoy “Growing Greener.”

  3. We’ve had salvia ‘Black and Blue’ growing in our garden in the Columbia Basin for years. We were Zone 6B when we started this garden, but have recently been reclassified Zone 7A. Yet last February saw some evil cold days – down to 0°F or a bit below. Black and Blue is still with us, because it dies down to the roots in winter and we have it growing right against the house, south side, and semi-protected from the wind.

    Plants slightly out of our zone can be planted in protected mini-habitats, and over time we can experiment in moving offspring or cuttings into other areas of the garden.

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