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Climate change on the Great Plains.

Many scientists and environmentalists expect the level of carbon dioxide ([CO.sub.2]) in the atmosphere to double during the next 50 years. However, they don't know how extra [CO.sub.2] will alter global temperatures and precipitation, or which geographic areas will be most affected.

To answer these questions, ARS scientists are using complex computer models to project the many environmental interactions that determine how specific sites might respond to different climate-change scenarios.

Interpretation of these projections should allow time for farmers and ranchers in affected areas to adapt.

"For example, if climatic changes become unfavorable for livestock production in some areas of the Great Plains, ranchers can adjust the number of animals on their ranches, the time of grazing, and even the type and genetic composition of the grazing animals," says Agricultural Research Service range scientist Jon D. Hanson. "The more we know in advance about climate changes, the more we can do to prepare for them. This is especially true if we want to breed livestock or grasses with genetic traits better suited for the new environments."

In preparing for that change, Hanson and ARS ecologist Barry B. Baker are using computer models to simulate the results of various climatic shifts and the effect of these shifts on beef cattle production.

They used SPUR (Simulation of Production and Utilization of Rangeland) and CBCPM (Colorado Beef Cattle Production Model) to simulate two 30-year scenarios of how range grass and beef production would be transformed under increased [CO.sub.2] concentrations and resulting changes in climate, such as higher temperatures and increased precipitation.

SPUR simulates the response of grasses and shrubs growing in various soils. CBCPM is a cow/calf life cycle model that simulates individual animal response to changes in forage quality and quantity, as well as to changes in weather conditions. SPUR was developed by ARS, CBCPM by Colorado State University.

Scientists obtained weather data for their computer simulations by combining historical weather data from 24 weather stations, from Montana to Texas, with weather predictions from the Goddard Institute for Space Studies' General Circulation Model. The circulation model simulates potential changes in climate when concentrations Of [CO.sub.2] change.

"For ranchers, the bottom line is how much beef they can produce on their ranches, either to sell or to keep as replacement stock. The range model, the beef model, and the circulation model - working together - predicted that some ranchers will benefit, and others will not, from the increased [CO.sub.2]," says Baker, who coupled the SPUR and CBCPM models to produce this information at the Great Plains System Research Unit, Fort Collins, Colorado.

At one simulation site near Rosebud in southeastern Montana, ranchers could expect about a 65-percent increase in forage production. Cows would use that extra forage to produce calves that weigh 6 percent more when weaned from their mothers.

On the other end of the scale, ranchers in the Texas Panhandle could expect calf weaning weights to decrease by 3 to 4 percent - despite a 9-to 12-percent increase in forage production. The researchers believe this is due to the higher summertime temperatures projected.

"Overall, effects of climate change simulated by the models were positive for sites in the Central and Northern Plains, while ranchers on the Southern Plains can expect beef production to suffer," says Baker. "However, this decrease may be overcome by using animals that are more heat tolerant."

"We chose three sites - one each in Texas, Nebraska, and Montana, - to illustrate differences from south to north. All sites experienced a temperature increase," says Hanson.

In Texas, precipitation was the same, but 11 percent more moisture evaporated from both plants and soil surfaces via evapotranspiration. Grass production increased by 18 percent, but cattle ate 22 percent less, mainly because the forage was less digestible and the cattle suffered some heat stress. This resulted in cows weighing 12 percent less and calves 5 percent less at time of weaning.

In Nebraska, precipitation rose by 7 percent and evapotranspiration by 32, producing 27 percent more grass. The higher temperatures negated most of the beneficial effects of having more grass, so cow weights decreased by 2 percent and calf weaning weights rose only 1 percent.

In Montana, the temperature increase was welcome. It extended the length of the frost-free growing season by several weeks. Precipitation also increased by 18 percent. The total effect was a 6-percent increase in forage production, 12-percent increase in digestibility, and more favorable weather for livestock. Cattle ate 34 percent more, leading to an increased cow weight of 8 percent and calf weaning weights of 19 percent.

"From the perspective of any individual rancher, climate change will probably be imperceptible from the yearly variations normally encountered. Any long-term change will be gradual enough to allow for management adjustments to cope with an altered environment. For example, ranchers might include more genetic material from the Bos indicus species, or Brahman-type cattle. These cattle have more heat tolerance than the B. taurus species, which includes breeds such as Hereford and Angus. Or, ranchers might seed new grasses to take advantage of the changing weather," says Baker.

The scientists coupled these simulations with a Geographic Information System that enabled them to produce maps indicating the relative importance of global change to rural communities.

Key to calculating the impact on these communities was a Range Dependency Index that combines data from agricultural and population censuses. The index linked the importance of rangeland production to overall rural incomes in counties from the Canadian border south to the Mexican border.
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Author:Senft, Dennis
Publication:Agricultural Research
Date:Feb 1, 1993
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