Wipe your train clean. If in doubt, ask those who specialize in the type of trains you have. There is a tendency for all trains to spark when contact wheels hit a gap in the rails. Track is a big part of the problem. Older track does not produce as clean a contact point as newer rails.
Sparks can ignite other things.
Water it daily, so it stays moist and fresh. Once it starts drying, as they all do eventually, it's time to stop running trains near it. Trains or not, tree safety is a must. Keep it from drying during the holidays by frequent watering. The tree skirt should be of a fire-retardant material.