Trees are randomly-generated structures in the world which can be commonly found outside of a Monarch's kingdom. Most trees can be cut down by builders if they are given one coin, after which an X marking will appear carved in the tree's trunk. After a builder cuts down the tree, it will disappear and the builder will earn 0 to 2 coins that he returns to the Monarch. That area of land is then designated part of the plains biome.
Certain segments of the map such as Ruins, Camps and Background/Foreground Foliage will disappear once enough trees have been cut. Some areas such as Portals and the Hermits Hut will not disappear. If a Monarch is attempting to recruit as many citizens as possible, it is best not to tear down trees next to Camps as this will remove said camps.