So, I have created characteristic soundscapes for each place. A soft wind and farmland birds for the grassland, wind in the trees, turtledove and woodland birds for the temperate forest, and so on.
Each biome has a weight so that, when you go from one area to the next, a soft transition takes place. Notice in the video below how we softly travel from the temperate forest to the taiga (around 0:16). The woodland birds fade out progressively to let the taiga birds and a fresh wind fade in.