Trees, Rocks, and Crystals.
These show up in your village and take up space. They must be removed by the player by breaking them twice before you can place anything.
Hearts and Tools Needed to Break
Trees take one heart each hit and require an Axe.
Rocks take two hearts each hit and require a Hammer.
Crystals take three hearts each hit and require a Pickaxe.
If a player fills every square in their village with some sort of decoration or tree they wont get any obstacles.
The White Lion will limit the number of obsticales you can get in your village to 5.