Killer freeze of '07 illustrates paradoxes of warmi...( OAK RIDGE Tenn. March 5 2008 -- A de...)

OAK RIDGE, Tenn., March 5, 2008 -- A destructive spring freeze that chilled the eastern United States almost a year ago illustrates the threat a warming climate poses to plants and crops, according to a paper just published in the journal BioScience. The study was led by a team from the Department of Energy's Oak Ridge National Laboratory.

The "Easter freeze" of April 5-9, 2007, blew in on an ill wind. Plants had been sending out young and tender sprouts two to three weeks earlier than normal during an unusually warm March. Plant ecologists, as well as farmers and gardeners, took note of the particularly harsh turn of the weather in early April.

"The warm weather was as much a culprit for the damage as the cold," said lead author Lianhong Gu of ORNL's Environmental Sciences Division.

"We see the paradox in that mild winters and warm, early springs make the plants particularly vulnerable to late-season frosts," Gu said.

Gu's team observed satellite images and field data to establish the extent of the 2007 spring freeze. They also assessed the long-term and short-term effects on the terrestrial carbon cycle with respect to plant activity in normal years. Short-term effects were "profound," Gu said.

"In the period just after the freeze we saw a large reduction in the fraction of absorbed photosynthetically active radiation, which is a sensitive indicator of plant growth," he said. "We also noted that the regrowth in the following weeks and months did not result in the levels of plant development in previous years."

Gu's team hypothesized that the freeze could have long-term effects on forest carbon uptake because of damage the cold did to the prematurely developed plant tissues, which could affect future growing seasons. The associated carbon and nutrient losses may affect growth in future years.

Beyond devastated horticultural crops, the study noted that some species suffered more than others. Yellow
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