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Early Spring Flowering Sets Record

CAS study: climate change speeding, but not preventing, blooms

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The truth is, April showers do not bring May flowers; long cold winters do, at least when it comes to some species that flourish in the New England woods. That’s what concerns conservation biologists like Richard Primack, who worries that the trend toward shorter and warmer winters could play havoc with mechanisms that tell plants when to bloom and could eventually forestall any bloom at all. In a new study, Primack, a College of Arts & Sciences professor of biology, and postdoctoral researcher Elizabeth Ellwood (GRS’12) demonstrate that while those flowers are blooming earlier than ever, at least they are still blooming.

“In 2010 and 2012, plants in Massachusetts flowered earlier than recorded in any year since 1852,” says Ellwood. “We have not found evidence that plants have reached a physiological threshold beyond which they cannot respond to warming temperatures.”

Primack and his team have been chronicling the dates that flowering plants bloom around Walden Pond for several years and comparing their observations with those made by Henry David Thoreau in the mid-19th century. His most recent research, done with Ellwood, Charles Davis at Harvard University, and Stanley Temple at the University of Wisconsin, also studied data collected since 1935 by Aldo Leopold in Sand County, Wis. That new study, published in the open-access journal PLOS ONE, shows that many plants—such as highbush blueberry and pink lady’s slipper orchid—flowered up to 4.1 days earlier for every degree Celsius rise in mean spring temperatures. It also showed that the historical patterns of early flowering in warm years and later in cold years can predict flowering times even in exceptionally warm years. And it found that wildflowers just keep flowering earlier as the climate warms.

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A warming planet will “reach a point at which the ecosystems are going to start to fail,” Primack says. Photo by Vernon Doucette

“In 2010, plants flowered three weeks earlier than in Thoreau’s time, and we thought we’d never see another year like that,” says Primack. “But then two years later we had another record early flowering year, both in Massachusetts and in Wisconsin.”

Still, Primack wonders how far nature can be pushed before there are no blooms at all. “These plants have shown remarkable resilience over decades of changing weather,” he says. “But it is unknown whether plant flowering times will continue on a linear trajectory of earlier flowering, or if at some point plants instead will be unable to keep pace with climate change.”

Ellwood points out that even if the flowers are still blooming, the timing of their blooms can have implications at the ecosystem level.

“Spring plant growth indicates the start of the growing season and will influence ecosystem processes such as nutrient cycling and carbon sequestration,” she says. “Interactions with animals will also be impacted as herbivores depend on spring plant growth and pollinators rely on open flowers. The timing of when plants and animals begin spring activity can be altered by temperature to varying degrees, and there is still much to understand about how temperature extremes will affect different organisms.”

In another project, Primack looked at how the warming trend alters the ability of trees and plants to absorb carbon dioxide from the atmosphere. The intuitive effect—trees would grow better as warmer temps stretch out the growing season, allowing them to vacuum more CO2 from the atmosphere—may not happen: a longer, warmer growing season could decay more material on the forest floor, which might, in turn, lead to more CO2 in the atmosphere, he says.

Left unchecked, Primack says, a warming planet will “reach a point at which the ecosystems are going to start to fail—there won’t be enough trees, there won’t be enough birds and insects in the systems. They’re not going to be absorbing enough carbon dioxide. They’re not going to be absorbing the waters to prevent flooding. They’re not going to be creating soil.”

2 Comments
Art Jahnke

Art Jahnke can be reached at jahnke@bu.edu.

2 Comments on Early Spring Flowering Sets Record

  • Bryan Hamlin on 01.25.2013 at 10:52 am

    Thank you for this excellent article on such an important, if troubling, subject.
    My colleagues and I found similar results in terms of earlier blooming times in our study of the flora of the Middlesex Fells. See Rhodora (2012) vol 114: 229-308, in particular pages 252-253.

  • Theresa Greger on 05.23.2013 at 8:59 pm

    I am not a scientist. But it appears that Primack is being very short sighted. Seeing everything from a human’s point of view, he says “the ecosystems are going to start to fail” which I believe is incorrect. The ecosystems we know will change to accommodate the climate, just as the plants we now know have evolved to fit climate of our century. That is success for the ecosystem. The Earth’s ecosystems will continue to evolve, adjusting to changes as they have since the earth was formed. We may not like the rate of change, but evolution continues.

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