A rendering of the museum from above. the Gilder Center is depicted at the bottom in the middle, near Columbus Avenue.

The main group opposing the expansion of the Museum of Natural History has accepted the near certainty of the project’s approval, and now is focusing on saving as many trees as possible.

The Defenders of Teddy Roosevelt Park announced today that president Sig Gissler is stepping down — he told us “at age 80, six months at the helm are enough.” The group’s board elected Adrian Smith, a landscape architect, to be the new president. The museum plans to construct a new complex called the Richard Gilder Center that will house educational space, exhibition halls, a library and a theater. The Defenders had initially argued that the museum should not encroach on any space in the surrounding Teddy Roosevelt Park. Opponents had begun to flex political muscle, with some loudly decrying City Council member Helen Rosenthal’s financial support for the museum.

But their opposition is mellowing. In a press release issued Wednesday, the Defenders mostly seem pleased that the museum expansion will swallow less parkland than they had feared. Their goal now is to shape the project to be as environmentally conscious as possible.

Some locals remain entirely opposed to the expansion — Cary Goodman, a local resident who also heads a business improvement district in the Bronx that wants the museum to locate there — has led more aggressive protests, including against museum board member Tina Fey. But the Defenders have made it clear that Goodman doesn’t speak for them.

The Defenders’ Wednesday release says:

Formed last July after the American Museum of Natural History proposed a major expansion into Theodore Roosevelt Park at 79^th Street, the Defenders had a significant victory in November when the museum proposed a revised design that would take substantially less parkland than originally indicated.

Now, working with the community, the Defenders is focused primarily on making sure that the redesign of the park fully recreates its highly valued role as the neighborhood’s backyard.

The organization is also concerned about the proposed underground service drive. The museum project would remove two mature canopy trees with trunks that are over two feet in diameter, one of them a majestic English Elm.

“Among the important issues the Defenders intend to work on, tree preservation is high on the list,” Smith said. “The excavation for the underground drive threatens the survival of two important ones, so we’ve encouraged museum officials to change the drive’s layout to avoid the trees’ roots.”

The Defenders is concerned about other questions raised by the museum project, notably traffic congestion and environmental impact. However, the board has concluded that, at this stage, the most productive use of its time and resources is to be an effective voice in preserving the park’s treasured qualities as the redesign process moves forward.