You'll notice that the terrain has turned green and this is because the grass and daisies have created a grassland biome. Different species like living in different biomes and you can check their preferences in the "Species Info Panel". Grow a tree in the new grassland biome at a suitable altitude for this task.
- Grow an Oak Tree to over 50% maturity
- Have 1 Oak Tree in the world with an environmental satisfaction of over 70%