EDWINSTOWE, England — Robin Hood might have a hard time hiding out in the Sherwood Forest of today.

The forest once covered about 100,000 acres, a big chunk of present-day Nottinghamshire County. Today, its core is about 450 acres, with patches spread out through the rest of the county. Experts say urgent action is needed to regenerate the forest and save the rare and endangered ancient oaks at its heart. Some 15 organizations have joined forces to draw up a rescue plan, hoping to win a $100 million grant through a TV competition in December.

“If you ask someone to think of something typically English or British, they think of the Sherwood Forest and Robin Hood,” the regional director of the East Midlands Conservancy Forestry Commission, Austin Brady, said. “They are part of our national identity … but the Sherwood forest is a real place, and the real forest needs help, too.”

The forest is beloved for its connection to Robin Hood, the legendary 13th-century bandit who supposedly hid there from his nemesis, the sheriff of Nottingham, in between stealing from the rich and giving to the poor.

One of Sherwood’s oldest and most celebrated trees is Major Oak near Edwinstowe, the town where legend has Robin marrying Maid Marion. Historians believe it and other Sherwood oaks could have been saplings back in Robin’s time.

Park rangers say the collection of ancient oaks is one of the greatest in Europe. But they see an increase in the trees’ rate of decline. Over the centuries, the forest was carved up for farms, mines, towns, and logging. Sherwood timber built medieval ships and even part of London’s St. Paul’s Cathedral.

Now, the ravages of age — and, some fear, climate change — are taking their toll. On average, one veteran oak a year would fall; this year, seven have come down, and the rate seems to be accelerating, the forest’s chief ranger, Izi Banton, said.

Currently, 997 ancient oaks stand on the 450 acres known as the “beating heart of the forest,” Mr. Banton said. About 450 are still living, and of those, 250 are good shape, while the other 200 are particularly vulnerable. The remainder are standing deadwood, still valuable to the forest because of the life they support.

Each oak has its own management plan, and some even have names, like Medusa, Stumpy, and Twister. Rangers monitor them closely, watching for branches that look droopy or stressed, anxious to ensure that each tree lives as long as possible, a senior ranger, Paul Cook, said.

“Every time I come up here, I think, ‘Has that one gotten slightly lower?'” Mr. Cook said, looking at one aging oak. “It is a shock every time one comes down.”

Ancient oaks survive about 900 years, of which 300 years are spent growing and 300 dying. Of the seven trees already lost this year, four were felled by high winds on one February night.

With fallen trees go the mostly unique kinds of beetles, moths, and bats that live in them.

“It’s the hidden side of Sherwood — everyone knows about the amazing trees, but they’re not aware of life it supports,” Mr. Banton said. “They’re not all cute and fluffy, but they have just as an important role to play.”

The oaks and wildlife will become more vulnerable as long as they remain isolated from the rest of the forest, Mr. Brady said. The rescue plan would focus on planting 250,000 trees to knit the parts of the forest back together.

Hopes are high that Sherwood Forest will win the grant from BIG Lottery, a branch of the National Lottery that gives out money to good causes. Last year, the lottery launched Living Landmarks, a TV program that encourages communities across Britain to work together to improve quality of life and environment.