From one end of the Americas to the other, climate heating is subjecting the plant world to radical change, with cold-resistant species increasingly yielding place to those that welcome the rising warmth.
That badge of Canadian identity, the sugar maple, may one day turn sour. As global temperatures, driven by profligate human use of fossil fuels, continue to soar, Acer saccharum could simply lose its habitat and no longer sweeten the forests from Novia Scotia to the Appalachians.
And the southern live oak, so associated with Florida that a city there preserves its name, may find life too hot for comfort: in the south of the state, Quercus virginiana could one day be replaced by trees from the Caribbean or even further south, such as the already present Cuban mahogany Swietenia mahogani or the Gumbo limbo Bursera simaruba.
And in what was once the reliably wintry city of New York, that marvel of old Mississippi the southern magnolia, Magnolia grandiflora, has begun to multiply and bloom ever earlier each year.
These species shifts are just part of a larger trend in the Americas, from Hudson Bay to Tierra del Fuego, according to new research in the journal Nature Climate Change.
“If we lose some plants, we may also lose the insects, birds and many other forms of wildlife that are critical to our ways of life”
Researchers analysed 60 million records of 17,000 plant species in almost 200 New World eco-regions, from 1970 to 2011, to identify a pattern of change in response to heat: a phenomenon called thermophilisation.
“Almost anywhere you go, the types of species that you encounter now are different than what you would have found in the same spot 40 years ago, and we believe that this pattern is the direct result of rising temperatures and climate change,” said Ken Feeley, a biologist at the University of Miami, who led the research.
The study – two continents, and a range of temperature regimes from near-Arctic to equatorial and onwards, almost to the edge of the Southern Ocean – confirms the big picture, but dozens of earlier studies had already built up a mosaic of observations that told much the same story.
As temperatures rise, and precipitation patterns shift, plants respond. The forests of the northern hemisphere everywhere are vulnerable to heat and drought, and even species considered resistant to drought could be about to succumb.
In the lowland tropics, researchers have warned that conditions could become so intemperate that some species may fail to germinate and renew their tenure in the forest. Researchers have observed tropical species moving uphill to find more equable temperature regimes, while others have warned that those upland species that are comfortable at height may soon find it so hot there could be nowhere left to go.
The latest study shows once again that, in any ecosystem, those species that are more likely to cope with colder temperatures are being replaced by others that just like it hot.
“Some of these changes can be so dramatic that we are shifting entire habitat types from forests to grasslands or vice versa – by looking at all types of plants over long periods of time and over huge areas, we were able to observe those changes,” said Professor Feeley.
“All animals – including humans – depend on the plants around them. If we lose some plants, we may also lose the insects, birds and many other forms of wildlife that we are used to seeing in our communities and that are critical to our ways of life.
“When people think of climate change, they need to realise that it’s not just about losing ice in Antarctica, or rising sea levels – climate change affects almost every natural system in every part of the planet.”
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