Warming Climate Could Mean Trouble For Farmers And Horticulturists
October 3, 2013

Climate Change Could Render Traditional Planting Methods Unreliable

redOrbit Staff & Wire Reports - Your Universe Online

The degree-day model used by farmers and horticulturists to determine when it is safe to plant crops and ornamental plants could become untrustworthy as a result of global warming, according to research now appearing online in the journal Global Change Biology.

The degree-day model, which has historically helped agricultural workers determine when leaves will arrive, is a measure of how many degrees above or below a mean the temperature has been over a period of time. The model makes sense when the climate is not changing, but the study authors report their research shows the method could become unreliable as temperatures begin departing from their historical norms.

James Clark, a Duke University environment and biology professor, and colleagues from Marine Biological Lab at Woods Hole and the University of Georgia are working on a statistical model that attempts to look at the climate in the way that plants see it. As part of their research, Clark’s team collected data from the Duke Forest in North Carolina and the Harvard Forest in Massachusetts.

“The timing of the first leaves on trees and plants can make or break an agricultural season. Too early, and the leaves might be blasted by the last frost. Too late and they miss out on maximizing the growing season,” the university explained in a statement.

As global warming causes wintertime temperatures to rise, plants could be more vulnerable to poor timing, Clark and his colleagues discovered. One of their findings is that warming has the most impact in the period from mid-February through mid-March – just a handful of few weeks before the buds would be expected to open. Increasing temperatures during those weeks have a greater impact on the plant’s timing than any other time of the year.

In the forests where Clark and his associates did their work, there is a mix of native trees that live in open-topped, temperature-controlled chambers within natural forests. Some plots are unheated, while others were heated to three degrees Celsius or five degrees Celsius higher than the ambient temperature.

“In the case of the Duke plot, that meant that the +5C chamber experienced no below-freezing temperatures in the unusually mild winter of 2012,” the university said. “It was thought that the trees were ‘programmed to experience a certain amount of chilling and then warming,’ Clark said. But in this case, they wouldn't have met their usual requirement for chilling before experiencing the warming that signals it's time for spring.”

Nonetheless, the plants budded extremely early, leading the professor to surmise that the dormant season is “more complex than we thought.” Some types of crops and flowers are more sensitive to warmer-than-normal winters, and some will advance their budding to match the earlier season while others are unable to, Clark explained.

“As the climate changes, can we see differences in how species track change through time? Averages don't work anymore because the plants aren't seeing the average,” he added. His team’s research, as well as the he heated forest experiments, was funded by the US Department of Energy.