Biome



According to Wikipedia, biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems.

In Minecraft, from the Halloween Update onwards, this means different areas with different heights, temperatures, humidity ratings and foliage colors are created.

Before the Halloween update, when a map was generated it got a theme of either Snowy or Grassy. After this update, a single world includes all themes in a logical fashion determined by the biomes graph.

A demonstration can be viewed here.

Pre-Update Saves
Worlds generated before the update were not changed, but the grass color was altered. However, any new chunks generated (by the player moving outside of the pre-biome world's generated bounds) do generate biomes, just as The Nether is generated when you first enter it.

Biome Types


You can tell biomes apart by the differentiating colors of grass and leaves, as well as what kind of blocks are in the area, i.e. cacti in desert, etc. There are 11 Biome types: (Note: these names come from Notch's notes)

Biome Screen-shots
These screenshots were made by editing code in Minecraft's java files, creating worlds made up of only one Biome. This was done consecutively with each Biome type and their screen-shots are collated here. The original topic is on the Minecraft forum is here.

Difficulty
Starting in a biome with almost no trees, like desert or plains, can prove much more difficult than starting in a biome like rain forest because the player won't have as many trees to create a pick or shelter. Even though one can travel to another biome at the very start of the game if the biome is unpleasant, the player would be wasting precious time that could otherwise be spent preparing for nightfall.

Remaining Work
Remaining work on biomes include variable elevations in certain biomes (flat elevation in desert biomes, etc.) in addition to improving the border between arctic and tropical biomes.

Also, snow currently does not "fall", meaning that once snow or ice has melted or been mined, it will not regenerate. Maybe Notch will also add rain in some biomes.