The Santa Rita Experimental Range's 50,000 acres south of Tucson have served as an important outdoor laboratory for more than a century for researchers investigating sustainable grazing practices.
Prior to the station becoming a research facility in 1902, 2,500 to 3,000 cattle regularly grazed the site, said Mitch McClaran, director for research at the range and University of Arizona College of Agriculture and Life Sciences professor of range management.
"It was very overgrazed," McClaran said.
Researchers believed the site could accommodate 1,200 cattle, but that was deemed excessive for sustainable grazing in the in the 1950s, he said.
As studies continued and historic data was collected, the number had to be reduced.
Currently 600 to 700 head graze the Santa Rita Experimental Range, or SRER, under controlled conditions. The site is broken into numerous pastures through which the hungry cattle are rotated. This arrangement is sustainable because changes in livestock numbers and duration in pastures are adjusted on a monthly basis to conform to availability of forage vegetation under an approach called adaptive management, McClaran said.
The range, which butts up against the Santa Rita mountain range about 30 miles south of Tucson, receives from less than 11 inches of annual rainfall at lower elevations to up to 18 inches at higher elevations, mostly during a brief summer season when most vegetation growth occurs. Careful grazing practices have been developed to protect the ground cover.
When the summer rains begin in late June or early July, the cattle are allowed to graze for only 10 days in a site before moving on. This prevents the cattle from grazing plants a second time during the short summer growing season, otherwise the vigor of those plants would decline, he said.
And since grass and plant growth takes place only during the short rainy period, cattle grazing during the dormant season is also carefully managed, he said.
Cattle are closely monitored and allowed to consume 40 percent of the summer grass at a pasture before they are moved to another site. The remaining 60 percent of the summer growth is left intact, with grasses and plants protecting soil from erosion as well as providing food for wildlife, he said.
In addition to grazing research, the SRER plays a role in helping scientists understand climate change. The site has been chose as one of 20 National Ecological Observatory Network research sites that will use regional data to offer a global perspective on climate change issues. The NEON project, funded by the National Science Foundation, is slated to be up and running at SRER in three years, he said.
The project will study how vegetation and greenhouse gas exchange relate to climate changes over a 30-year period.
SRER's longstanding research base includes an archive of repeat photography images taken beginning from 1902 to the present. Using images taken over three- or five-year spans at 83 sites throughout the range, researchers get a long-term perspective on vegetation changes.
Photos from the early 1900s were taken using large-format cameras toted across the site on buggies, he said.
Such an historic image database lets researchers determine if conditions during a specific time period are unique, or have occurred before, he said.
Information collected over the years at the range is available to the public via the Internet, McClaran said. This includes the repeat photography archive and lots of other data
"This brings the Santa Rita Experimental Range to the globe," he said. "Users around the world can access information."
The range is home to 20 to 30 research projects at any time, McClaran said, with 100 scientists working throughout the site. Field studies typically take two to three years, he said.
The range was established as a U.S. Department of Agriculture site in 1902, administered by the U.S. Forest Service with heavy research involvement from University of Arizona scientists. In 1988 title for the site was transferred from federal to state hands and the University of Arizona College of Agriculture and Life Sciences took over management responsibilities, he said.