Last week at the annual UConn Garden Conference there was a most diverse series of presenters. All had valuable insights into varied horticultural topics but I found the last talk most intriguing and thought provoking. It was by Dr. Jesse Bellemare of Smith College in Northampton, MA and his topic was Horticultural Insights into Plant Conservation and Climate Change.
Long time gardeners are well aware that changes are taking place in their yards and gardens due to the overall warming of the earth’s atmosphere because of the burning of fossil fuels. Plants are leafing out 2 to 3 weeks earlier, dandelions and forsythia are blooming in January, earthworm activity was noticed in my yard this February, tomatoes were still being picked the first week of November, exotic insect pests like the cross-striped caterpillar are moving in. I’ve been gardening for over half a century and when the changes I see are magnified over large food production areas in the U.S. and combined with prolonged droughts and greater numbers of extreme storm events, I can’t help but feel this does not bode well for our farmers or our food supply – but that may be a topic for another time.
Dr. Bellemare addressed the topic of managed relocation. Up until now, in order to preserve species, whether they be plants or animals, the present thought was to spread the news about how devastating manmade climate change will be and to try to convince decision makers to take steps to limit carbon emissions and also do our best to protect rare or endangered or other species with limited dispersal abilities. To my knowledge, this is not really working. So should we plant conservationists, researchers, plant lovers and gardeners just let some species become extinct?
I don’t think so and neither does Dr. Bellemare. He has been collecting data which has led to some surprising, yet not really unanticipated conclusions, and I would like to share them with you.
In his presentation he covered some information about species native habitats and how they disperse. Keep in mind that the three greatest threats to a species are habitat destruction, replacement by invasive species and climate change. According to Dr. Bellemare, anywhere from hundreds of thousands to more than a million species may become extinct due to climate change. Not only may these species be important from a biodiversity standpoint but what may they offer in terms of medicinal properties? We may never know.
A new conservation strategy proposed by Dr. Bellemare would be one of assisted migration or managed relocation. Basically this involves moving a threatened species into a new (usually more northern) region where it would be predicted to survive and reproduce. Critics worry about the invasiveness as well as less attention focused on native habitat protection. There is presently a heated, ongoing debate surrounding the Florida torreya, an endangered native conifer. The question is whether, as its native habitats are in decline, should this species just be allowed to die out or since it does well in more northern climates should it be transplanted and encouraged to reproduce?
Plant species that would be candidates for managed relocation tend to have a relatively small range usually in the southeastern part of the U.S. that was not affected by the last glacial period. They also have a rather limited seed dispersal ability and may be subjected to rapid climate change. These plants would not have time to naturally evolve so it falls on us humans to decide their fate.
A lot of these plant species are already being grown by gardeners, botanic gardens, college arboretums and other plant collectors. And I might add, successfully, despite their more southern origins. Many of these species have occurred as individuals in plant collections, arboretums and on college campuses. Some challenge their invasiveness potential but realistically most of the invasive species found in the northeast are from other countries and not southern parts of our own country. Plants prone to widespread distribution have pretty much already distributed their progeny over the past thousand years or so.
Also remember that the glacier that came down from Canada about 15,000 years ago wiped our most of our native New England flora and most of our present day flora migrated up from the south. So many of our plants already share a common biological and biogeographical history. According to Dr. Bellemare, this may lessen the threat of “unexpected and negative ecological interactions.”
A most interesting case involving climate change and the ability of a small-ranged plant species to naturalize in New England is the saga of the umbrella magnolia (M. tripetetala).
Dr. Bellemare and his lab at Smith College in Northampton, MA have been documenting both the locations of previously planted umbrella magnolias as well as their reproductive ability and success in as many locations as they could over the past few years. This species is native to southeastern United States and inland as far as Arkansas and Oklahoma. For the past 100 years or so, specimens have been planted in arboretums, college campuses, public gardens, and in private collections. Recent field studies by Dr. Bellemare’s lab have found naturalized populations in several Massachusetts sites. These sites have not just included individual trees that may have been planted 50 to 100 years ago but younger plants that have originated over the past 20 to 30 years.
What should we make of this? For one, it seems that the umbrella magnolia is able to reproduce under a wide variety of forest canopy scenarios – from wet, swamp maple habitats to shady conifers to more open revegetated pine forests. This may suggest that M. tripetala is able to naturalize across a broad range of habitats and environmental settings.
It is what is known as an adventive species – not native or fully established in a new habitat but may be locally or temporarily naturalized.
Although the umbrella magnolia is naturalized in many areas in southeast United States and westward through regions of Arkansas and Oklahoma, its natural expansion is limited but horticulturists have planted this species in many New England states over the past 100 years of so.
Most of these were individual specimens in arboretums, on college campuses, in public gardens or just on individual estates. Many survived and during the past 20 to 30 years it was discovered that they spawned reproducing populations of seedlings and young trees. When Dr. Bellemare looked at core samples, he concluded that reproduction of this species likely began in the last 20 to 30 years. Remember some of the original trees were planted over 100 years ago. What caused them to start reproducing?
The most likely hypothesis, espoused by Dr. Bellemare and like-minded colleagues, is that changes to our climate have allowed plants to produce seed and for favorable conditions for seed germination from these otherwise long-established horticultural specimens. Other researchers have found similar trends for other magnolia species on Long Island.
Given this information, what should we as gardeners do? I for one will be ordering more plants that are native to the east coast but maybe listed as marginally hardy to New England. One never knows whether their small purchases may add up to a big win for plant conservation.