aspen

[AHill]

The best use of aspen is to leave it growing and go look at the glorious bright golden yellow foliage in autumn. As the others have mentioned it's very soft.

[MichaelMouse]

Neither can you buy aspen timber in Finland from the ordinary timber merchants but as this is a country of small landowners aspen timber is always available if you bother to fetch it from the woods. If there is a sawyer locally anything can be made.
Every woodworker should really have a few hectares of woodland and an old tractor. It removes lots and lots of limitations opening up a world of possibilities.

Aspen is available as "whitewood" or "popple" or even aspen lumber.  What it's not called is "poplar", which it is, because the name is used by lumber which isn't, just as "cedar" is used in many varieties....