It has set off a heated debate, a federal lawsuit, and enough documents to fill a couple of phone books.

But for the third consecutive year, Valley Forge National Historical Park is proceeding with a deer-culling program designed to thin the herd and encourage new plant growth in the park.

And officials at the famed Revolutionary War site say it is working.

The deer population has long been a bane of Valley Forge, they say. Before the culling began, the park counted 291 deer per square mile. A "sustainable" population would be closer to 35 per square mile, said Deirdre Gibson, the park's chief of resources.

About 1,000 deer were killed during the first two years of the program, reducing the herd to 71 per square mile, she said.

Animal-rights activists have filed unsuccessful court actions to stop the program, which uses federal sharpshooters - mostly military veterans - to kill deer in the park between November and March.

Activists advocated "enhancing" the coyote population in the park to thin the deer herd naturally.

Lee Hall, an attorney for Friends of Animals, which filed suit, argued that deer are dying because humans consider them a nuisance.

"We're expanding the roads, and we find the number of deer inconvenient," she said. "This goes on and on and on. We're not learning to respect and cohabit the environment we are a part of."

Legally, the fight against Valley Forge's culling program ended with an appellate court ruling in favor the park. But Hall and fellow animal activists say they're still committed to speaking out about deer-culling programs in the area, including one approved earlier this year by Radnor Township.

Park officials say they understand residents' concerns about the program.

"We know this is a very painful and emotional decision, and for many people it's just really hard to accept. And I regret that," Gibson said.

Still, she said, the high volume of deer has been destroying the park's ecosystem, eating low-lying plants and forcing out other species.

"Deer were basically occupying the entire environment. There are parts of our forest where there is literally nothing growing on the ground, that are just dirt," Gibson said. "This evens the playing field."

The East Coast, Pennsylvania in particular, has long dealt with burgeoning deer populations as the area's human population has become more urbanized. Increased development has pushed many of the deer's natural predators out of the suburbs, and deer have adapted well to suburban environments, where they thrive with no predators to keep their population in check.

"No one anticipated this, but the problem has increased, increased, increased," Gibson said.

Some who live near the park say they're pleased with the program. Bruce Davis, who lives on the edge of the park in Wayne, said it wasn't unusual for him to arrive home each night to find six to 10 deer on his lawn.

"Many of my neighbors have contracted Lyme disease, and many of my neighbors have had damage to our automobiles due to the deer," he said. "They would destroy all plants in your yard - we had to replace literally all my landscaping with deer-resistant plants, and sometimes even that didn't work."

Davis said he'd seen far fewer deer in the neighborhood since the cullings began. During the first culling, officials reported, sharpshooters killed 600 deer - nearly half the park's population - and donated nine tons of deer meat to food banks.

"Most importantly, I haven't had to swerve or slam on my brakes when coming into my neighborhood because they're not darting across streets," Davis said.

Gibson said that Valley Forge would conduct a thorough survey of the program's effect on the park next year, but that she'd heard promising anecdotal evidence of plant regeneration.

"It's exciting to see those little green shoots come up and not just get eaten right away," she said.

Contact Aubrey Whelan at 610-313-8112, awhelan@philly.com, or follow @aubreyjwhelan on Twitter.