Central Park this summer may seem a bucolic oasis, and it is widely considered one of the nation’s most successful urban parks. Yet beneath the surface, experts say, it is suffering the debilitating effects of time and modern use, and it will decay further unless its historic structures and landscapes are restored. On Thursday, the Central Park Conservancy is set to announce an ambitious 10-year, $300 million fund-raising and improvement effort.

The conservancy’s plan, “Forever Green: Ensuring the Future of Central Park,” might sound excessive, an effort by rich New Yorkers to spruce up their backyard when other neighborhoods are in dire need of better open spaces. Only four years ago the conservancy received $100 million from the hedge fund manager John A. Paulson. But others argue that the park has been a victim of its own success. As it has been improved over the years, the number of annual visitors has mushroomed to 42 million, from 12 million in 1981.

“It’s being trampled to death — visitation now is heavier than ever in its history,” said Adrian Benepe, the former New York City parks commissioner who is now the director of city park development at the nonprofit Trust for Public Land. “This is America’s great work of art of the 19th century because it set a standard for what a great urban park should be that has been copied all around the world.”