"On any given day, there's a wildfire burning somewhere in the U.S. — and that's not necessarily a bad thing. Many western forests have evolved with fire, and actually benefit from the occasional wildfire."

"A nice little ground fire every few decades cleans house in the forest. It burns the grass and brush, and maybe some smaller trees — the 'ladder fuels' that might carry a fire up into the tree canopy. Those canopy fires are the worst kind — they kill forests.

But scientists are discovering that some trees in the West that previously would survive and thrive with small fires are now losing their ability to do so.

Philip van Mantgem, a research ecologist with the U.S. Geological Survey, has found a pattern to explain why."

Christopher Joyce reports for NPR's All Things Considered July 29, 2013. [2]