Satellite images of New Orleans taken before (top image) and after Hurricane Katrina hit in 2005. Live trees are represented in green, dead or damaged trees are in red.
Satellite images of New Orleans taken before (top image) and after Hurricane Katrina hit in 2005. Live trees are represented in green, dead or damaged trees are in red. Courtesy USGS
Elizabeth Shogren, NPR
Tulane Professor Jeff Chambers with one of the 320 million trees that he estimates were killed or damaged by Hurricane Katrina.
Tulane Professor Jeff Chambers with one of the 320 million trees that he estimates were killed or damaged by Hurricane Katrina. Elizabeth Shogren, NPR
Elizabeth Shogren, NPR
The mushrooms on this tree are helping it to decompose and release carbon dioxide into the atmosphere.
The mushrooms on this tree are helping it to decompose and release carbon dioxide into the atmosphere. Elizabeth Shogren, NPR
Elizabeth Shogren, NPR
Chambers stands in front of a huge root ball of a tree that was pulled out of the ground when Katrina barreled through the forest.
Chambers stands in front of a huge root ball of a tree that was pulled out of the ground when Katrina barreled through the forest. Elizabeth Shogren, NPR
Elizabeth Shogren, NPR
Margie Jenkins is the matriarch of a family tree farm that was hit hard by Katrina. This field used to be full of mature loblolly pines, but they were devastated by Hurricane Katrina . She has replanted the field with baby trees.
Margie Jenkins is the matriarch of a family tree farm that was hit hard by Katrina. This field used to be full of mature loblolly pines, but they were devastated by Hurricane Katrina . She has replanted the field with baby trees. Elizabeth Shogren, NPR
Almost everyone has heard about Hurricane Katrina's toll on the residents of New Orleans. But Gulf Coast trees also took a wallop. Hundreds of millions of trees were destroyed or badly damaged and have become an unexpectedly large contributor to global warming, according to new research.
In fact, trees killed by Katrina will release about as much global warming pollution into the air as all the trees across the nation soak in over the course of one year, according to a study by Jeff Chambers, a Tulane University biology professor.
Trees are one of the planet's best defenses against global warming because they absorb and store a lot of the carbon dioxide emitted by power plants, factories and cars. But when trees are killed, they decompose and start releasing that carbon dioxide back into the air. Then they become part of the problem instead of the solution to climate change.
And Chambers worries that damage to trees and the climate will increase because global warming is expected to make tree-killing storms like Katrina more frequent.
'There's No Trees'
Chambers evacuated his New Orleans house before Katrina hit. As he was fleeing, he was already thinking about how the research tools he has been using to study the Amazon forest would come in handy to study the hurricane's impact on Gulf Coast forests.
Chambers uses satellite images and on-the-ground surveys to study the damage caused by wind storms in the forests in Brazil. That put him in a perfect position to study the trees killed by Katrina.
He began by hunting down two satellite images: one from two years before Hurricane Katrina and one from a year after the storm. Both photographs were taken in the same month, on clear days.
Much of the area that was live trees before the storm — represented as green in the satellite images — turns red in the image taken after Katrina.
Chambers ran programs to compare the two images, pixel by pixel. Each pixel covers about the size of a basketball court. He picked 25 of them that represent a range of forest damage.
Then he zoomed in on each of those pixels, determined their locations and sent his research team to count and measure the dead trees. He added this field data to the information from the satellite images, did a lot of number crunching and came up with a number of dead trees: 320 million. The amount of carbon dioxide they'll release: about 105 million metric tons.
One of the most damaged pixels is about an hour's drive north of New Orleans at the Pearl River hunting reserve.
Wild hogs are about the only thing in season at Pearl River in late fall, so there aren't a lot of hunters. One of them, Paul Noel, says the area used to be a gorgeous, wide-open forest with mature hardwood trees.
"I'm amazed, I'm absolutely amazed," Noel said. "There's no trees. You can't walk because of the briers."
In the woods, downed trees are everywhere. The trunks of once-massive oaks, sweet gums, pecans and other hardwoods lie in tangles across the forest floor like a massive game of pickup sticks. New growth of trees and sticker bushes are sprouting everywhere.
"This is essentially ground zero for where Katrina made its final landfall," Chambers said.
Carbon Dioxide and Trees
Chambers stops at one downed tree that's covered with mushrooms. The fungus is consuming the dead wood, he explains.
"One of the waste products of carbon dioxide," Chambers said.
Chambers is not the only scientist who has tried to measure Katrina's carbon footprint. Steve McNulty of the Forest Service used field surveys and aerial photography to assess the carbon dioxide that will be released from trees damaged by both Hurricanes Katrina and Rita. He came up with a figure less than half as big as Chamber's estimate.
But McNulty doesn't quarrel with Chambers' findings.
"My estimates are probably somewhat conservative relative to the damage, just because you can't go out and survey all of the damage," McNulty said.
Some in the forestry industry have criticized Chambers' study. They point out that most of Louisiana's forests are privately owned and Chambers didn't do any site surveys on private property. And they stress that Chambers didn't take into consideration the trees that were taken to mills and turned into lumber after the storm.
Jenkins Tree Farm
About an hour drive northwest, loggers are busy cutting down and loading 60-foot-tall loblolly pines at the Jenkins Farm and Nursery.
"The trees that are salvaged during this operation, the carbon will not be released, because it will stay in the form of boards and be used for construction and housing," said Kirk Casanova with the Louisiana Department of Forestry.
The state estimates that about 20 percent of the trees killed by Katrina were harvested. More than 200 acres of them were at the Jenkins' tree farm.
Margie Jenkins, the 86-year-old matriarch of the business, remembers that the storm absolutely devastated the farm.
"You had these trees broke off halfway. A lot of them were leaning, a lot of them laying on the ground," Jenkins said. "It was awful."
Walking through a field of knee-high loblolly pines, Mrs. Jenkins' granddaughter, Amelia Levin, says Chambers missed something else. Some landowners like themselves have replanted, and the saplings are already absorbing carbon dioxide.
"By planting baby trees, that's a hell of a counter measure, I think," Levin said.
Chambers concedes that new trees will soak up carbon dioxide, but he says, there's more to the story.
"The carbon released from all the deadwood will result in a carbon source for many years, and it would take much longer for the gains from photosynthesis and new wood production to make up for those losses," Chambers said.
Besides, Chambers says, it's more important to ponder the big questions. As climate change makes intense storms like Katrina more frequent, will forests be able to absorb and store as much of the world's greenhouse gas pollution as they do now? Probably not, he says. And if they can't, that will make the challenge of keeping climate change in check even tougher.