In one satellite photograph, bright green pixels mark much of the ground in eastern New Orleans, sprawled south of Lake Pontchartrain and far east of the Industrial Canal.

In another photo, large swaths of that same land show up as deep red, marking devastated former forest areas that include much of Bayou Sauvage National Wildlife Refuge, a 23,000-acre region of former greenery.

The side-by-side comparison in photos taken by the U.S. Geological Survey about a decade ago shows some of the estimated 100,000 trees killed in the New Orleans area after Hurricane Katrina barreled through the city 11 years ago Monday.

It’s a tiny portion of the impact the storm had on foliage in the Gulf Coast overall. An estimated 320 million trees are thought to have been damaged or killed in Mississippi and Louisiana after Katrina — an unprecedented loss that local researchers in 2007 estimated would change the area’s ecosystem for the worse for generations to come.

Fast-forward to 2016, however, and officials with New Orleans’ numerous organizations dedicated to protecting green spaces are celebrating what they call an unanticipated comeback for the city’s trees.

After more than a decade of concerted efforts by city organizations and nonprofit groups, the latest tallies show about half of the trees lost to Katrina have been replanted in public spaces alone — a number that doesn’t include private homeowners or other individuals who have taken it upon themselves to restore some of the city’s green canopy that had been decimated after the storm.

“If it’s one good thing that the storm did bring, it certainly did bring a level of community engagement to bring back and preserve the city’s public green space,” said Ann Macdonald, director of the city’s Department of Parks and Parkways. “It made people much more passionate about our city and made them want to preserve our native plants.”

As of late August, Macdonald said, 50,000 trees have been replaced post-storm in public spaces in New Orleans, thanks to more than a decade of partnerships and federal grant money.

Among the organizations the city has worked with closely are Parkway Partners, a nonprofit founded by residents in 1982 in response to city cuts in the Parks Department budget, and the nonprofit NOLA Tree Project, formerly called Hike for KaTREEna.

A grand total is difficult to calculate, but Macdonald said she knows the number of newly planted trees is even higher, because those organizations frequently give away free trees, which then are planted in residents’ yards.

“Our goal is to replace the trees as much as we possibly can,” Macdonald said. “I can see, as I ride through the city and the major corridors, that the young trees are coming in and now growing, and that we’ve had a real impact.”

Some areas are unrecognizable from the months after the storm, when large pockets of trees were uprooted and died after sitting for months in brackish floodwaters. To this day, Macdonald remembers the “major corridors” of trees lost in areas like Paris Avenue in Gentilly, where every single magnolia succumbed to the flood after the trees' root systems were damaged.

By mid-2006, the Federal Emergency Management Agency and the Army Corps of Engineers alone had collected 20 million cubic yards of tree debris, according to reports published then by The Times-Picayune, and the cleanup process was still underway.

Overall, it was estimated that 70 percent of the city’s canopy was lost. In 2012, a U.S. Forest Service study found that New Orleans had suffered the greatest decline in urban forest of any city since 2005.

That, experts say, didn’t only affect the beauty of the city’s landscape but also removed trees that provided protection from flooding, decreased air pollution, lowered utility bills because of the shade they provided and welcomed insect-eating songbirds.

Brackish water wasn’t the only tree-killing culprit after the storm, when cypress, oaks, pines and ash all died. According to the Louisiana Department of Agriculture and Forestry, wind damage from Hurricanes Katrina, Rita and Gustav damaged the trunks of trees and the inner bark of those that were already unhealthy and exposed.

Many of the trees stressed by those storms were then made more susceptible to insects such as bark beetles, the department wrote in a report analyzing the state’s forest conditions in 2014. Other trees died from sheer physical damage, or from various fungi that entered cracks, abrasions and breakage.

Buck Vandersteen, the executive director of the Louisiana Forestry Association, estimates that more than 4 billion board feet of trees were laid on the ground during Katrina and Rita — or the amount needed to make hundreds of thousands of homes.

“Basically, three times our normal annual harvest was placed on the ground in a matter of six hours for each storm,” Vandersteen said. “That was a tremendous impact on the industry and the land owners that grew them.”

Over time, that loss has been mitigated, Vandersteen said, as his organization plants about a hundred million trees every year in Louisiana forests.

Things in New Orleans are returning back to normal, too, local experts say. Neutral grounds that were once barren are again sporting plants that many say are integral to the fabric of the city’s character.

Kristi Trail, the interim director of Parkway Partners, recalls the first planting her organization did after Katrina, in December 2005 in Lee Circle — a moment she called a “big symbol” for the city.

The year after that, volunteers planted 200 live oak trees on Elysian Fields Avenue. Since then, the number of trees Parkway Partners has put in the ground has ballooned to more than 13,000.

The organization is still in the process of replacing trees, and it has just signed an agreement with a neighborhood organization in Broadmoor to plant more, Trail said. Through a program called Tree Troopers, Parkway Partners offers a free class to teach residents how to take care of the newly planted trees.

The NOLA Tree Project, too, has in recent years announced a new focus on sustainability. That shift happened when Connie Uddo took over as executive director and changed the name from Hike for KaTREEna.

Rather than recruiting volunteers to plant trees for the organization, Uddo now shepherds a program called the Big Treezy giveaway, which donates trees to residents and schools for free.

Just last year, the organization partnered with five charter schools to teach them how to plant fruit orchards — and, importantly, how to maintain them.

Ultimately, the group aims to plant 100,000 trees, one for each tree lost because of Katrina. So far, they’ve put 34,000 in the ground, Uddo said. She’s also focusing on mulching, tree trimming and teaching people how stormwater management plays a role in the sustainability of the city’s urban tree canopy.

“We pulled back on a lot of tree planting in the last few years, mostly because we weren’t being good stewards of the trees in the ground,” Uddo said. “We want these trees to be here for 80, 100 years.”

Like Uddo, Trail cautions that there’s still much work to be done — particularly in large areas of New Orleans East, where she says not enough has changed from that decade-old satellite photo taken near Bayou Sauvage.

“When you head farther east, there is a huge gap between the number of trees that should be there and the number that are actually there,” Trail said. “We’d still like to see more focus out there on getting more trees.”

Follow Della Hasselle on Twitter, @dellahasselle.