However, it is very difficult to find terrain other than buildings for any wooden railway. I searched through many different catalogues, and could only find a handful of trees available, and only as part of a much larger set (I think one set was over $100, and included two trees along with a full set of tracks, trains, bridges and whatnot). So I eventually figured out that if I wanted trees, I'd have to build them myself.
So I stopped by Michaels and picked up some cones (wooden doll bodies) and balls (dolls heads) plus a length of dowel and some wooden wheels.
I then got to work cutting the dowel to the necessary length, and glued it in place. The dowel I selected was a perfect fit for the cones and balls, but the holes in the wheels were just a little too big, so I needed to pack them with a bit of modelling putty to get a good fit.
Once the glue dried and the putty set, I slapped on some paint (gloss green for the upper part and a flat brown for the trunk and base).
And here are the trees along with the IKEA train and tracks.
Nice and quick little terrain project. Parts cost me around $25, and I still have lots of paint left over (and I could probably find a cheaper source for parts than Michaels, to boot).