DAVID GREENE, HOST:
A couple weeks ago, I was touring the burned-out town of Paradise, Calif., with residents James and Lisa Gaebe, when this happened...
(SOUNDBITE OF TREE CRASHING TO GROUND)
GREENE: What was that?
LISA GAEBE: ...Houses looked like.
JAMES GAEBE: A tree.
L. GAEBE: Probably a tree, yeah.
J. GAEBE: Sounds like a tree went down. That looks like the route we just came from.
L. GAEBE: It's definitely not safe.
GREENE: That was a huge tree, weakened by the fire, crashing down without any warning. And this is one of the many dangers as residents try to return to a place devastated by a wildfire. Montana Public Radio's Eric Whitney reports.
ERIC WHITNEY, BYLINE: Falling trees are one of the big reasons it can take so long for people to be let back into areas evacuated for fires. Scott McLean, a spokesman for the California Department of Forestry and Fire Protection - or Cal Fire - says, checking for them is very time- and labor-intensive.
SCOTT MCLEAN: The firefighters are going throughout every street, walking it, making sure that trees, poles, whatever it may be, are secure. If they're not, we'll cut them down.
WHITNEY: McLean says people will be let back in when authorities determine there's less danger. But Cal Fire still advises...
MCLEAN: Keep your eyes, your ears open. Look up, look down and look around. There is no sure situation. They need to make sure that they are safe as well and to provide for their own safety.
WHITNEY: Hazard trees can be hard to identify. McLean says some firefighters will knock on them, kind of like supermarket shoppers do to watermelons. If a tree sounds hollow, it could be bad news. Fire science Professor Scott Stephens at UC Berkeley says different kinds of trees pose different challenges. The pine and fir trees around Paradise often have high branches that fall off without warning. And then there are the oak trees.
SCOTT STEPHENS: I would be very nervous about big oaks and potential for them to come down because the oaks, a lot of times, have heart rot. They have rotten material inside the center. And a lot of times a smoldering fire can burn in there for days and days and days. I've been around oaks like that. And all of a sudden, a week later - boom - it comes down.
WHITNEY: The danger can persist a lot longer than a week, Stephens says, as burned trees that are strong now continue to deteriorate.
STEPHENS: Probably by year four, five, they start to really get less structurally sound. Then, of course, you get a wind event, big storms, and they start coming down in earnest. And by year 10, they're coming down a great deal.
WHITNEY: Public safety agencies, like Cal Fire, generally cut down hazard trees immediately after a fire. Then it's up to individual property owners to take care of trees that may be problematic longer-term. Stephens says fire insurance policies often cover the expense of hiring professional crews to do the dangerous work.
STEPHENS: I would not advocate for anybody to do this work on their own. It's quite a skill, quite an artform, frankly, to get a big tree to drop where you want it.
WHITNEY: Stephens says he's worried about how many people in and around Paradise have fire insurance. He says sometimes counties or other jurisdictions will pool resources to contract with professional tree fallers to work at community scale. Timber mills can process a lot of fire-killed trees into useful lumber, but timber companies are generally only interested in burned areas outside of town, where they can salvage logs efficiently. Stephens says logistics make it unlikely that small property owners will be able to sell dead trees to offset the cost of cutting them down.
STEPHENS: Getting machines in there to collect these materials, having all the burned debris, cars, road infrastructure down - power lines. So it's very difficult for someone to come in and really use that as a viable alternative.
WHITNEY: Like the Camp Fire itself, trees killed by the fire are at first dangerous and unpredictable, and then become an expensive headache for years to come. For NPR News, I'm Eric Whitney. Transcript provided by NPR, Copyright NPR.