     And I'm Melissa Block. Forests in the southwest have become
a fuel stockpile. A century of quashing all fires has allowed
forests to become overgrown. Now, a warming climate is making
the problem worse. Scientists are trying to defuse these green
time bombs, but in today's story, part of our series on wildfire
and climate, NPR's Christopher Joyce reports on whether that's
even possible.  CHRISTOPHER JOYCE, BYLINE: To understand how
wrong things have gone in forests outside Santa Fe, New Mexico,
you have to see them. Along a trail above the city, the limbs of
the Ponderosa pines touch each other. It's not a forest. It's a
green fuzzy blanket with young trees fighting for space and
light, and it makes William Armstrong sick.  WILLIAM ARMSTRONG:
They're a plague. On this forest, it's averaging about 900 trees
per acre. Historically, it was probably about 40. Here in the
national forest, what we're facing is a tree epidemic.  JOYCE:
Armstrong is the U.S. Forest Service's fire manager for the
Santa Fe Nationa