Utah State University scientists are monitoring plant populations in the valleys south of the Great Salt Lake to learn more about a "dieback" of range shrubs over the past five years.

USU researcher Jim Dobrowolski said the dieback has been especially severe in the Skull, Rush, Puddle and Pine valleys. The dominant plant there is shadscale, which provides winter grazing for sheep and cattle.Dobrowolski and Kern Ewing of the Range Science Department, supported by the federal Environmental Protection Agency, have concentrated their studies in Puddle Valley between the Lakeside and Grassy Mountains.

"Among the possible trigger mechanisms we've been looking at are salt water intrusion from the Great Salt Lake and the waterlogging of soils caused by the above-average precipitation from 1982 to 1985," Dobrowolski said.

"Because many soils in Great Basin Desert valleys don't drain well, standing water may saturate surface soil horizons and deplete oxygen," he said.

The researchers suggest oxygen stress may weaken the shadscale in saturated areas, allowing fungi, bacteria or viruses to invade. The severely cold winter of 1983 and the summer droughts of 1984 and 1985 also may be contributing factors, and the stress on plants may be increased by grazing livestock and plant-eating insects, Dobrowolski said.

Ewing said the Department of Agriculture shrub laboratory in Provo has isolated several fungal pathogens, including water mold, from the dying plants, but the role of the fungi in the dieback is not clear.

Vegetation surveys show that affected strands of shadscale may have five dead shrubs to one live shrub, while in healthy stands, the ratio is reversed.