A state and federal report on the 1,000-square-mile Murphy Complex fire in southern Idaho and northern Nevada concluded that weather and dense grass were more important factors than livestock grazing in the 2007 blaze.

Environmentalists last year said climate change, drought and the Bureau of Land Management’s planting of grasses favored by cattle - but more flammable than native plants - exacerbated the fires.

However, this week’s 49-page report concluded that spring rains spurred dense grass growth; then, strong winds, near 100-degree temperatures and a violent lightning storm on July 16 2007 fueled the largest fire ever fought by the BLM in Idaho.

The fire, which burned for three weeks, cost more than $13 million to fight and a record $23 million to rehabilitate a portion of the burned lands and promote their natural recovery.

The report was released by the universities of Idaho and Nevada, the U.S. Department of Agriculture, the U.S. Geological Survey, the BLM and the Idaho Department of Lands. (AP)