Minecraft wiki entry for Biome, associated text: The content of any particular biome is pseudo-randomly generated from the map seed under control of rules specific to its biome type. These rules govern the distinguishing features of the biome, such as the large-scale shape of its surface; the types of structural blocks it's built of (particularly its ground cover blocks such as podzol or sand); the color shading of its grass, foliage, and water; and the kinds of plants and species of trees that grow in it.