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ShareMar. 4, 2008 — Widespread damage to plants from a sudden freeze that occurred across the Eastern United States from 5 April to 9 April 2007 was made worse because it had been preceded by two weeks of unusual warmth, according to an analysis published in the March 2008 issue of BioScience. The authors of the report, Lianhong Gu and his colleagues at the Oak Ridge National Laboratory and collaborators at NASA, the University of Missouri, and the National Oceanic and Atmospheric Administration, found that the freeze killed new leaves, shoots, flowers, and fruit of natural vegetation, caused crown dieback of trees, and led to severe damage to crops in an area encompassing Nebraska, Maryland, South Carolina, and Texas. Subsequent drought limited regrowth.
Rising levels of atmospheric carbon dioxide are believed to reduce the ability of some plants to withstand freezing, and the authors of the BioScience study suggest that global warming could lead to more freeze and thaw fluctuations in future winters. This pattern is potentially dangerous for plants because many species must acclimate to cold over a sustained period. Acclimation enables them to better withstand freezes, but unusual warmth early in the year prevents the process. A cold spring in 1996, in contrast to the 2007 event, caused little enduring damage because it was not preceded by unusual warmth.
The 2007 freeze is likely to have lasting effects on carbon balance in the region. Plants cannot resorb nutrients from dead tissue that would normally be remobilized within the plants during autumnal senescence, so many nutrients became less available for plants in 2008. Wildlife is expected to have suffered harm from lack of food, and changes to plant architecture could have long-term implications.
Gu and his colleagues propose that the 2007 spring freeze should not be viewed as an isolated event, but as a realistic climate-change scenario. Further study of its long-term consequences could help refine scenarios for ecosystem changes as carbon dioxide levels increase and the climate warms.
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 poplar trees were "surprisingly" slow to put out flushes of new leaves, and white oaks were particularly hard hit with freeze damage to both new leaves and flowers. On the other hand, trees located along shorelines--where the water stores heat--and underneath dense canopies seemed to be protected from the cold.
Compounding the stress on plants, as noted in the International Panel on Climate Change's fourth assessment report, is the prospect of prolonged droughts, which also occurred in the region last summer.
Reference: The 2007 Eastern US Spring Freeze: Increased Cold Damage in a Warming World. Lianhong Gu, Paul J. Hanson, W. Mac Post, Dale P. Kaiser, Bai Yang, Ramakrishna Nemani, Stephen G. Pallardy, and Tilden Meyers
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The above story is reprinted from materials provided by American Institute of Biological Sciences.
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