Chronos, yeah, if you could pick any orbit for the moon that you wanted, you could do that. You could put it at the L1 Lagrange point, like SOHO, too. I was thinking of natural moons, though, and I know of no process that would evolve a moon into that kind of an orbit! The L1 point is unstable, too. Unlike satellites, moons last a long time–and they can’t do station-keeping. : )
nwhittamore, I don’t think that it would be a problem for trees to evolve to cope with long periods of day and night. Remember, these orbits aren’t necessarily 30 days–the orbits of the Galilean satellites are .67, 1.77, 3.55, and 7.15 earth days for Io, Europa, Ganymede, and Callisto, respectively. If the orbital period was very long, the day side would end up pretty warm, and the night side would be a bit nippy, but though I am not a biologist, that doesn’t seem like too insurmountable a problem. During the “night”, the planetward side of the moon would get some shine off the planet, which might help. And the time the moon spends eclipsed behind the planet would be relatively short.
Also, while moons tend to end up in synchronous rotation, it’s not absolutely required. If we take Chronos’ viewpoint and try to set things up just right, we can throw in a few other moons set up just so they keep our forest moon from getting tidally locked. Hyperion, a moon of Saturn, is in just such a situation. Hyperion’s rotation is chaotic, which might not be the healtiest thing for the plantlife, but if you could set things up right, you could probably give the forest moon any rotational period you want.
If you’re interested in reading more about this problem, the Farseer trilogy by Robert Sawyer is set on the inhabited moon of a gas giant. It doesn’t involve much cutting-edge science, but plays on a few interesting consequences of the situation.