Sierra fires have become larger and more damaging in the last 20 years Forest fires in the Sierra Nevada have grown larger, more frequent and more damaging in the last two decades, according to a study that suggests much of the blame rests with the government's century-long war on wildfire. The study, published online this month in the journal Ecosystems, found that between 1984 and 2006, the proportion of burned areas where no trees survived increased, on average, to nearly 30%, from 17%. Climate is playing some role, the study said. But it blamed a bigger factor: Federal efforts to quench most blazes quickly have thwarted the Sierra Nevada's natural cycle of frequent, house-cleaning fires and left forests packed with fuel. "This just blind effort to continue to put everything out is probably backfiring on us," said Hugh Safford, a U.S. Forest Service ecologist and one of the study's authors. "We've created our own nightmare." Blazes in mid- and low-elevation forests have grown more severe in large part because there is more to burn. A jump in average annual precipitation across the range since 1908 has promoted forest growth, while a rise in temperature is diminishing the mountain snowpack and lengthening the fire season....