FORT COLLINS-A long-term study by Colorado State University ecologists suggests that warmer nights are producing a lengthened growing season and changes in prairie vegetation on the shortgrass steppe of eastern Colorado and surrounding states.

Working at Colorado State's Shortgrass Steppe Long-Term Ecological Research (LTER) station, the ecologists drew on 23 years of climate and vegetation data that suggest a warming trend that could lead to longer growing seasons. Those longer seasons, in turn, seem to favor cool-season grasses and weeds over native warm season plants like blue grama grass. The team's findings appear in the current (Jan. 8) issue of the journal Science.

Colorado State doctoral student Richard Alward; James Detling, professor of biology; and Daniel Milchunas, research scientist in the university's Natural Resource Ecology Laboratory and rangeland ecosystems science department, looked at how warmer nights appear to have contributed to a decrease in blue grama, a hardy forage plant favored by livestock and grazing wildlife.

While temperature data are localized, they support global climate change studies that suggest an overall warming. A key factor is an increase in nighttime cloud cover that traps heat near the earth's surface, Alward said.

"Blue grama is a grass that is very drought resistant and grazing tolerant, and under normal conditions it'll hang in there," Detling said. "It's very sensitive to water and is more productive under moist than under dry conditions. But the results of our study indicate it may be sensitive to temperature as well, particularly minimum temperature."

That minimum temperature also is known as the nighttime low temperature. The trio found that average annual minimum temperatures are increasing at about twice the rate of average annual maximum temperatures (the daytime highs) at the Shortgrass Steppe LTER site. In terms of the growing season, that
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Contact: David Weymiller
dweymiller@vines.colostate.edu
970-491-6851
Colorado State University
8-Jan-1999