Creating realistic terrain involves more than simply sculpting out a feature and plonking it on the landscape. To truly create a believable landscape, the process of natural grassland formation has to be understood, else grasslands may be placed in locations they have no place being.

Making Grassland

Grassland actually has a lot in common with a hot desert. Both are formed using the same rain-shadow process. Yup, grasslands are driven by the weather. The flow of water on the landscape around the grassland defines its existence. Thus, to create a grassland, the surrounding landscape has to be taken into consideration, as does the weather.

Grasslands are formed by mountain ranges, and by rainfall. The process of making a grassland is actually exactly the same as making a sandy desert, just less extreme.

Water does not sit still. If a world has weather, it has moving water, continually circulating. Water evaporates from any standing body, and flows through the air into greater and greater clouds, rising and rising until it meets colder air, at which point it rapidly condenses and falls as rain. If the clouds rise too high, the water freezes and snow forms. The height of the land forces clouds higher, which is why it snows over mountains.

If the prevailing wind is blowing east, then water collected from bodies of water to the west will evaporate into clouds, and rise over land heading east. Some will fall back as rain, some will survive to reach the mountains, and most will deposit on the western slopes of those mountains. The wind will flow over the mountains, but the last of the moisture will have frozen and fallen as snow or sleet. Ifthe mountains are high enough, it will hardly ever rain on the eastern slopes, or the lands to the east of the mountains. In this case a rain shadow desert will form.

But what if the mountains are lower? In this case, a lot of rain is still lost traversing the mountain, but some remains. Not a lot, but enough for small plants to survive on. The rainfall is not steady, sometimes there is rain, sometimes it can go months without any. This kills off most trees and larger plants. Hardy grasses can survive these conditions, and creeping roots bind the soil together, preventing the wind from blowing it away. A grassland forms.

Fire

Once a grassland has been made, fire helps prevent larger plants growing. A single lightning strike on dry grass can turn a grassland into a blaze. Hot sunlight can start fires in dry grass. These fires sweep across the grassland, destroying everything, except the tough grasses.

After the fire, the grasses return, new growth pushing through the old, burnt bits. Grass never does burn well, and after a fire, with all the competition gone, the grass grows thicker and stronger than ever.

The High Grasslands

Grasslands even form up in the mountains. Above a certain altitude, known as the treeline, the air is cold, dry as all the water is frozen, or near freezing and the air is too rarified to support much humidity. Here, trees and large plants cannot grow, so instead, tere are huge, rolling plains, leading up to the snow line.

The Cool Grasslands

Grasslands in temperate climates have a very cool, cold feel about them. Found usually in the middle of large continents, far from the sea, they whip up strong winds from the lack of tall vegetative cover, and the winters are extremely cold. Most rain falls in late spring to early summer, and towards the end of the summer the grass is brown and fires likely.

From Forest to Desert

A temperate grassland does not have the same climate from one end to another. Formed by lessening amounts of rain on the prevailing wind, it usually borders a forest one one or more sides, where the rain is plentiful, and the soil rich and deep.

Moving downwind, you gradually get a tallgrass prairie, as the rainfall begins to taper off and trees thin out. Continuing downwind, the tallgrass gives way to a midgrass prairie where the soil is good, if not deep, and rainfall is moderate.

Continuing downwind, less and less rain falls. Shortgrass prairies thrive in good or poor soil with low rainfall, where the grass strands hug the ground, and grow more sparsely.

Finally, rainfall peters out, the grasses grow few and far between and the wind begins to wear away the soil. A desert forms at the edge of large grasslands, where the rain simply does not reach at all.