Based on climate:
* Tropical rainforest: This is the complete opposite in terms of temperature and precipitation.
* Desert: This is the opposite in terms of precipitation, although some deserts can be quite cold.
* Temperate forest: This is the opposite in terms of temperature, but may have similar precipitation levels.
Based on vegetation:
* Forest: This implies a dense growth of trees, the complete opposite of the sparse vegetation of tundra.
* Meadow: This implies a grassy area, which is more typical of warmer climates.
Based on location:
* Equatorial region: Tundra is found in the Arctic, while the equatorial region is the opposite.
* Tropical zone: Similar to the above, this is the opposite of tundra's location.
Ultimately, the best antonym for "tundra" depends on the specific context and what you're trying to contrast it with.