The most interesting place in a tropical forest remains a virtually unexplored domain. The treetops, where many plants and animals -- including many little-known species -- spend their entire lives, have been out of scientists' reach.

For years, tropical biologists got their only glimpse of the forest canopy when a tree crashed to the ground. And a few athletic scientists managed to ascend into a biological heaven with ropes and pulleys, but the work was cumbersome and dangerous.

Now biologists have devised a way to gain almost unlimited access to the canopy. They have installed a construction crane in the forest.

The technique is being tested by scientists with the Smithsonian Tropical Research Institute, who erected the crane in a forested park near Panama City. A researcher sits in a gondola, which swings out along the length of the crane. The biologist can then lower the gondola into the treetops.

"It's wonderful," said the Smithsonian's Alan Smith.

He said the Smithsonian hopes to install a crane at its biological research station on Barro Colorado Island, a nature preserve in the middle of the Panama Canal. The idea, Smith said, is that in a few years, cranes would dot research sites throughout the tropics and may even be used to explore the canopy of temperate forests in the United States.

"There is more biology in that 80-meter radius than a team of biologists could cover in a lifetime," said Smith. "It gives you unprecendented access."