The culling - deer are lured to specific areas and then shot - will end when the deer-density or forest-regeneration goals are reached. Then the park will use reproductive control - assuming a safe agent becomes available - to maintain a desirable deer population.
Deirdre Gibson, chief of resources for Valley Forge, said the program had already yielded positive results.
The park has had a large increase - more than 800 percent - in tree seedlings since the culling began, and the surviving deer have become healthier, heavier, and more fertile. More than 20 tons of meat have been donated to local food banks.
One day, contraception will be an option, Gibson said. Health risks could result if deer were treated with immunocontraceptives and then shot and consumed by humans, Lawhon said.
Valley Forge officials said their management methods are safe and humane. Marksmen are familiar with the park geography and are trained to conduct shootings in suburban areas. The culling takes place at night after the park closes.
"Keep people with guns out. That's what parks should be doing," said Priscilla Feral, president of Friends of Animals, an advocacy group based in Darien, Conn. She called Valley Forge's plan "deplorable" and "an affront to decency."
Activists from Friends of Animals and Compassion for Animals, Respect for the Environment (CARE) filed an unsuccessful lawsuit against Valley Forge, opposing the deer-reduction plan. The lawsuit argued that the Pennsylvania Game Commission could instead stop hunting and trapping coyotes, allowing their population to rebound and naturally keep deer levels in check.
Lee Hall, an environmental lawyer who helped develop the case for the two nonprofits, said deer should not be the park's biggest concern.
Cars zoom through Valley Forge, using it as a cut-through, she said. Horses trample the hills, and the park is so crowded by human tourists parking is often difficult to find.
Deer were once an endangered species in Pennsylvania. They had to be imported in the early 20th century. But the population increased as humans built suburbs and development pushed out many natural predators.
Then, depleted again by unrestricted hunting, strict game-management measures were needed to restore the population.
For humans, sharing backyards and roads with deer can be difficult. The ravenous herbivores are known to feast on plants and flower beds, and they dart out onto roads.
Last year in Pennsylvania, State Farm Insurance estimated deer-vehicle collisions resulted in more than $400 million in damage.
As Valley Forge looks to enter its fifth year of deer-culling next winter, Houdret said he hopes the park will use an outside, independent group to count the population before it continues with the management plan.
"I can't imagine where they're going to find a deer to shoot," he said.
BY THE NUMBERS
Deer killed in 2010-11 Valley Forge hunt.
Deer killed in 2011-12.
Deer killed in 2012-13.
Deer killed in 2013-14.
SOURCE: National Park Service