Oct. 17, 2000 COLLEGE PARK, Md. - An off-season "Jack Frost" is nipping life away from some plants in many regions of the country according to a recent University of Maryland paper featured in this month's issue of Ecology Letters.
David Inouye, Maryland's professor of biology, has found that global climate change influences early and late frost events, which inhibit growth and possibly damage many plants. Climate change has also impacted animal populations that depend on plants that suffered frost damage. Inouye, who has studied global climate change impact on animal and plant life for over 20 years, suggests there is great evolutionary significance of frost in context of global warming that warrants further research.
"Five to 15 percent of agricultural production is lost to frost each year worldwide. Frost determines the growing range for many species of garden and agricultural plants, so changes in the distribution of frost in the future may influence where certain plants can be grown," said Inouye.
Subfreezing temperatures that signal frost conditions can cause formation of ice crystals within or between the plant cells, which lead to physical damage and trigger physiological problems. Crop plants are often impacted by this kind of cellular death when unusually low temperatures occur overnight, causing a significant ecological and economic effect on the crop plants.
This kind of "killing frost" has a strong impact during below-freezing temperatures, particularly at the beginning of the growing season, when plants have lost the physiological protection against freezing that protects them. The damage can be specific to certain life stages: buds and new leaves of woody plants are more susceptible than older tissues (e.g. stems, mature leaves). At a high-altitude field site in Colorado, Inouye found flowers and ovaries are often killed when older leaves are not affected by frost.
He says it may appear practical to protect some fruit trees or other crops from frost by methods such as spraying water or using heaters or fans to move cold air away, but wildflowers don't reap benefits from this kind of protection.
Inouye adds, "The degree to which plants will suffer from frost damage in the future will depend on the interactions between temperature and precipitation, both of which are predicted to change. According to some models, alder, birch and poplar trees will be affected and these early-flowering trees will suffer greater frost damage in the future."
Frost can also cause a loss of food supplies for an animal species, either through killing the leaves or through loss of seeds or fruits. During a previous study cited by Inouye, it was found that the year following a frost event a population of squirrels, who consumed acorns of several different species of oak trees, dropped 17 percent. However, the year of the frost was the largest squirrel population recorded in five years.
Since the study only reported data for one year following the frost, Inouye believes it would have taken a few years for squirrel populations to recover fully. To understand further frost impact on animal species, he suggests a long-term database of population numbers, data on diet, and availability of food items in the diet to examine the population before, during and after a frost event.
Global climate change may continue to influence the frequency and distributions of frost events. Inouye notes few studies address how climate change might influence late spring frosts. If global warming results in earlier flowering in temperate species, flowers might become more susceptible to frost damage. He suggests further research on how the influence of global climate change on frost events may have a widespread impact on plant and animal life.
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