Lovegrass taking over

Refuge's burn policy can't kill it, UA study finds

Fifteen years of planned burning has failed to control an exotic grass that is pushing out native species in the Buenos Aires National Wildlife Refuge, recent University of Arizona research shows.

Still, refuge operators plan to continue the burning, in part because they don't know any other way to stop Lehmann lovegrass.

The grass, along with other non-native plant species, dominates many semi-desert ecosystems, reducing diverse native habitats to seas of uniformity.

When a non-native species controls a grassland, it can permeate the system on every level, taking over weaker native species and stunting the diversity of the area, said Guy McPherson, UA professor of renewable natural resources, who co-authored the study on the lovegrass.

The reduction of diverse plants in a habitat can alter all other life, which could mean a threat to animal species in the area, McPherson said. Part of the current research on Lehmann lovegrass seeks to determine how much the exotic plant impacts insect and animal species - early information suggests a threat, but such evidence is still weak.

"Loss of biological diversity is, I think, one of the greatest threats facing humanity," McPherson said. The refuge was created in 1985 to establish a breeding population of the masked bobwhite quail and to further restore the natural habitat of the area. Prescribed burns were initiated to reduce the growth of mesquite and Lehmann lovegrass, said Sally Gall, a wildlife biologist at the refuge.

The results of the UA data analysis, presented at the recent Ecological Society of America meeting by UA graduate student Erika Geiger and McPherson, show that fire hasn't reduced either one.

Gall said prescribed burning will continue at the 116,000-acre refuge south of Tucson in the hope that long-term benefits will accrue to the habitat.

The UA study is a valuable tool for evaluating management techniques, but more time and research are needed to tell whether fire is useful, she said.

Nearly 70 years ago, the U.S. Soil Conservation Service introduced the resilient South African grass to restore overgrazed grasslands and soil in the Southwest.

The introduction of Lehmann lovegrass followed a worldwide search and was considered a major victory for the region's agriculture.

"Seventy years ago, Lehmann lovegrass represented a significant accomplishment," said McPherson, who initiated the research in 1996 at the request of the refuge. "They spent millions of dollars finding it. How can we expect to get rid of it overnight?"

Lovegrass was considered a victory because it grows fast, matures fast, spreads a phenomenal amount of seed and survives drought better than native grasses, said Geiger, who is trying to find how varying nitrogen levels in soil can restore native plants.

The implications were greater than most anticipated at the time, Geiger said.

Prescribed burning became a popular tool for land managers, because it is inexpensive, natural and would presumably restore soil and plant life.

But Geiger and McPherson's research showed that lovegrass population springs up too quickly for fire to have a lasting effect.

If nothing else, the study suggests that land managers should be aware that controlling a plant system is much more complicated than simply lighting fires, McPherson said.

Now that burning seems to be an ineffective tool in reducing the plant, he and other UA researchers are trying to pinpoint how large a threat the grass is and to find what, if any, recourse is available to control the exotic species.

Wildlife and fisheries professor Bob Steidl is directing a sampling of animal and insect species in areas with varying lovegrass populations at Fort Huachuca.

His findings are incomplete, but he hopes to better understand how plant monocultures can endanger species.

"It's safe to say that these effects are pervasive," Steidl said, but the severity of the threat is unknown.

For someone like Steidl, who is concerned about biological diversity, it's a big deal, he said - though, to the average person driving through a grassland, it could just mean a change in the scenery.

* Contact Tate Williams at 573-4142 or at tjw@azstarnet.com.

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