There are only three types of objects that you are able to export from Bryce. They are rocks, lattice and terrains. That is it. To export these objects, simply click on the letter "E" (when the object is selected). Then press CTRL D on the keyboard and the export windows will come up. 3DS will be an option.
The only way to "re-use" an entire scene, is to use the merge feature (under the "file" menu). With this option, you can omly merge one scene or world, with another.
Hope that helps.